Abstract

Taurine is considered a conditionally essential amino acid for fish, so its supplementation may improve feed conversion. This study evaluated the supplementation of taurine on growth performance, hematological and immunological parameters, production costs, and survival of Nile tilapia (Oreochromis niloticus) juveniles raised in a recirculating aquaculture system (RAS). A control diet was formulated with 360 g kg^-1 of crude protein without fish meal and without taurine supplementation (Control). From the control diet, another diet supplemented with 9.7 g of taurine per kg of feed (Taurine) was produced. Fish fed diet supplemented with taurine had lower daily average weight gain and final average weight compared to the control diet (p < 0.05). It was observed that taurine had no influence on condition factor, survival, or hemato-immunological parameters of Nile tilapia juveniles, but there was a higher mean corpuscular volume and greater nitrogen retention in fish from the control group (p < 0.05). It is concluded that Nile tilapia juveniles do not benefit from taurine supplementation in RAS, even when fed diet containing plant-based protein sources.

Key words
amino acid; hematology; nutrition; Oreochromis niloticus; sustainability

INTRODUCTION

The rise of aquaculture production and instability in the supply of fishmeal, market has been seeking alternative sources to reduce dependence on this ingredient, which is the main animal protein source used in commercial tilapia diets (FAO 2022FAO. 2022. The state of world fisheries and aquaculture. Opportunities and challenges. Food and Agriculture Organization of the United Nations.). Plant-based protein sources, especially oilseed plants such as soybean meal are one of the most used sources to replace marine protein, due to their acceptable protein level, adequate amino acid content, economic opportunities, consistent quality, and because they are considered a source of renewable ingredient (De Souza & De Oliveira 2018DE SOUZA IS & DE OLIVEIRA PHC. 2018. Utilização da biomassa de Artemia franciscana como aditivo alimentar no cultivo laboratorial do camarão marinho Litopenaeus schmitti. Holos 3: 98-111., Martinelli 2016MARTINELLI SG. 2016. Suplementação de taurina em dietas para Jundiá (Rhamdia quelen). Tese de Doutorado, Universidade Federal de Santa Maria, 1-94 p., Naylor et al. 1998NAYLOR RL, GOLDBURG RJ, MOONEY H, BEVERIDGE M, CLAY J, FOLKE C, KAUTSKY N, LUBCHENCO J, PRIMAVERA J & WILLIAMS, M. 1998. Nature’s subsidies to shrimp and salmon farming. Science 282: 883-884., Tacon et al. 2011TACON, AGJ, HASAN MR & METIAN M. 2011. Demand and supply of feed ingredients for farmed fish and crustaceans: trends and prospects. FAO Fisheries and Aquaculture Technical Paper, 564, 1-102 p.).

Despite plant-derived protein sources showing some satisfactory results, especially with omnivorous species, they are limited in several amino acids, including taurine and its precursors, which may be necessary for optimal performance and metabolism in aquatic animals (De Souza & De Oliveira 2018DE SOUZA IS & DE OLIVEIRA PHC. 2018. Utilização da biomassa de Artemia franciscana como aditivo alimentar no cultivo laboratorial do camarão marinho Litopenaeus schmitti. Holos 3: 98-111., El-Sayed 2006EL-SAYED A-FM. 2006. Tilapia culture. CABI, Wallingford. El-Shafai SA, El-Gohary FA, Nasr FA, van der Steen NP, Gijzen HJ, 42-43 p., Kuzmina et al. 2010KUZMINA VV, GAVROVSKAYA LK & RYZHOVA OV. 2010. Taurine. Effect on exotrophia and metabolism in mammals and fish. Zh Evol Biokhim Fiziol 46(1): 19-27., Martinelli 2016MARTINELLI SG. 2016. Suplementação de taurina em dietas para Jundiá (Rhamdia quelen). Tese de Doutorado, Universidade Federal de Santa Maria, 1-94 p., Tacon et al. 2011TACON, AGJ, HASAN MR & METIAN M. 2011. Demand and supply of feed ingredients for farmed fish and crustaceans: trends and prospects. FAO Fisheries and Aquaculture Technical Paper, 564, 1-102 p.).

Among the numerous physiological functions in which it is involved, taurine is a very important compound in lipid metabolism, as it acts as the only amino acid conjugated to bile salts in teleost fish, forming acids (taurocholic and taurochenodeoxycholic) that act in the solubilization or emulsification of fats, making its more accessible for digestion (Chatzifotis et al. 2008CHATZIFOTIS S, POLEMITOU I, DIVANACH P & ANTONOPOULOU E. 2008. Effect of dietary taurine supplementation on growth performance and bile salt activated lipase activity of common dentex, Dentex dentex, fed a fish meal/soy protein concentrate-based diet. Aquaculture 275(1-4): 201-208., Huxtable 1992HUXTABLE RJ. 1992. Physiological actions of taurine. Physiol Rev 72(1): 101-163.).

Taurine is characterized as a non-essential amino acid for some species of fish, such as Nile tilapia (Gonçalves et al. 2011GONÇALVES GS, RIBEIRO MJP, VIDOTTI RM & SUSSEL FR. 2011. Taurine supplementation in diets for Nile tilápia Oreochromis niloticus. World Aquaculture, 6-10 p.), its effects on fish physiology, metabolism, and nutrition have been increasingly investigated in different species of freshwater and marine fish. Recent studies have shown that the presence of taurine in the diet is essential for the proper development of aquatic species, however, its synthesis differs widely depending on the species, size, feeding habits, and activity of the enzyme cysteine sulfonate decarboxylase (Al-Feky et al. 2016AL-FEKY SSA, EL-SAYED AFM & EZZAT AA. 2016. Dietary taurine enhances growth and feed utilization in larval Nile tilapia (Oreochromis niloticus) fed soybean meal-based diets. Aquacult Nutr 22(2): 457-464., El-Sayed 2014EL-SAYED A-FM. 2014. Is dietary taurine supplementation beneficial for farmed fish and shrimp? A comprehensive review. Rev Aquac 6(4): 241-255.).

