RED DRUM (Sciaenops ocellatus) RESPONSE TO HISTIDINE DEFICIENCY

Due to the increasing inclusion of non-fish based protein sources in fish feeds, several amino acid (AA) deficiencies have presented significant problems to the aquaculture industry.  Historically, restriction of mammalian blood meal, a protein source high in histidine (His), in salmon culture resulted in a high incidence of cataracts.  Higher levels of dietary His are known to ameliorate cataract incidence in salmon culture.  The His requirement of red drum (Sciaenops ocellatus) has been quantified according to weight gain percentage.  However, the effect of His deficiency on the eye, and the lens in particular, of the red drum has not been examined.  Additionally, dietary His has been shown to positively affect erythrocyte fragility in unstressed juvenile grass carp (Ctenopharyngodon idella).

Two diets from a His requirement study were used in this experiment.  A basal diet, known to be below the requirement, was prepared using lyophilized red drum muscle (RDM) as an intact protein (10.5% of dietary protein) supplemented with crystalline AAs (excluding His) to provide a total of 35% crude protein (CP) in the diet, simulating the AA pattern found in RDM. Dietary lipid and dextrin was included to provide, in combination with protein, a total of 13.4 kJ estimated digestible energy/g diet. The basal amount of His provided by RDM when contributing 10.5% of dietary protein was determined to be 0.30 g/100 g diet.  The second diet used consisted of an equal mixture (dry-matter basis) of two diets with His levels known to be above the His requirement of red drum (1.1 and 1.3 g/100 g diet).  These diets were fed to triplicate 38-L aquaria for 8 weeks.  The stocking density was 20 fish/tank with an initial average individual weight of 1.53 g ± 0.08 g.   

At the end of 8 weeks, weight gain of fish fed the His-deficient diet was significantly reduced at only 44% of fish fed the His-supplemented diet. At that time six fish/tank were collected, with the left eye of each fish subjected to histological analysis and the lens of the right eye examined for amino acid composition.  Remaining fish were inspected using slit lamp biomicroscopy for signs of cataracts.  Significant cataracts were observed in 16.7% of eyes examined from fish fed the His-deficient diet while eyes examined from fish fed a sufficient diet did not contain cataracts.  Erythrocyte osmotic fragility was higher in fish fed the His-sufficient diet compared to those fed the His-deficient diet.  Histological analysis is ongoing and will be presented.