Optimal Feeding Frequency for African Sneakhead Fish (Parachanna obscura, Gunther, 1861) Fingerlings Reared in Captivity

Parachanna obscura is a fish that has a good economic value and is an important performance for aquaculture. By identifying the optimum stocking density and frequency of feeding, farmers can successfully decrease the feed charge and increase growth performance. The aim of our study is to define optimum frequency of feeding of P. obscura fingerlings reared controlled condition. Therefore the experiment was conducted during three months. The fingerlings of P. obscura were fed one of four schedules at 3% of body weight. The initial weight body was 13.27±0.07 g. At the end of this study, the results prove that survival rates were 100% and were not significantly affected by the frequency of feeding (p˃0.05). Growth performances varied significantly with treatments (p<0.05). The augmentation of frequency of feeding above 3 times/day did not produce any significant (p˃0.05) improvement of growth. Therefore, optimal feeding frequency for Parachanna obscura fingerlings reared in controlled conditions is three times daily.


Background
The snakehead belonging to the family Channidae is one of the important native fish of freshwater of tropical Africa and Asia (Ng and Lim, 1990). The local and international markets greatly demand on Channidae due to its tasty flesh and medicinal value in enhancing wound healing and reducing potsoperative pain (Mollah et al., 2009). Parachanna obscura is the most common African Channidae (Bonou and Teugels, 1985). It is a hardy species that supports stressful conditions (Kpoguè et al., 2013a). It has good economic value and is an important performance for aquaculture (Micha, 1974;Boladji et al., 2011). It is not a fatty fish but an intermediate one (Mujina et al., 2009). It is consumed for its nutritional value (Ama-Abasi and Ogar, 2013) and its flesh is white, firm, practically boneless and has an good flavor. To maintain this fish population as well as its rehabilitation and conservation, development of a suitable technology for rearing of P. obscura fingerlings is necessary. Efforts on culturing P. obscura merely start and end at collecting them from the wild. It is reared in small reservoirs in hydroagricultural purpose in Ivory Cost (Lazard and Legendre, 1994). It is also extensively cultured in Cameroon, Nigeria and Democratic Republic of Congo (De Graaf, 2004;FAO, 2007;Bassey and Ajah, 2010). In intensive fingerlings culture, several factors influence survival rate, welfare, growth, feed efficiency, production including feeding level (El-Sayed, 2002;Imtiaz, 2007), dietary nutrient level (NRC, 1993), stocking density (Ma et al., 2006;Chambel et al., 2015;Gao et al., 2017) and feeding frequency (Jamabo et al., 2015). The overfeeding of fish pollutes the water of the aquaculture and meant expenses supplement on the production cost. However, the optimization of the feed ration and the frequency of distribution constitute fields of research in the aquaculture. In aquaculture, stocking density is the concentration which fish are stocked into a system (De Oliveira et al., 2012). By identifying the optimum stocking density and feeding frequency, farmers can successfully decrease the feed cost and increase growth and also able to manage other parameters such as variation of individual size and qualities of water which are deemed important in rearing of fish in culture conditions. Feeding level requirements, dietary (protein, lipid and carbohydrate) level requirements of P. obscura fingerlings have been determined by (Kpoguè and Fiogbé , 2012;Kpoguè et al., 2013b;Kpoguè et al., 2018a;Kpoguè et al., 2018b). No work has yet been undertaken on feeding frequency of P. obscura fingerlings. The aim of study is therefore to determine optimum frequency of feeding of P. obscura fingerlings reared controlled condition.

Results
During the experimental, physico-chemical parameters are 27.85 ± 0.29°C for the temperature, 6.57 ± 0.16 mg/L for the dissolved oxygen and 6.15 ± 0.82 for pH. Survival rate, growth performances (condition factor, specific growth rate and final body weight) and feed efficiency during the study are presented in Table 1. There was no mortality recorded during the experiment period. Survival rate didn't vary among treatments and was 100% (p˃0.05). Growth performances varied significantly with treatments (p<0.05). Thus the greatest final body weight was achieved by the fish fed treatments T2 (3 times/day), T3 (4 times/day) and T4 (5 times/day). The least final body weight (26.75±0.86 g) was recorded with fish fed treatment T1 (2 times/day). The specific growth rate and the condition factor improved significantly (p<0.05) as feeding frequency increased from twice (T1) for 3 times/day (T2). The augmentation of feeding frequency above 3 times/day did not produce any significant (p˃0.05) improvement of specific growth rate ( Figure 1). Feed efficiency did not varied significantly with treatment (p˃0.05). Nevertheless, it varied from 0.51 ± 0.05 (T1) to 0.63 ± 0.12 (T3). 100±0.00 a 100±0.00 a 100±0.00 a 100±0.00 a Figure 1 Relationship between specific growth rate and feeding frequency