In studies with Nile tilapia larvae, supplementation with taurine resulted in better growth levels and feed efficiency, suggesting 9.7 g kg^-1 of dietary taurine (Al-Feky et al. 2016AL-FEKY SSA, EL-SAYED AFM & EZZAT AA. 2016. Dietary taurine enhances growth and feed utilization in larval Nile tilapia (Oreochromis niloticus) fed soybean meal-based diets. Aquacult Nutr 22(2): 457-464.). Other studies have shown taurine as a feeding stimulant for species such as European seabass (Dicentrarchus labrax) and giant tiger prawn (Penaeus monodon), making its supplementation in diets recommendable whenever maximum performance in aquaculture is sought (Carr 1982CARR WES. 1982. Chemical stimulation of feeding behaviour. In: Chemoreception in Fishes (Hara, T.J. ed.). Elsevier, Amsterdam, p. 259-273., Coman et al. 1996COMAN GJ, SARAC HZ, FIELDER D & THORNE M. 1996. Evaluation of crystalline amino acids, betaine and AMP as food attractants of the giant tiger prawn (Penaeus monodon). Comp Biochem Physiol A Physiol 113A: 247-253., Martinez et al. 2004MARTINEZ JB, CHATZIFOTIS S & DIVANACH P. 2004. Effect of dietary taurine supplementation on growth performance and feed selection of sea bass Dicentrarchus labrax fry fed with demand-feeders. Fish Sci 70: 74-79.).

Therefore, the aim of this study was to evaluate the growth performance, hematological and immunological parameters, and survival after experimental infection against Aeromonas hydrophila in Nile tilapia juveniles (Oreochromis niloticus) fed with a taurine-supplemented diet.

MATERIALS AND METHODS

The experiment was carried out at Laboratório de Aquicultura of Instituto Federal Catarinense – Campus Araquari, and all procedures carried out in this study were approved by the Ethics Committee on the Use of Animals under protocol number 263/2018.

Experimental diets

The diets used in this study were produced by NUTRICOL® in São Ludgero, Santa Catarina, Brazil. The dry ingredients, including corn, soybeans, and wheat bran, were ground to a particle size of less than 0.42 mm before being mixed with the other macro and micro ingredients. The mixture was then homogenized in a horizontal paddle mixer for 4 minutes and ground again to a size of 800 µm. It was then extruded at 105 °C using an extruder (FERRAZ®, Ribeirão Preto, SP, Brazil) with a capacity of 3000 kg h^-1, producing 3 mm diameter extrudates, according to the methodology used by Stockhausen et al. (2022)STOCKHAUSEN L, VILVERT MP, SILVA MD, DARTORA A, KRAINZ R, FERREIRA GB, DA SILVA LR & JATOBÁ A. 2022. Practical diet with total replacement of fishmeal by soybean meal for Nile tilapia: growth performance and health effects. Cienc Anim Bras 23: 71567..

The present experiment involved two treatments (Table I): a control diet, formulated with practical ingredients and devoid of fish meal (Stockhausen et al. 2022STOCKHAUSEN L, VILVERT MP, SILVA MD, DARTORA A, KRAINZ R, FERREIRA GB, DA SILVA LR & JATOBÁ A. 2022. Practical diet with total replacement of fishmeal by soybean meal for Nile tilapia: growth performance and health effects. Cienc Anim Bras 23: 71567.), and a taurine-supplemented diet, which contained the same practical ingredients and was supplemented with taurine at a level of 9.7 g kg^-1 of feed (Al-Feky et al. 2016AL-FEKY SSA, EL-SAYED AFM & EZZAT AA. 2016. Dietary taurine enhances growth and feed utilization in larval Nile tilapia (Oreochromis niloticus) fed soybean meal-based diets. Aquacult Nutr 22(2): 457-464.). Both diets were isoproteic and isoenergetic and formulated to meet the nutritional requirements of tilapia, as outlined by the NRC (2011)NRC - NATIONAL RESEARCH COUNCIL. 2011. Nutrient Requirements of Fish and Shrimp. Washington, DC: National Academy Press, 392 p. https://doi.org/10.17226/13039.
https://doi.org/10.17226/13039... . Samples of the diets were analyzed for their aminogram using high-performance liquid chromatography (HPLC) and proximate composition using the AOAC (2005)AOAC - ASSOCIATION OF OFFICIAL ANALYTICAL CHEMISTS. 2005. Official Methods of the AOAC International, 18th ed., Maryland, USA. methodology (Table II) at CBO ANÁLISES LABORATORIAIS.

Experimental design

The study used of 200 Nile tilapia juvenile (O. Niloticus) with an average weight of 13.3 g. The fishes were placed in eight polyethylene tanks (800 L) with 25 fishes per tank. The tanks were equipped with a water recirculation system, which renewed 150% of the water per day with a biological filter. The experimental units were randomly divided into two groups, with four replicates each. The first group served as a control and was fed a commercial diet made with practical ingredients. The second group was fed the same practical diet supplemented with taurine. The experiment lasted for eight weeks.

Physicochemical parameters of water quality and food management

The animals were fed three times per a day (9:00 am; 11:00 am and 3:30 pm), with 3 to 6% of their total biomass. Whenever necessary, the experimental units were cleaned to remove excess organic matter. Throughout the experiment, the water’s dissolved oxygen and temperature were checked twice a day, and toxic levels of ammonia, pH, nitrite, nitrate, and alkalinity were measured weekly using an Alfakit photocolorimeter.

