Amino acid composition in eyes from zebrafish (Danio rerio) and sardine (Sardina pilchardus) at the larval stage

A comparative study was performed to identify differences in the amino acid composition of the eyes from zebrafish (Danio rerio) and sardine (Sardina pilchardus) larvae and their link to the environmental adaption of the species. Amino acids in the acidic hydrolysates of eyes from 11 zebrafish and 12 sardine were determined with the use of high-performance liquid chromatography involving precolumn derivatization with ortho-phthalaldehyde. Differences in the content of most amino acids were detected between zebrafish and sardine. These amino acids were aspartate, glutamate, serine, glycine, threonine, arginine, methionine, valine, phenylalanine, isoleucine, leucine and lysine. Of particular note, the percentage of methionine in zebrafish eyes was much higher than that in sardine, whereas the opposite was observed for glutamate and glycine. These results indicate that zebrafish and sardine likely have experienced differences in adaptation to environmental changes. We suggest that the amino acid composition of eyes represents a powerful tool to discriminate between species characterized by different lifestyle and inhabiting different environments.