EFFECTS OF METHIONE AND TAURINE SUPPLEMENTATION ON GROWTH PERFORMANCE, WHOLE-BODY COMPOSITION, AND PLASMA AMINO ACID CONCENTRATIONS OF JUVENILE RED DRUM Sciaenops ocellatus

Methionine (MET) has been demonstrated to be an essential amino acid for fish, and taurine (TAU), a beta sulfonic acid, a conditionally essential nutrient mostly for marine fish species with carnivorous feeding habits. Previous work has shown that red drum or redfish Sciaenops ocellatus requires the supplementation of both MET and TAU, specifically in diets formulated with high inclusion of plant proteins. The minimum dietary requirement for MET was previously established to be 1.06% of dry weight in a 35% crude protein (CP) diet. However, at higher protein levels, there is no published information on the MET requirement of this species. Also, Met is a source of sulfur required in the biosynthesis of TAU. Thus, it was of interest to determine if the requirements for MET and TAU would change at a higher dietary protein level, and if there were nutritional interactions among these compounds.

An 8-week feeding trial was conducted using a factorial design with dietary MET (0.7, 1.2, and 1.7%) and TAU (0.1, 0.45 and 0.9%) levels as the main factors. Diets were formulated with 18% red drum muscle and the remaining protein was provided by plant ingredients. All diets were formulated to contain 40% CP and 13% lipid. Twenty fish with initial average weight of 1.57 grams were stocked into each of 27, 110-L tanks of an indoor brackish water (5-6 ppt) recirculating system. Each diet was fed to three replicate groups of fish twice daily at rates close to apparent satiation. Fish were group weighed weekly to adjust feeding rations.

At the end of the trial, three fish per aquarium were collected for determination of body condition indices and whole-body proximate composition, as well as methionine and taurine concentrations in plasma and tissues.

After the 8-week trial, percentage weight gain (PWG) was affected both by MET and TAU; treatments with 0.45% TAU or higher, and MET at 1.2% or above, had significant higher weight gain (p-value 0.0282, 0.0001, respectively) than the lower TAU and MET treatments. Highest PWG was achieved by fish fed the diet with 1.2% MET and 0.9% TAU, although it was only significantly different from that of fish fed the diet with 1.2% MET and 0.1% TAU, as well as all the 0.7% MET treatments. Feed efficiency (FE) was significantly lower for fish fed the 0.7% MET diets (p-value 0.001). No significant differences were observed for FE with TAU supplementation, although FE was slightly better at the higher inclusion levels. No difference was found among treatments for survival. Muscle ratio was significantly lower (p-value 0.0001) for fish fed the 0.7% MET with 0.1% TAU diet and the 1.7% MET with 0.9% TAU diet compared to the rest of the dietary treatments. Intraperitoneal fat (IPF) ratio and hepatosomatic index (HSI) were affected by MET, with fish fed the diets with 1.7% MET being significantly higher than those fed the 0.7% MET diets (p-value 0.0003 and 0033, respectively). Results of amino acid, whole body, and gene expression are pending further processing.