The water quality parameters were monitored continuously during the experiment, and the following parameters were recorded: dissolved oxygen levels 3.88 ± 0.81 mg L^-1 and a temperature of 26.54 ± 1.56 °C (measured using YSI PRO20 Oximeter); ammonia levels 0.08 ± 0.08 NH₃ mg L^-1; nitrite levels 1.76 ± 2.68 mg L^-1; nitrate levels 1.71 ± 2.35 mg L^-1; alkalinity levels 97.84 ± 14.31 mg CaC0₂ L^-1; and a pH of 6.88 ± 0.08.

Hematological and immunological analyzes

For the hematological analyses, five fish per tank (20 per treatment) were anesthetized with Eugenol (50 mg L^-1) and aliquots of blood were taken from the caudal vessel, with EDTA anticoagulant, for the performance of blood extensions in duplicate, and determination of hematocrit (Goldenfarb et al. 1971GOLDENFARB PB, BOWYER FP, HALL E & BROSIUS E. 1971. Reproducibility in the hematology laboratory: the microhematocrit determination. Am J Clin Pathol 56: 3539.), plasma glucose (Free® G-TECH), total erythrocyte count, hemoglobin concentration, and calculation of hematimetric indices including mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and mean corpuscular hemoglobin concentration (MCHC). Extensions were stained with Giemsa/MayGrünwald stain (Rosenfeld 1947ROSENFELD G. 1947. Corante pancrômico para hematologia e citologia clínica: Nova combinação dos componentes May-Grunwald e do Giemsa num só corante de emprego rápido. Mem Inst Butantan 20: 29-334.) for total and differential WBC count.

For immunological analysis, 0.5 mL of blood from five animals per experimental unit was collected by puncturing the caudal vessel, without anticoagulant to obtain blood serum. After coagulation, the blood was centrifuged at 1400 g for 10 min to separate the serum, which was collected and stored at -20 °C for subsequent immunological analysis. The concentration of total serum protein was measured with the Total Protein Kit (Biochemical Reagent, Total Proteins, LabTest, Brazil), using bovine albumin to prepare the standard curve. Total immunoglobulin concentration was measured according to the method described by Amar et al. (2000)AMAR EC, KIRON V, SATOH S, OKAMOTO N & WATANABE T. 2000. Effects of dietary βcarotene on the immune response of rainbow trout Oncorhynchus mykiss. Fisheries Science 66(6): 1068-1075., where 100 μL of blood serum was mixed with 100 μL of 12% polyethylene glycol (PEG) solution (Sigma-Aldrich), for subsequent incubation at room temperature for two hours, in order to precipitate the immunoglobulin molecules. The precipitate was removed by centrifugation at 5000g at 6°C for 10 min. After removing the supernatant, the amount of total protein was measured using the Total Protein kit (Lab Test®). The total immunoglobulin concentration is expressed in mg mL^-1, calculated by the formula:

Total immunoglobulin = (total protein treated with PEG - total plasma protein) / volume (mL)

Body indices and condition factor (k)

To determine the hepatosomatic (IHS) and viscerosomatic (IVS) indices, three fish were taken from the hematological collection sample and their liver + bile, viscera, and eviscerated parts were removed and weighed. The weight/length ratio and the allometric condition factor were calculated using Santos (1978)SANTOS EPD. 1978. Dinâmica de populações aplicada à pesca e piscicultura. Hucitec / Edusp, São Paulo, SP, 1-129 p. formulas, as follows:

HSI: hepatosomatic index (%);

LW: liver weight;

CW: carcass weight.

VSI: vicerosomatic index (%);

GW: guts weight;

CW: carcass weight.

Nitrogen and potassium retention

Twelve fish samples (four before the rearing period, four after the rearing period from the control treatment and four from fish fed with taurine) were euthanized, frozen and lyophilized to be sent to CBO ANÁLISES LABORATORIAIS to evaluate the concentration of nitrogen and potassium according to AOAC (2005)AOAC - ASSOCIATION OF OFFICIAL ANALYTICAL CHEMISTS. 2005. Official Methods of the AOAC International, 18th ed., Maryland, USA. methodology.

Experimental challenge

A bacterial inoculum isolated from a strain was plated on PCA plates (plate count agar). After growth at 30 °C for 24 h, a bacterial colony was inoculated into BHI broth and the suspension was incubated at 30 °C for 24 h. After incubation, the culture was serially diluted (1:10) to 1x10⁸ colony forming units (CFU) mL^-1 and seeded in PCA to determine the bacterial concentration of the initial inoculum. To construct a growth curve, bacterial inoculum was serially diluted (1:2) in triplicate in 96-well microtiter plates for 12 times, and the absorbance of each well was measured at 630 nm using a microplate reader. For the infection experiment, a pure bacterial culture grown in BHI broth at 30 °C for 24 h, in static incubation, was centrifuged for 30 min at 1800 g. The supernatant was discarded, and the pellet was resuspended in a sterile 0.65% saline solution to maintain the bacteria concentration at 2.1x10⁸ CFU mL^-1. The bacterial suspension was diluted to the desired concentration for the experiment.

For the experimental challenge, five fish per experimental unit (20 per treatment) were inoculated intraperitoneally with 100 µL of Aeromonas hydrophila (ATCC 7966) at a concentration of 2.5 × 10⁶ CFU mL^-1 (Stockhausen et al. 2022STOCKHAUSEN L, VILVERT MP, SILVA MD, DARTORA A, KRAINZ R, FERREIRA GB, DA SILVA LR & JATOBÁ A. 2022. Practical diet with total replacement of fishmeal by soybean meal for Nile tilapia: growth performance and health effects. Cienc Anim Bras 23: 71567.). After 96 hours, fish survival was evaluated.

