Effect of acute and chronic salinity exposure on the amino acid composition in muscle, intestine and gill tissues of Nile tilapia (Oreochromis niloticus)

Abstract

The present study sought to compare the effect of different salinity stress on amino acid (AA) composition in tissues of Nile tilapia (Oreochromis niloticus). Juveniles of O. niloticus weighing 25.30 ± 4.82 g were exposed to five (5) different salinity concentrations (0, 6, 12, 18, and 24 g/L) for a period of 30 days. Samples of fish tissues (muscles, intestine, and gills) were collected after 3 h (acute) and 30 days (chronic) of salinity exposure for their AA composition analysis. The effect on both acute and chronic salinity exposure on AA composition in the muscles, intestine, and gills of the fish were determined using a Sykam s-433d automatic AA analyzer. Muscle tissue recorded the highest values for both essential AAs (EAAs) and non-essential AAs (NEAAs) with the intestine and gill being second and third, respectively. Both salinity and time (acute and chronic salinity exposures) had significant effects (P < 0.05) on the concentrations of the various AAs measured in the fish muscle. Lysine, Alanine, Aspartic acid, Glutamic acid, Glycine, Serine and Cysteine significantly increased (P < 0.05) in muscle tissue of O. niloticus at high salinity, whereas Arginine, Histidine, Valine, Proline and Tyrosine decreased significantly (P < 0.05) under the same conditions. Comparisons between acute response and chronic response also recorded significant increases (P < 0.05) in concentrations of Arginine, Isoleucine, Lysine, Phenylalanine, Valine, Alanine, Glycine, Proline, and Tyrosine at high salinity concentrations. In the intestine of the fish, salinity did not affect the concentration of AAs. However, both salinity and time altered the tissue AAs compositions of gills as AA concentrations increased significantly (P < 0.05) at high salinities for both acute and chronic responses, except for Methionine, Proline, and Cysteine.