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Shrimp extract (ShE) is one kind of aquatic animal attractant with abundant amino acids. In order to investigate the effects of dietary ShE supplementation on the growth and muscle fatty acid of juvenile red tilapia (initial weight: 12.02 ± 0.02 g), a 62‐day experiment was conducted. The fish were fed six diets containing graded levels of ShE (0%, 0.5%, 1%, 2%, and 3%) without fish meal (FM) and an FM diet in triplicate groups. At the end of the experiment, the final body weight, weight gain, specific growth rate, and feed intake of the red tilapia fed the 3% ShE diet and FM diet were significantly higher than those fed the other diets (p <.05). The total saturated fatty acid of fish muscle in the ShE diet groups was lower than that in the FM diet group (p <.05). The contents of erucic acid (C22:1), eicosapentaenoic acid (C20:5 n‐3; EPA), docosapentanoic acid (C22:5 n‐3; DPA), and docosahexaenoic acid (C22:6 n‐3; DHA) in the ShE diet groups were also lower than those in the FM diet group (p <.05). The expression level of the lpl gene in red tilapia liver of experimental group was significantly higher than that of the control group (p <.05). The liver mdh gene mRNA expression levels were higher in the red tilapia fed 0.5%, 2%, and 3% ShE diets than those of other groups (p <.05). Moreover, the respiratory burst activity had a positive effect in the 0.5%, 1%, and 2% ShE diet groups (p <.05). Our results suggest that dietary ShE has a significant effect on the growth and lipid metabolism‐related genes of fish, and 3% ShE was recommended to be supplemented in juvenile red tilapia diets. [ABSTRACT FROM AUTHOR]

A 68-day experiment was conducted to investigate the effects of dietary cystine (Cys) and tyrosine (Tyr) on skin melanogenesis pathways in Malaysian red tilapia (initial weight: 15.04 ± 0.03 g). Six practical diets containing extra 0.1%, 0.5%, 1% cystine (Cys) and 0.5%, 1%, 2% tyrosine (Tyr) based on the control diet were prepared, accordingly named as Control, Cys-0.1%, Cys-0.5%, Cys-1%, Tyr-0.5%, Tyr-1% and Tyr-2% respectively. Each diet was fed to triplicate groups of fish during the trial. At the end of the experiment, the final weight for each group was not significantly different ( P  > 0.05). However, the dietary Cys and Tyr had significant effects on the melanin level and tyrosinase activity in the skin of fish. The melanin content in the skin of fish was lowest in Cys-0.5% group, with a higher level observed at Cys-0.1% and Cys-1% group. The final melanin of fish skin in Cys-1% was higher than that in Cys-0.5% and Cys-0.1% ( P  < 0.05). At the end of the experiment, the melanin in ventral skin of fish in Tyr-2% was higher than that in Tyr-0.5% and Tyr-1% ( P  < 0.05), and the melanin in dorsal skin of fish in Tyr-0.5% was lower than that in Tyr-1% and Tyr-2% ( P  < 0.05). The final tyrosinase activity of fish skin in Cys-1% was highest, and the final tyrosinase activity in Tyr-1% and Tyr-2% were significantly higher than that in Tyr-0.5% ( P  < 0.05). In serum, the tyrosinase activity was highest in Cys-1%, and the tyrosinase activity in Tyr-2% was significantly higher than that in Tyr-1% and Tyr-0.5% ( P  < 0.05). Moreover, the ventral skin melanin zone in Cys-1% treatment is largest by slice microstructure observation. The expression of tyrosinase mRNA in Tyr-2% group was highest in ventral skin of fish. At the end of the experiment, tyrosinase mRNA in the dorsal skin of fish was lowest in Cys-0.5%, with a higher level observed at Cys-0.1% and Cys-1% group. The final expression of tyrosinase mRNA in Tyr-0.5% was lower than that in Tyr-1% and Tyr-2% in dorsal skin of fish ( P  < 0.05). The final expressions of slc7a11 mRNA in Tyr-1% was higher than that in Tyr-0.5% in dorsal skin of fish ( P  < 0.05). Present results demonstrated that dietary Cys and Tyr could affect the melanin synthesis pathway in the red tilapia. [ABSTRACT FROM AUTHOR]

