Wilson Pinto

Cloning, tissue and ontogenetic expression of the taurine transporter in the flatfish Senegalese sole (Solea senegalensis)

Flatfish species seem to require dietary taurine for normal growth and development. Although dietary taurine supplementation has been recommended for flatfish, little is known about the mechanisms of taurine absorption in the digestive tract of flatfish throughout ontogeny. This study described the cloning and ontogenetic expression of the taurine transporter (TauT) in the flatfish Senegalese sole (Solea senegalensis). Results showed a high similarity between TauT in Senegalese sole and other vertebrates, but a change in TauT amino acid sequences indicates that taurine transport may differ between mammals and fish, reptiles or birds. Moreover, results showed that Senegalese sole metamorphosis is an important developmental trigger to promote taurine transport in larvae, especially in muscle tissues, which may be important for larval growth. Results also indicated that the capacity to uptake dietary taurine in the digestive tract is already established in larvae at the onset of metamorphosis. In Senegalese sole juveniles, TauT expression was highest in brain, heart and eye. These are organs where taurine is usually found in high concentrations and is believed to play important biological roles. In the digestive tract of juveniles, TauT was more expressed in stomach and hindgut, indicating that dietary taurine is quickly absorbed when digestion begins and taurine endogenously used for bile salt conjugation may be recycled at the posterior end of the digestive tract. Therefore, these results suggest an enterohepatic recycling pathway for taurine in Senegalese sole, a process that may be important for maintenance of the taurine body levels in flatfish species.

How does fish metamorphosis affect aromatic amino acid metabolism

Aromatic amino acids (AAs, phenylalanine and tyrosine) may be specifically required during fish metamorphosis, since they are the precursors of thyroid hormones which regulate this process. This project attempted to evaluate aromatic AA metabolism during the ontogenesis of fish species with a marked (Senegalese sole; Solea senegalensis) and a less accentuated metamorphosis (gilthead seabream; Sparus aurata). Fish were tube-fed with three l-[U-14C] AA solutions at pre-metamorphic, metamorphic and post-metamorphic stages of development: controlled AA mixture (Mix), phenylalanine (Phe) and tyrosine (Tyr). Results showed a preferential aromatic AA retention during the metamorphosis of Senegalese sole, rather than in gilthead seabream. Senegalese sole’s highly accentuated metamorphosis seems to increase aromatic AA physiological requirements, possibly for thyroid hormone production. Thus, Senegalese sole seems to be especially susceptible to dietary aromatic AA deficiencies during the metamorphosis period, and these findings may be important for physiologists, fish nutritionists and the flatfish aquaculture industry.

Taurine and Fish Development: Insights for the Aquaculture Industry

Expansion of the aquaculture industry is limited by incomplete knowledge on fish larval nutritional requirements. Nevertheless, it is believed that dietary taurine deficiencies may be particularly critical for fish larvae. The reasons include the high taurine levels found during egg and yolk-sac stages of fish, suggesting that taurine may be of pivotal importance for larval development. Moreover, unlike aquaculture feeds, natural preys of fish larvae contain high taurine levels, and dietary taurine supplementation has been shown to increase larval growth in several fish species. This study aimed to further explore the physiological role of taurine during fish development. Firstly, the effect of dietary taurine supplementation was assessed on growth of gilthead sea bream (Sparus aurata) larvae and growth, metamorphosis success and amino acid metabolism of Senegalese sole (Solea senegalensis) larvae. Secondly, the expression of taurine transporter (TauT) was characterised by qPCR in sole larvae and juveniles. Results showed that dietary taurine supplementation did not increase sea bream growth. However, dietary taurine supplementation significantly increased sole larval growth, metamorphosis success and amino acid retention. Metamorphosis was also shown to be an important developmental trigger to promote taurine transport in sole tissues, while evidence for an enterohepatic recycling pathway for taurine was found in sole at least from juvenile stage. Taken together, our studies showed that the dependence of dietary taurine supplementation differs among fish species and that taurine has a vital role during the ontogenetic development of flatfish, an extremely valuable group targeted for aquaculture production.