NUTRITIONAL VALUE OF MODIFIED CARINATA MEAL AS PROTEIN SOURCES FOR HYBRID STRIPED BASS Morone chrysops × Morone saxatilis

Carinata is an oilseed crop undergoing genetic modification to increase the seed oil and erucic acid content for jet fuel production. The solvent extracted seedmeal may be used in animal diets because of its high protein (>40%) content. However, its utilization in fish diets is limited by high crude fiber (>9%), glucosinolates and sinapine. We processed solvent extracted carinata seedmeal by aerobic conversion (ACC) followed by a single wash, or a double wash (WC) without aerobic conversion. Four diets were formulated to contain ~42% protein and 12% lipid, including a fish meal reference diet. All diets contained 10% fish meal and 10% chicken by-product meal. Test diets contained 10 or 30% ACC, or 30% WC.

A 106-day trial was carried out in a recirculating aquaculture system to compare the growth performance of hybrid striped bass (HSB) fed ACC and WC meals. Twenty fish (~19 g each) were stocked in 30 gallon tanks and 6 replicates were used for each treatment. Temperature, pH and dissolved oxygen were monitored daily and averaged 25.6±0.7 ⁰C, 7.5±0.5 and 9.0±1.1 mg/L, respectively. Total ammonia and nitrite were monitored weekly and averaged 0.54±0.28 mg/L and 0.15±0.07 mg/L, respectively. Feed consumption and mortalities were monitored daily and weight gain every three weeks. At the end of the study, three fish per tank were sacrificed, blood was sampled, and then dissected to obtain livers, spleens and visceral fat; all fish were counted and weighed.

Survival (>99%) was similar among treatments. The HSB fed 30% WC had a similar weight gain to HSB fed the reference diet and 30% ACC but better than HSB fed 10% ACC (p=0.010). Relative growth (p=0.015) and specific growth rate (p=0.0016) followed the same trend as weight gain. Fish fed 30% WC and 30% ACC had a similar feed consumption to that of fish fed 10% ACC but better than fish fed the reference diet (p=0.003). The fish fed the reference diet had a similar consumption to those fed 10% ACC diets. The feed conversion ratio of fish fed 30% WC was similar to that of fish fed the reference diet but better than that of fish fed10% and 30% ACC (p=0.001). The protein efficiency ratio of fish fed 30% WC was similar to that of the reference but better than that of 10% ACC and 30% ACC diets (0.001). The ACC diets had a lower protein efficiency ratio than the reference diet. Protein deposition was highest in fish fed the highest carinata meals (p=0.019). Apparent net protein utilization corresponded with feed conversion ratio (0.011). Whole body protein increased with increasing carinata in the diets (0.010). No dietary effect was detected for whole-body ash or moisture contents of the fish. The viscera-somatic, spleen-somatic and visceral fat indices were similar among treatments. However, HSB fed 30% WC had smaller livers and higher condition factors than fish fed other treatment diets. Unconverted carinata increased the Hk content of blood (p=0.011). HSB fed 10 and 30% ACC had similar hemoglobin (Hb, p<0.001) contents that were higher than those of fish fed the reference and 30% WC. There was no dietary treatment effect on lysozyme or ACH₅₀.

Our results show that processed carinata seedmeal is a viable protein ingredient for fish diets. In particular, double washing improved feed conversion and protein efficiency more than aerobic conversion with a single wash. Carinata seeds are high in iron and this may account for the differences observed in Hk and Hb among diets, given that the extra wash step in WC likely reduced iron content.