The effects of changes in background color, between white and black, on the apparent body color, the skin L*, a* and b* values, the MSH levels in the serum and the melanin-concentrating hormone (mch), proopiomelanocortin (pomc), melanocortin 1 receptor (mc1r) and tyrosinase (tyr) gene mRNA expressions of Malaysia red tilapia were investigated. After rearing in black (B) or white (W) background tanks for 27 days, the rest fishes were transferred to the same (WW and BB) or opposite (WB and BW) background tanks for another 27 days. The apparent body color of fish was paler in white background and darker in black background, and the body color was reversibly variable in response to transfer to the opposite background color. Correspondingly, the L* and b* values were higher and a* values were lower in white background groups than that in black background groups in the skin of fish (P <.05). The expression of mch gene mRNA in the brain were higher in W fish than in B fish (P <.05). In contrast, the pomc mRNA levels were higher in B group than that in W group in the pituitary of fish (P <.05). However, the MSH levels in the serum of fish were not significantly different between W and B group (P >.05) and peaked in WW group (P <.05). Interestingly, the expressions of pomc in pituitary, mc1r and tyr in dorsal skin of fish on day 27 were higher than that on day 54 (P <.05). The mc1r mRNA expressions in the skin of W and B fish were not significantly different (P >.05). However, BB fish showed significantly higher skin mc1r mRNA expressions than WW and BW fish (P <.05). The tyr mRNA in the ventral skin of red tilapia was highest in B group. And the expression of tyr mRNA in BB group was higher than that in BW, WW and WB groups in the skin of fish (P <.05). Present results will facilitate understanding the mechanism of fish skin color determination. • Fish exhibits reversible body color change with black or white background adaptation. • The L*, a* and b* values are an effective indicator for apparent body color of fish. • The expression of mch and pomc are opposite in response to background color changes. • The serum MSH levels were not different between W and B group and peaked in WW group. • The expression of pomc , mc1r and tyr may be associated with the synthesis of melanin. [ABSTRACT FROM AUTHOR]

Red tilapia has become more popular for aquaculture production in China in recent years. However, the pigmentation differentiation that has resulted from the process of genetic breeding and skin color variation during the overwintering period are the main problems limiting the development of commercial culture. The genetic basis of skin color differentiation is still not understood. Solute carrier family 7 member 11 (slc7a11) has been identified to be a critical genetic regulator of pheomelanin synthesis in the skin of mammals. However, little information is available about its molecular characteristics, expression, location and function in skin color differentiation of fish. In this study, three complete cDNA sequences (2159 bp, 2190 bp and 2249 bp) of slc7a11 were successfully isolated from Malaysian red tilapia, encoding polypeptides of 492, 525 and 492 amino acids respectively. Quantitative real-time PCR demonstrated that slc7a11 mRNA expression is high in the ventral skin of PR (pink with scattered red spots) fish. Immunofluorescence analysis revealed that xCT (the protein encoded by slc7a11) was concentrated mainly in the cytoplasm and nucleus of both the dorsal and ventral skin cells of fish. After RNA interference of slc7a11 , slc7a11 and cbs mRNA expressions decreased, but the tyr mRNA expression increased in the skin of fish. Results suggest that slc7a11 plays an important role in skin color formation and differentiation of red tilapia through the melanogenesis pathway. • Three full-length cDNA of slc7a11 were identified from Malaysia red tilapia. • slc7a11 mRNA expressions were high in the ventral skin of PR fish. • SLC7A11 was concentrated mainly in the cytoplasm and nucleu of fish skin. • The cbs mRNA expression decreased and tyr expression increased after slc7a11 RNAi. • slc7a11 plays important role in skin color differentiation through the melanogenesis pathways. [ABSTRACT FROM AUTHOR]