Larval Yellow Perch (YP) are characterized by underdeveloped digestive tracts unable to utilize dietary protein efficiently for growth. Hence, development of diets based on proteins of proper molecular weight and optimal amino acid composition are critical to enhancing tissue protein synthesis. Protein hydrolysates have been obtained using in vitro methods and it is evident that enzymatic specificity is crucial to the final protein profile, and therefore, the uptake efficiency of the dietary protein. The objectives of this study were to: 1) Obtain hydrolysate derived from Silver Carp (SC) muscle using adult YP digestive tracts to generate an optimal protein source for YP larvae; and 2) Evaluate the effect of dietary inclusion of the SC hydrolysate on growth, survival, and morphological and molecular responses of the gut.
Briefly, freshly harvested YP stomachs and intestines were ground and used as a direct source of digestive enzymes. Each digestive tract homogenate was added with ground dorsal SC muscle and processed through conditions that mimic stomach digestion (3-4 pH; 2 hours) followed by intestinal digestion (7-9 pH; 4 hours). The final SC hydrolysate was then heated to 90? to halt any further enzyme activity. Omitting the acidic and basic digestion time, the intact SC muscle (control) was obtained using the same procedure.
At 6 dph, ~4,150 larvae were volumetrically stocked into twelve 280L black tanks with a starting water inflow rate of 2 L/min. Clay (10-16 NTU), overhead light (at feeding only), and water surface sprinklers (90o and 45o) were used to deter cannibalism, improve feed intake and swim bladder inflation. The one-month study included 4 dietary treatments in three replicates: SC hydrolysate-based diet (SCH), Intact SC-based diet (ISC, control), and two reference groups: live food (LF; Rotifers/Artemia) and commercial dry diet (CD). The feeding regime included three feeding phases: live food only (7 to 15 dph), dry food transition (16 to 20 dph), and dry food only (20 to 32dph). The experiment finished at 32 dph.
The study found no significant differences in growth performance (final weight/total length); however strong trends were detected. Specifically, the SCH group tended to have higher total length (17.92mm ± 1.02) compared to the ISC (15.57mm ± 1.29) but similar compared to LF (17.68mm ± 1.02) and CD (17.73mm ± 0.68). At 32 dph the cumulative mortality was lowest in SCH (2178 ± 569) and highest in ISC (3668 ± 2026); followed by LF (2888 ± 523), and CD (2345 ± 1168). During the dry feed transition phase, the total mortality of the SCH (454 ± 153) vs. ISC (740 ± 469) likely implies that dietary inclusion of SC hydrolysate improved dry feed intake and mitigated the weaning stress during that phase. Additionally, total mortality of LF (964 ± 63) was over twice that of SCH (450 ± 100) once larvae were weaned. This possibly suggests that larval YP can efficiently utilize dry diets much earlier than previously believed, given the protein fractions are cleaved to species specific profiles. Further results will be shared during the oral presentation.