Growth performance

At the end of the experiment, all fish were weighed to measure final average weight (g), survival (S), apparent feed conversion (AFC), specific growth rate (SGR), average productivity, (AP) weekly weight gain (WWG), protein efficacy rate (PER) and feed cost to produce 1,000 juveniles (C₁₀₀₀). The following equations were used to calculate the performance parameters:

S: survival (%);

FN: final number of animals;

IN: initial number of animals.

AFC: apparent feed conversion;

AF: total amount of feed provide (g);

FB: final biomass (g);

IB: initial biomass (g).

WWG: weekly weight gain (g day^-1):

FW: final weight (g);

IW: initial weight (g);

TW: experiment time in weeks.

SGR: specific growth rate (% day^-1);

IAW: initial average weight (g);

FAW: final average weight (g);

TD: experiment time in days.

AP: average productivity (kg m^-3);

FB: final biomass (kg);

V: volume (m³).

PER: protein efficiency rate;

WG: weight gain (g);

FC: feed consumption;

DCP: dietary crude protein (%).

C₁₀₀₀: feed cost to produce 1,000 juveniles;

FC: feed cost;

AFC: average food consumption.

Statical analysis

Data were submitted to the Kolmogorov-Smirnov test to verify whether the data distribution was within the normality curve and to the Levene test to verify homoscedasticity. The, the data were submitted to the t test (software STATISTICA 10.0). All analyzes with a significance level of 5% (Zar 2010ZAR JH. 2010. Biostatistical analysis. 5ª ed., Pearson Prentice Hall, 1-960 p.).

RESULTS

Growth performance, body indices and N and P retention

Fish fed with the control diet had higher final average weight, average daily gain, apparent feed efficiency, protein efficiency rate, specific growth rate, and cost per kilogram of fish compared to fish fed with taurine-supplemented diet (p < 0.05). Also, the productivity was higher in the tanks of the control treatment (p < 0.05). Fish survival was not influenced by diet (p > 0.05) (Table III).

Regarding body indices, fish fed with taurine-supplemented diet did not show significant changes (p > 0.05) in the evaluated parameters compared to the control treatment (Table III).

Nitrogen (N) retention was higher in fish fed the control diet (p < 0.05), while phosphorus (P) retention did not differ between treatments (p > 0.05) (Figure 1).

Animal health (hematology, immunology and experimental infection against Aeromonas hydrophila)

Among the hematological and immunological parameters evaluated, mean corpuscular volume (MCV) was lower in the treatment with taurine-supplemented diet (p < 0.05). The others parameters did not show significant differences between treatments (p < 0.05) (Table IV).

Survival after bacterial challenge also did not differ significantly between fish fed with taurine or not (p > 0.05) (Figure 2).

DISCUSSION

Experimental diets and physicochemical parameters of water quality

In this study, the experimental diets had similar centesimal composition and amino acid profiles. Of the evaluated amino acids, only methionine was below the recommended levels of 5.0 (Control) and 4.7 (Taurine) - 5.2 g kg^-1 (Furuya et al. 2010FURUYA WM, PEZZATO LE, BARROS MM, BOSCOLO WR, CYRINO JEP, FURUYA VRB & FEIDEN A. 2010. Tabelas brasileiras para a nutrição de tilápias. Toledo: GFM, 1-100 p.). However, about methionine + cysteine amount, only the taurine-supplemented diet was below the recommended level (9.2 g kg^-1), according to Furuya et al. (2010)FURUYA WM, PEZZATO LE, BARROS MM, BOSCOLO WR, CYRINO JEP, FURUYA VRB & FEIDEN A. 2010. Tabelas brasileiras para a nutrição de tilápias. Toledo: GFM, 1-100 p..

Methionine is the first limiting amino acid in diets formulated based on soy or soy derivatives (NRC 2011NRC - NATIONAL RESEARCH COUNCIL. 2011. Nutrient Requirements of Fish and Shrimp. Washington, DC: National Academy Press, 392 p. https://doi.org/10.17226/13039.
https://doi.org/10.17226/13039... ). In diets for tilapia juveniles using levels of methionine supplementation, lower weight gain was observed in fish fed with the lowest level of methionine inclusion (He et al. 2017HE JY, LONG WQ, HAN B, TIAN LX, YANG HJ, ZENG SL & LIU YJ. 2017. Effect of dietary L-methionine concentrations on growth performance, serum immune and antioxidative responses of juvenile Nile tilapia, Oreochromis niloticus. Aquac Res, 665-674 p., Urbich 2020URBICH AV. 2020. Desempenho produtivo, expressão de genes relacionados com o metabolismo de aminoácidos sulfurados e qualidade da carne de tilápias do Nilo na terminação, alimentadas com dietas suplementadas com metionina e taurina. Ponta Grossa, Tese de doutorado, Universidade Estadual de Ponta Grossa, 1-73 p.). Other studies have revealed similar data, with a low growth rate and high feed conversion in rainbow trout (Oncorhynchus mykiss) (Belghit et al. 2014BELGHIT I, SKIBA-CASSY S, GEURDEN I, DIAS K, SURGET A, KAUSHIK S, PANSERAT S & SEILIEZ I. 2014. Dietary methionine availability affects the main factors involved in muscle protein turnover in rainbow trout (Oncorhynchus mykiss). British Journal of Nutrition 112(4): 493-503.) and yellowtail (Seriola dorsalis) (Garcia-Organista et al. 2019GARCIA-ORGANISTA AA, MATA-SOTRES JA, VIANA MT & ROMBENSO AN. 2019. The effects of high dietary methionine and taurine are not equal in terms of growth and lipid metabolism of juvenile California Yellowtail (Seriola dorsalis). Aquaculture 512: 734304.), requiring the addition of this amino acid in crystalline form (Browdy et al. 2012BROWDY CL, BHARADWAJ AS, VENERO JA & NUNES AJP. 2012. Supplementation with 2-hydroxy-4-(methylthio)butanoic acid (HMTBa) in low fish meal diets for the white shrimp, Litopenaeus vannamei. Aquacult Nutr 18: 432-440., Michelato et al. 2018MICHELATO M, FURUYA WM, GATLIN III & DELBERT M. 2018. Metabolic responses of Nile tilapia Oreochromis niloticus to methionine and taurine supplementation. Aquaculture 485: 66-72., Nunes et al. 2014NUNES AJP, SÁ MV, BROWDY CL & VAZQUEZ-ANON M. 2014. Practical supplementation of shrimp and fish feeds with crystalline amino acids. Aquaculture 431: 20-27.). Therefore, growth performance is also correlated with methionine level in the diet, which, despite being below the recommended level for the species, good results can be justified by the sum of “methionine + cysteine”, because the data obtained in this research are similar to those of fish produced with a commercial diet (Stockhausen et al. 2022STOCKHAUSEN L, VILVERT MP, SILVA MD, DARTORA A, KRAINZ R, FERREIRA GB, DA SILVA LR & JATOBÁ A. 2022. Practical diet with total replacement of fishmeal by soybean meal for Nile tilapia: growth performance and health effects. Cienc Anim Bras 23: 71567.)