Discussion
The mean quality of water parameters values (dissolved oxygen, pH temperature) observed in this study were within the recommended range for P. obscura according to Bonou and Teugels (1985) and Riehl and Baensch (1991). Feeding and feeding frequencies are key factors that determine the growth and survival chances of fishes (Ndome et al., 2011). Multiple feedings has previously been found to be stimulatory for growth, survival and feed utilization in fingerlings of Indian major carps (Choudhury et al., 2002;Kiaalvandi et al., 2011;Ashfauq et al., 2017). The results of our study showed that, in any treatments, a survival rate (100%) was affected by the feeding frequency. These results confirmed that P. obscura is a hardy and rustic species (Kpoguè et al., 2013a). Growth performances (final body weight, specific growth rate and condition factor) varied significantly with treatment. But the augmentation of feeding frequency above 3 times/day did not produce any significant (p˃0.05) improvement of growth. The least growth performances were recorded in fingerlings fed with twice/day groups.
Growth generally increased with feeding frequency up to a given limit (Wang et al., 1998;Bascinar et al., 2007;Asuwaju et al., 2014;Jamabo et al., 2015). Indeed, according to several studies, the schedules of feed strongly affect the ingestion and the assimilation of feed. The fish which are less frequently fed can adapt to such conditions by consuming greater quantities of feed during each feeding. If schedules are applied for a long period, this can lead to the hyperphagia. The fish which are well fed more frequently consume a greater quantity of; while feed, when the intervals between the meals are short, feed crosses the digestive area more quickly, having for result an ineffective digestion. Feed efficiency did not varied significantly with treatment (p˃0.05). Nevertheless, it varied from 0.51±0.05 (T1) to 0.63±0.12 (T3). This result was an indication of better food utilization efficiency when feeding frequency is thrice time daily. According to Jamabo et al. (2015), feeding frequency is optimal for the condition of the trial suggesting that both growth parameters and feed utilization are most efficiency. Therefore, optimal feeding frequency for Parachanna obscura fingerlings reared in controlled conditions is three times daily. This observation agrees with the findings of several authors. According to Abid and Ahmed (2009) and Aderolu et al. (2010), optimum feeding frequency of Labeo rohita and Clarias gariepinus fingerlings is three times daily respectively. Moreover, three feeding a day have been found to be sufficient for maximum growth of Oncorhynchus mykiss (Ruohonen et al., 1998).

Fish and experimental design
The experiment was conducted in the experimental Station in the Wetlands Research Unit of Faculty of Abomey Calavi University (6°25'1.53''N, 2°20'42.2''E). 300 fingerlings of Parachanna obscura (mean weight: 13.27 ± 0.07 g) were collected in a pond on the experimental station. They were stocked per a 225 liter tank for 12 weeks. Water was continuously renewed (1 L/min). Tanks were protected at half with a perforated wooden plank to avoid fish from jumping out. Based on nutrient of various ingredients composition (Table 2), experimental diet was formulated (Table 3) and used during the trial. Sulfate of ferrous was used to decrease a possible toxicity of free gossypol in the diet. The ingredients diet were ground, weighted and mixed. Feed preparation was made by mixing the ingredients with boiling water and oil in paste. The paste was transformed into pellets of 2 mm diameter by food blender. After freeze drying at a temperature of 28 to 35°C in lyophilisator, the pellets were manually broken in small pieces. The fishes were fed one of four schedules (Table 4) at 3% of body weight (Kpoguè and Fiogbé , 2012) from 08:00 AM to 08:00 PM up to apparent satiation. Each treatment was tested in triplicate. The density of 50 fishes/tank was used. Physico-chemical parameters of water were measured during the experiment period. A portable chemical multimeter parameters served to measure temperature, pH and dissolved oxygen.
Test fishing was carried every seven days. Ponds were emptied and washed. Fishes were counted and weighted per pond. Test fishing enabled ration readjusting in relation to biomass. At the end of experiment, biomass, total fries number, weight and individual length were measure in each pond.

Chemicals and calculations
Standard methods for dry matter were used to analyze the ingredients and diet samples. The (oven drying) at 105°C for 24 h, crude protein (CP) (N-Kjeldahl×6.25) and ash (oven incineration at 550°C for 12 h) were used. Lipids were extracted according to Bligh and Dyer (1959). Analysis of the amino acids in the ingredients was carried out by high performance liquid chromatography (HPLC, Waters 474, Milford, MA, USA). These analyses were carried out according to the method described by Alegria et al. (1999). Whereas gossypol was determined according to the method described by Imorou Toko et al. (2008), phytic acid in the ingredients was acid-extracted using 3% H 2 SO 4 for 60 min at room temperature, centri-fuged at 3,897 g for 15 min. Supernatant was mixed with FeCl 3 (0.1 N) and centrifuged again to obtain a precipitate at which we added de-ionized water and NaOH (1.5 N) to extract the phytate after incubation at 80°C during 30 min. After the feeding trial, fish were collected, counted, weighed and the different parameters were calculated as follows: Where: FN = final fish number per pond, IN = initial fish number per pond, FB = final biomass per pond, Ln = logarithm, T = time (experiment duration), DB = dead fish biomass (g), IB = initial biomass per pond (g), DR = distributed ration (g).

Statistical analysis
Data collected during experiment were encoded in Excel software version 2010. Different zootechnical parameters, physico-chemical and morpho-metrical were calculated. Mean and range of each parameter were calculated and graphs were drawn. Statistical analyses were carried out by using STATVIEW software (version 5.01) at 5% probability threshold. A one way analysis of variance was carried out to compare zootechnical performances of different treatments. In case of significant differences, the Fisher LSD (Least Significant Difference) test served to means comparisons.

Conclusion
Fixing the optimum frequency of feeding, farmers can decrease the feed cost and increase growth parameters. This study showed that the augmentation of feeding frequency above 3 times/day did not produce any significant improvement of growth. Therefore, optimal feeding frequency for Parachanna obscura fingerlings reared in controlled conditions is three times daily.