DIETARY HISTIDINE REQUIREMENT OF JUVENILE RED DRUM Sciaenops ocellatus

In order to sustain a growing aquaculture industry, alternative protein sources, as opposed to fishmeal, need to be more effectively utilized. Unfortunately, many alternative protein feedstuffs are limiting in one indispensable amino acids (IAAs). In order to develop nutritious and cost-effective diets, the AA requirements of cultured species must be quantified. Several IAA requirements of red drum Sciaenops ocellatus have already been reported. The red drum's requirement for histidine (His), however, has yet to be quantified. Therefore, the aim of this study was to determine the minimum dietary His requirement of juvenile red drum.

A basal diet 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. Five experimental diets were prepared by supplementing the basal diet (0.3 g His/100 g dry diet) with increasing amounts (0.2 g/100 g dry diet) of His (0.5, 0.7, 0.9, 1.1, 1.3 g/100 g dry diet). This range of dietary His levels was chosen based on His requirements previously established for other species. The experimental diets were kept isonitrogenous by adjusting the inclusion of an aspartate/glutamate premix. Red drum juveniles (0.98  0.08 g) were stocked in 38-L aquaria at a density of 20 fish/tank. Dietary treatments were randomly assigned to triplicate aquaria and fish were fed to apparent satiation, twice daily.

Based on weekly weight gain percentage, preliminary results (week 4) from this trial suggest the dietary histidine requirement of juvenile red drum to be near 0.9 g/100 g dry diet (Figure 1). According to a preliminary ANOVA, fish fed diets with His at 0.9, 1.1, 1.3 g/100 g dry diet have grown significantly more than fish fed the basal diet (p0.05). However, this feeding trial is ongoing and will last a total of 6 weeks, at the end of which we expect to find a clear effect of the different dietary His levels on weight gain of juvenile red drum, allowing us to precisely quantify the minimum dietary His requirement.