Growth performance, body indices and N and P retention

The life stage of the fish is a factor to be considered, as it has been observed in other studies, sometimes the need for taurine occurs in the early stages (post-larvae) (Al-Feky et al. 2014AL-FEKY SSA, EL-SAYED AFM & EZZAT AA. 2014. Dietary taurine improves reproductive performance of Nile tilapia (Oreochromis niloticus) broodstock. Aquacult Nutr 22(2): 392-399. doi:10.1111/anu.12256., Kim et al. 2005KIM S-K, TAKEUCHI T, YOKOYAMA M, MURATA Y, KANENIWA M & SAKAKURA Y. 2005. Effect of dietary taurine levels on growth and feeding behavior of juvenile Japanese flounder Paralichthys olivaceus. Aquaculture 250: 765-774., Salze et al. 2012SALZE G, MCLEAN E & CRAIG SR. 2012. Dietary taurine enhances growth and digestive enzyme activities in larval cobia. Aquaculture 362-363: 44-49.). According to Gonçalves et al. (2011)GONÇALVES GS, RIBEIRO MJP, VIDOTTI RM & SUSSEL FR. 2011. Taurine supplementation in diets for Nile tilápia Oreochromis niloticus. World Aquaculture, 6-10 p., it is difficult to draw distinctions based on feeding habits of the tilapia species already studied, for Nile tilapia taurine proves to be limiting, while for hybrid red tilapia, its requirement can be met by endogenous production.

Taurine supplementation (40.0 g kg^-1) did not improve the performance of tilapia over eight weeks in an experiment with soy-based diets when dietary methionine levels had not been achieved (Michelato et al. 2018MICHELATO M, FURUYA WM, GATLIN III & DELBERT M. 2018. Metabolic responses of Nile tilapia Oreochromis niloticus to methionine and taurine supplementation. Aquaculture 485: 66-72.). While in this study, the results showed that taurine supplementation compromised the performance of Nile tilapia juveniles. Considering the increased cost of the diet, the use of taurine was found to be unfeasible as a growth promoter. This result corroborates with Han et al. (2014)HAN Y, KOSHIO S, JIANG Z, REN T, ISHIKAWA M, YOKOYAMA S & GAO J. 2014. Interactive effects of dietary taurine and glutamine on growth performance, blood parameters and oxidative status of Japanese flounder Paralichthys olivaceus. Aquaculture 434: 348-354., who observed impaired growth performance in Red Drum (Sciaenops ocellatus) fed a diet supplemented with 1% and 2% taurine. However, even with a smaller effect on final weight gain and average daily gain, taurine did not influence fish survival rate.

Some studies have shown that taurine supplementation, when provided at levels above the optimal for the species, leads to excessive excretion to maintain its optimized metabolic concentration, which requires greater energy expenditure, thereby harming growth and gonadal development (Al-Feky et al. 2014AL-FEKY SSA, EL-SAYED AFM & EZZAT AA. 2014. Dietary taurine improves reproductive performance of Nile tilapia (Oreochromis niloticus) broodstock. Aquacult Nutr 22(2): 392-399. doi:10.1111/anu.12256., Yue et al. 2013YUE YR, LIU YJ, TIAN LX, GAN L, YANG HJ, LIANG GY & HE JY. 2013. The effect of dietary taurine supplementation on growth performance, feed utilization and taurine contents in tissues of juvenile White shrimp (Litopenaeus vannamei, Boone, 1931) fed with low-fishmeal diets. Aquac Res 44: 1317-1325.). Perhaps the dose offered to Nile tilapia juveniles in this study was above the recommended dose for juveniles, as this dose was based on the taurine requirement for the larval phase of tilapia obtained by Al-Feky et al. (2016)AL-FEKY SSA, EL-SAYED AFM & EZZAT AA. 2016. Dietary taurine enhances growth and feed utilization in larval Nile tilapia (Oreochromis niloticus) fed soybean meal-based diets. Aquacult Nutr 22(2): 457-464.. This fact would justify the low growth performance of fish fed a taurine-supplemented diet.

