GROWTH AND FEED PERFORMANCE, DIGESTIBILITY AND ACUTE STRESS RESPONSE OF JUVENILE GROUPER (Epinephelus fuscoguttatus) FED DIETS WITH HYDROLYSATE FROM MILKFISH OFFAL

Mamauag, R.E.P.* and Ragaza, J.A.
 
Southeast Asian Fisheries Development Center, Aquaculture Department, Tigbauan, Iloilo, Philippines, 5021.
 

Nutritional qualities of fish processing by-products can further be improved through enzymatic hydrolysis. The objective of the study was to elucidate the efficacy of hydrolyzed milkfish offal at different inclusion levels when fed to juvenile grouper, Epinephelus fuscoguttatus with an initial body weight of 2.88±0.06 g. The animals were fed for 56 days with seven diets supplemented with 0 (control), 5, 15 and 25% of milkfish offal (MO) and milkfish offal hydrolysate (MOH). The diets were formulated to be isonitrogenous (45%) and isolipidic (11%). The diets were assigned to 21 tanks (15 fish tank-1) with each diet having three replicates. Results from the experimental trials indicated that feed conversion efficiency, feed intake and weight gain of fish significantly (P<0.05) improved when fed diets with MOH. No significant differences within the rest of the dietary treatments were observed. Survival rate (> 90%) did not differ in all the dietary treatments. Proximate composition (protein, fat and ash) indicated no significant difference among fish fed from all the dietary treatments. Apparent digestibility of MOH indicated a 95% and 66% digestibility for protein and dry matter, respectively. Plasma stress parameters (cortisol and glucose) were not influenced by the dietary treatment when fish were subjected to an acute stressor (5 minute chasing). Liver morphology indicated normal hepatocyte shape and the presence of lipid droplets in fish fed from all the dietary treatments. The results indicated that milkfish offal processed as hydrolysate can be utilized in fish diets, promote growth and feed efficiency when supplied at 10-15%.