Species-specific differences in taurine metabolism highlight conditional essentiality in native South American...

Taurine is considered a conditionally essential nutrient in several teleost fish; however, its metabolic role remains poorly understood in native South American species. In the present study, taurine metabolism was investigated in four aquaculture-relevant freshwater species: Pseudoplatystoma corruscans (spotted catfish), Piaractus mesopotamicus (pacu), Colossoma macropomum (tambaqui), and Arapaima gigas (pirarucu). Individuals were sampled from natural environments during spring and autumn, as well as from commercial aquaculture systems. The condition factor (K), gonadosomatic index (GSI), and hepatosomatic index (HSI) were calculated. Taurine concentrations were quantified in red muscle (RMtau), gonads (Gtau), and stomach contents (Dtau). Additionally, hepatic activities of cystathionine β-synthase (CBS) and cysteine sulphinic acid decarboxylase (CSD) were assessed. Path analysis revealed significant associations between dietary taurine intake, enzyme activity, and tissue taurine deposition. Principal component analysis showed that A. gigas exhibited distinct physiological and metabolic profiles compared to the other species. Taurine concentrations varied according to species, tissue, and origin (wild vs. farmed). Notably, higher taurine levels were detected in wild individuals of P. mesopotamicus and P. corruscans, while farmed C. macropomum and A. gigas exhibited elevated concentrations in specific tissues, such as stomach contents. These findings underscore the species-specific and environmentally modulated nature of taurine metabolism in Neotropical fishes and suggest potential conditional essentiality in A. gigas.