The same behavior has already been observed in silver catfish (Rhamdia quelen) by Martinelli (2016)MARTINELLI SG. 2016. Suplementação de taurina em dietas para Jundiá (Rhamdia quelen). Tese de Doutorado, Universidade Federal de Santa Maria, 1-94 p. and Rossato (2015)ROSSATO S. 2015. Estudo do desenvolvimento muscular e enzimático inicial do jundiá (Rhamdia quelen) com alimentos de origem animal e vegetal. Tese de Doutorado. Universidade Federal de Santa Maria, 1-182 p.. In the study of Martinelli (2016)MARTINELLI SG. 2016. Suplementação de taurina em dietas para Jundiá (Rhamdia quelen). Tese de Doutorado, Universidade Federal de Santa Maria, 1-94 p., silver catfish juveniles supplemented with 2% taurine had a worse feed conversion, negatively affecting productive parameters. Qi et al. (2012)QI G, AI Q, MAI K, XU W, LIUFU Z, YUN B & ZHOU H. 2012. Effects of dietary taurine supplementation to a casein-based diet on growth performance and taurine distribution in two sizes of juvenile turbot (Scophthalmus maximus L.). Aquaculture 358-359: 122-128. suggest that excessive taurine supplementation may retard growth through reduced fed intake. However, in silver catfish post-larvae fed diets based on soy protein concentrate and supplemented with 0.5% and 1.5% taurine, Rossato (2015)ROSSATO S. 2015. Estudo do desenvolvimento muscular e enzimático inicial do jundiá (Rhamdia quelen) com alimentos de origem animal e vegetal. Tese de Doutorado. Universidade Federal de Santa Maria, 1-182 p. observed a significant improvement in growth. Therefore, in the post-larval phase, the key enzyme in the conversion of cystine to taurine (L-cysteine sulfinate decarboxylase) is insufficiently produced to meet the metabolic demand for taurine, justifying the positive results obtained in the initial phase (Al-Feky et al. 2014AL-FEKY SSA, EL-SAYED AFM & EZZAT AA. 2014. Dietary taurine improves reproductive performance of Nile tilapia (Oreochromis niloticus) broodstock. Aquacult Nutr 22(2): 392-399. doi:10.1111/anu.12256., Salze et al. 2012SALZE G, MCLEAN E & CRAIG SR. 2012. Dietary taurine enhances growth and digestive enzyme activities in larval cobia. Aquaculture 362-363: 44-49.), different from the observed in this study.

The liver is a crucial organ for nutrient metabolism and is considered an excellent indicator of nutritional pathologies in fish. Its main functions include the formation of plasma proteins, deamination of proteins, formation of urea for ammonia removal, amino acid synthesis, and energy storage (Honorato et al. 2013HONORATO CA, ALMEIDA LC & MORAES G. 2013. Processamento da dieta – seus efeitos no aproveitamento de carboidratos para peixes. Revta Eletrôn Nutritime 10(5): 2700-2715.). The lipid storage and utilization cycle are usually associated with seasonal changes in food availability or metabolic demand (Soares et al. 2001SOARES MCF, URBINATI EC & MALHEIROS EB. 2001. Estocagem tecidual e utilização de lipídeos em Matrinxã, Brycon cephalus. ACTA Amazônica 31: 661-671.). Thus, the hepatosomatic index may be related to the mobilization of hepatic energy reserves necessary for vitellogenesis and reproduction, or lipid deposition in the liver in preparation for the winter period (Querol et al. 2002QUEROL MVM, QUEROL E & GOMES NNA. 2002. Fator de condição gonadal, índice hepatossomático e recrutamento como indicadores do período de reprodução de Loricariichthys platymetopon, bacia do rio Uruguai Médio, Sul do Brasil. Iheringia Sér Zool 92: 79-84.).

Regarding the hepatosomatic index, there were no significant differences between the diets. The increase in either treatment suggests a metabolic overload in the liver, which was not observed between the groups. These data differ from Urbich (2020)URBICH AV. 2020. Desempenho produtivo, expressão de genes relacionados com o metabolismo de aminoácidos sulfurados e qualidade da carne de tilápias do Nilo na terminação, alimentadas com dietas suplementadas com metionina e taurina. Ponta Grossa, Tese de doutorado, Universidade Estadual de Ponta Grossa, 1-73 p. in a study with Nile tilapia in the finishing phase in net tanks, which reported that fish fed diets supplemented with methionine (0.4%), taurine (0.5%), and methionine with taurine (0.4% + 0.5%), with low ether extract content (2.8%), had a lower hepatosomatic index. Similarly, in studies with other species, the inclusion of taurine resulted in a lower hepatosomatic index in yellowhead catfish (Pelteobagrus fulvidraco) (Li et al. 2016LI M, LAI H, LI Q, GONG S & WANG R. 2016. Effects of dietary taurine on growth, immunity and hyperammonemia in juvenile yellow catfish Pelteobagrus fulvidraco fed all-plant protein diets. Aquaculture 450: 349-355.), black carp (Mylopharyngodon piceus) (Zhang et al. 2018ZHANG J, HU Y, AI Q, MAO P, TIAN Q, ZHONG L, XIAO T & CHU W. 2018. Effect of dietary taurine supplementation on growth performance, digestive enzyme activities and antioxidant status of juvenile black carp (Mylopharyngodon piceus) fed with low fish meal diet. Aquac Res 49(9): 3187-3195.), and turbot (Scophthalmus maximus) (Liu et al. 2017LIU Y, YANG P, HU H, LI Y, DAI J, ZHANG Y, AI Q, XU W, ZHANG W & MAI K. 2017. The tolerance and safety assessment of taurine as additive in a marine carnivorous fish, Scophthalmus maximus L. Aquacult Nutr 24(1): 461-471.).

