Elsevier

Fish & Shellfish Immunology

Volume 75, April 2018, Pages 158-163
Fish & Shellfish Immunology

Full length article
Effects of l-tryptophan on the growth, intestinal enzyme activities and non-specific immune response of sea cucumber (Apostichopus japonicus Selenka) exposed to crowding stress

https://doi.org/10.1016/j.fsi.2018.01.009Get rights and content

Highlights

  • Crowding stress of A. japonicus was mitigated by dietary L-tryptophan.

  • The SGRs were significantly higher in the animals fed the diet with 3% Trp.

  • 3% dietary Trp was able to enhance intestinal enzyme activities of sea cucumber.

  • 3% dietary Trp also enhance non-specific immune response of the animals.

Abstract

In order to reveal the effects of l-tryptophan (Trp) on the physiology and immune response of sea cucumber (Apostichopus japonicus Selenka) exposed to crowding stress, four density groups of sea cucumbers (i.e. 4, 8, 16 and 32 individuals per 40 L water, represented as L, ML, MH and H) were fed with diets containing 0, 1, 3 and 5% l-tryptophan respectively for 75 days. The results showed that the specific growth rates (SGR) of the sea cucumber fed with diet with 3% Trp (L, 2.1; ML, 1.76; MH, 1.2; H, 0.7) were significantly higher than those fed with basal diet without Trp supplementation (P < .05). Peak amylase activity occurred at H stress density at 3% dietary Trp. Trypsin activity was higher in diet 3% in ML and MH densities than the controls, which increased by 66.4% and 53.8%. However, the lipase activity first increased and then decreased from the stocking density L to H, with highest values of 3% Trp group showed the highest value than other groups. Compared to those fed with the basal diet, sea cucumber fed diets with Trp (3%) had significantly higher phagocytic activities (0.28 OD540/106 cells, H) in coelomic fluid and respiratory burst activities (0.105 OD630/106 cells, MH) (P < .05). The results suggested that Trp cannot improve superoxide dismutase (SOD) activity at L, ML and MH densities. The alkaline phosphatase activity (AKP) significantly decreased at H stress density. Under the experimental conditions, the present results confirmed that a diet supplemented with 3% Trp was able to enhance intestinal enzyme activities, non-specific immune response and higher growth performance of A. japonicus.

Introduction

Sea cucumber Apostichopus japonicus Selenka used as tonic and a traditional medicine essential for keeping humans healthy, which was higher in protein and lower in fat than most foods [[1], [2], [3]]. As an economically important farmed species, its production exceeded 200, 969 t in China in 2014 [4]. However, crowding stress has attracted much attention in intensive culture practice [5,6]. High stocking density can suppress appetite [7,8] and growth of the animal [9,10]. Other serious consequences of crowding stress were immune suppression and higher susceptibility to pathogens [[11], [12], [13]].

Nutritional adjustment is one of the promising manipulations to improve fish ability in resisting stress [[14], [15], [16]]. The amino acid tryptophan is an essential component of animal feed [17,18]. While Trp serves as the immediate precursor for serotonin synthesis [19] can promote animal growth and protein synthesis, affect the animal's behavior and food intake [20]. Supplementing Trp through diet has been shown to suppress the neuroendocrine stress response in vertebrates including fish [[21], [22], [23], [24]] and other animals [25,26], including humans [27]. Furthermore, dietary Trp has been associated with the control of immune response [28]. The accessibility of nutrients from a particular food source is mainly determined by the profile and activity of the organism's digestive enzymes [29,30]. The study of digestive enzyme activity is an essential step toward understanding digestion and nutritional needs [18,31].

There is little information on the relationship between stress and dietary nutrient in invertebrate sea cucumber A. japonicus Selenka, which belongs to Echinodermata. A. japonicus Selenka without acquired immune system, coelomocytes are the major line of defense. Therefore, the present study is designed to determine the effects of dietary Trp on relieving of crowding stress of sea cucumber A. japonicus.

Section snippets

Experimental diets

The brown alga Sargassum thunbergii powder was used as the main sources of the basal diet. The ingredients of basal diet involved S. thunbergii (70%), sea mud (20%), fish meal (10%), which contained ash (59.90%), crude protein (16.56%), crude lipid (8.52%) and its energy content was 6.67 kJ g−1. The diets were formulated to contain four graded levels of tryptophan(0, 1, 3 and 5%, respectively). The final tryptophan contents of each diet were 0.15, 1.12, 3.11 and 5.10%, respectively. l

Growth performance

The growth performance differed significantly among A. japonicus fed the different diets at different stocking density (Table 1). Sea cucumbers fed diet supplement with 3% Trp had the highest SGR in each density groups (L, 2.1; ML, 1.76; MH, 1.2; H, 0.7), whereas A. japonicus fed the basal diet without try had the lowest SGR (P < .05) (Table 1) (Table 2).

Digestive enzyme activity

The digestive enzyme parameters differed significantly among A. japonicus fed the different trypthan diets. Dietary Trp had no significant

Discussion

In the crowding stress experiment, A. japonicus in low density group has high body growth rate. The SGR of the A. japonicus decreased as the stocking density increased in the experiment. In the present study, sea cucumbers fed tryptophan exhibited improvement in growth compared to animals fed the basal diet. Similar results had been observed in Catla catla [34], silvercatfish Rhamdia quelen [20] and sea bass (Dicentrarchus labrax) [35]. Li et al. [36] suggested that diet supplementation with

Conclusions

The present result proved that growth and immune suppression were the serious consequences of crowding stress. Dietary supplementation of tryptophan could significantly increase SGR, digestive enzyme activity of intestine and energy allocation for growth, enhance immune response at a certain extent, and augment the growth of sea cucumber.

Acknowledgments

This work was supported by the National Key R & D Program (2011BAD13B03), National Natural Science Foundation of China (30771661) and National Marine Public Welfare Project of China (200905020).

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