Fish with higher energy reserves have a greater adaptation to the cold in order to maintain their fluidity in winter, and the most significant response to this stress is the increase in levels of unsaturated fatty acids in the bloodstream that originate from the liver, as observed by Ribeiro et al. (2012)RIBEIRO CS, GOMES AD, VIEIRA VARO, TABATA YA, TAKAHASHI NS & MOREIRA RG. 2012. The effect of ploidy on the fatty acid profile during the reproductive cycle of female rainbow trout (Oncorhynchus mykiss). Aquacult Int 20: 1117-1137. in carp (Cyprinus carpio) and rainbow trout (Oncorhynchus mykiss). Therefore, taurine supplementation may be a study topic to stimulate an increase in energy reserves in tilapia for the winter season. However, in this study, temperatures were maintained at optimal levels for the species, justifying once again the unsatisfactory results of taurine supplementation for juvenile tilapia under this condition.

The ratio weight: body length allows for the calculation of a parameter that determines the degree of well-being of the fish, called the condition factor (K). K is an important indicator of an individual’s health status, and its value reflects recent nutritional conditions and/or the use of reserves in cyclic activities, making it possible to relate it to environmental conditions and behavioral aspects of the species (Gomiero et al. 2010GOMIERO LM, VILLARES-JUNIOR GA & BRAGA FMS. 2010. Relação peso-comprimento e fator de condição de Oligosarcus hepsetus (Cuvier, 1829) no Parque Estadual da Serra do Mar - Núcleo Santa Virgínia, Mata Atlântica, estado de São Paulo, Brasil. Biota Neotropica 10(1): 101-105.). The similarity in K of the fish suggested normality in the data, regardless of supplementation or not.

Excessive concentrations of nutrients such as N and P can lead to eutrophication of the environment, compromising the water quality and support capacity of aquaculture systems (English et al. 1993ENGLISH WR, SCHWEDLER TE & DYCK LA. 1993. Aphanizomenon flos-aquae, a toxic blue green alga in commercial channel catfish, Ictalurus punctatus, ponds: a case history. J Appl Aquac 3: 195-209., Van Der Ploeg & Boyd 1991VAN DER PLOEG M & BOYD CE. 1991. Geosmin production by cyanobacteria (blue green algae) in fish ponds at Auburn, Alabama. J World Aquac Soc 22: 207-216.). Excessive nitrogenous compounds are toxic to fish and can affect the organoleptic characteristics of the meat. Among toxic compounds, ammonia is the product of protein catabolism in fish, which comprises about 80% of total nitrogen excretion by fish, and its excretion rate is influenced by various factors, such as the quantity and quality of feed (Chakraborty & Chakraborty 1998CHAKRABORTY SC & CHAKRABORTY S. 1998. Effect of dietary protein level on excretion of ammonia in Indian major carp (Labeo rohita), fingerlings. Aquacult Nutr 4: 47-51.). Due to the reduced retention of nitrogen in fish, the use of taurine at the evaluated level may present a potential pollutant for open production systems, although no difference was observed in water quality variables. Furthermore, the lower retention of amino acids results in lower protein deposition and increased production and excretion costs of nitrogen, reducing fish growth (Furuya et al. 2001FURUYA WM, PEZZATO LE, PEZZATO AC, BARROS MM & MIRANDA ECD. 2001. Coeficientes de Digestibilidade e Valores de Aminoácidos Digestíveis de Alguns Ingredientes para Tilápia do Nilo (Oreochromis niloticus). R Bras Zootec 30(4): 1143-1149., Bureau & Encarnação 2006BUREAU DP & ENCARNAÇÃO PM. 2006. Adequately defining the amino acid requirements of fish: the case example of lysine. In: SIMPOSIUM INTERNACIONAL DE NUTRICIÓN ACUÍCOLA, AVANCES EN NUTRICIÓN ACUÍCOLA, 8, p. 29-54, Monterrey.), which may be another reason for the low productive performance of tilapia fed taurine-supplemented diets.

Animal health (hematology, immunology and experimental infection against Aeromonas hydrophila)

Fish are known to be in close relationship with the environment in which they live, so blood reveals internal body condition even before there is visible clinical manifestation (Barbieri & Bondioli 2013BARBIERI E & BONDIOLI ACV. 2013. Acute toxicity of ammonia in Pacu fish (Piaractus mesopotamicus, Holmberg, 1887) at different temperatures levels. Aquac Res 46(3): 565-571., Musa & Omoregie 1999MUSA SO & OMOREGIE E. 1999. Haematological changes in the mud fish Clarias gariepinus exposed to malachite green. Journal of Aquatic Sciences 14: 37-47., Okechukwu et al. 2007OKECHUKWU EO, ANSA J & BALOGUN JK. 2007. Effects of acute nominal doses of chlorpyrifos-ethyl on some haematological indices of African catfish Clarias gariepinus. J Fish Int 2: 190-194.). The use of hematological and immunological parameters in the evaluation of fish physiology has been increasingly recognized as a tool for assessing animal health status, with the purpose of detecting functional alterations in response to various stress conditions (Satake et al. 2009SATAKE F, PÁDUA SB & ISHIKAWA MM. 2009. Distúrbios morfológicos em células sanguíneas de peixes em cultivo: uma ferramenta prognóstica. In: SATAKE F, PÁDUA SB & ISHIKAWA MM, Distúrbios morfológicos em células sanguíneas de peixes em cultivo: uma ferramenta prognóstica. In: TAVARES-DIAS M. Manejo e sanidade de peixes em cultivo. 1 ed., Macapá: Embrapa Amapá, 330-345., Schutt et al. 1997SCHUTT DA, LEHMANN J, GUERLICH R & HAMERS R. 1997. Haemotology of swondtail Xiphiphorus helleri 1: Blood parameters and light microscopy of blood cells. Journal Applied Ichthyology 13: 83-89., Yousefi et al. 2022YOUSEFI M, HOSEINI SM, WEBER RA, DA SILVA E, RAJABIESTERABADI H, ARGHIDEH M & DELAVAR FH. 2022. Alleviation of transportation-induced stress in Nile tilapia, Oreochromis niloticus, using brackish water. Aquaculture Reports 27: 101378.), with quite reliable results (Katalog & Parlak 2004KATALOG S & PARLAK H. 2004. The effects of pollution on haematological parameters of Black goby in foca and aliaga boys. E.U. Journal of Fisheries and Aquatic Sciences 21: 113-117.). Additionally, hematological and immunological analyses are currently used to evaluate the effect of feed additives (prebiotics, probiotics, organic acids, among others) on the health of aquatic animals (Dawoo et al. 2020, Hassaan et al. 2018HASSAAN MS, SOLTAN MA, JARMOŁOWICZ S & ABDO HS. 2018. Combined effects of dietary malic acid and Bacillus subtilis on growth, gut microbiota and blood parameters of Nile tilapia (Oreochromis niloticus). Aquacult Nutr 24(1): 83-93., Jatobá et al. 2011JATOBÁ A, VIEIRA FN, BUGLIONE-NETO CC, MOURIÑO JLP, SILVA BC, SEIFTTER WQ & ANDREATTA ER. 2011. Diet supplemented with probiotic for Nile tilápia in polyculture system with marine shrimp. Fish Physiol Biochem 37: 725-732., 2018, Mendoza Rodriguez et al. 2017MENDOZA RODRIGUEZ MG, POHLENZ C & GATLIN III DM. 2017. Supplementation of organic acids and algae extracts in the diet of red drum Sciaenops ocellatus: immunological impacts. Aquac Res 48(4): 1778-1786., Moraes et al. 2018MORAES AVD, PEREIRA MDO, MORAES KN, RODRIGUES-SOARES JP, JESUS GFA & JATOBA A. 2018. Autochthonous probiotic as growth promoter and immunomodulator for Astyanax bimaculatus cultured in water recirculation system. Aquac Res 49(8): 2808-2814.). However, there are no records of hematological analyses in tilapia supplemented with taurine.

Blood parameters are considered indicators of the healthy status and physiological conditions of fish (Kader et al. 2010KADER MA, KOSHIO S, ISHIKAWA M, YOKOYAMA S & BULBUL M. 2010. Supplemental effects of some crude ingredients in improving nutritive values of low fishmeal diets for red sea bream, Pagrus major. Aquaculture 308(3-4): 136-144.). In this study, the blood parameters of the fish were within the range considered healthy for the species (Barros et al. 2009BARROS MM, RANZANI-PAIVA MJT, PEZZATO LE, FALCON DR & GUIMARAES IG. 2009. Haematological response and growth performance of Nile tilapia (Oreochromis niloticus L.) fed diets containing folic acid. Aquac Res 40: 895-903., 2015, Weiss & Wardrop 2010WEISS DJ & WARDROP KJ. 2010. Schalm’s Veterinary Haematology. 6ª ed., Blackwell Publishing, 1-1909 p.) and were not altered by the inclusion of taurine, except for the MCV index in the fish from the control treatment. This data, if associated with low hematocrit, could indicate the occurrence of microcytic hypochromic anemia in the animals. However, since the hematocrit level in this treatment did not show a significant difference, and the total count of erythrocytes was higher, it indicates an intensification of erythropoiesis, with a greater amount of young circulating red blood cells.

These results are consistent with Han et al. (2014)HAN Y, KOSHIO S, JIANG Z, REN T, ISHIKAWA M, YOKOYAMA S & GAO J. 2014. Interactive effects of dietary taurine and glutamine on growth performance, blood parameters and oxidative status of Japanese flounder Paralichthys olivaceus. Aquaculture 434: 348-354. who did not observe hematological alterations in red drum (Sciaenops ocellatus) fed a diet supplemented with taurine, however, the authors stated that the supplementation of this amino acid promoted resistance to oxidative stress. As for Nile tilapia, taurine plays an important role during the adaptation of tilapia to high salinity water (Takeuchi et al. 2000TAKEUCHI K, TOYOHARA H, KINOSHITA M & SAKAGUCHI M. 2000. Ubiquitous increase in taurine transporter mRNA in tissues of tilapia (Oreochromis mossambicus) during high-salinity adaptation. Fish Physiol Biochem 23(2): 173-182.).

As well as hematological and immunological analyses, experimental infections are commonly used to evaluate feed additives, as animal growth and health performance have a direct relationship. In this study, after experimental infection with Aeromonas hydrophila, the survival rate did not differ between treatments, corroborating with the hemato-immunological data and survival during cultivation, suggesting that taurine supplementation does not influence the animal health against bacterial infections.

To summarize, the inclusion of 9.7 g kg^-1 of taurine in a plant-based diet compromised the growth performance and increased production costs of Nile tilapia (O. niloticus) juveniles. However, it did not affect their health. Additionally, this supplementation resulted in an increased potential for pollution due to reduced nitrogen retention. Therefore, further research is needed to assess the feasibility of supplementing Nile tilapia with different levels of taurine at various life stages and under different environmental conditions, such as the BFT.

ACKNOWLEDGMENTS

We acknowledge the scholarhips provide by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) and NUTRICOL® for proving the formulated diets.

REFERENCES

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