EFFECTS OF FEED DIETS ON DIGESTIVE PROTEASES FROM THE HEPATOPANCREAS OF WHITE SHRIMP (Penaeus vannamei)

Protease activities in the hepatopancreas extract (HP) from white shrimp (Penaeus vannamei) fed one of seven test diets for 30 days were evaluated by several methods. The test diet contained 85% of a reference ration for shrimp and 15% of either anchovy meal, tuna waste meal, deboned white fish meal, langostilla meal, soybean meal, and two menhaden meals as a protein replacer. One of the menhaden fish meals tested (B) had the lowest quality as a shrimp feed based on amino acid analysis. SDS-PAGE zymograms of HP from each of the seven diet groups showed similar proteins activity patterns with casein as substrate. The degree of hydrolysis of casein, measured by pH-stat, was also the same for HP from the seven diet groups (P > 0.05). However, total protease activity measured by azocasein hydrolysis (units/g HP) was higher for the diet group fed the test ration containing tuna waste as a replacer (P > 0.05). Trypsin and chymotrypsin activities measured with synthetic substrates (units/mg protein; units/g HP) from animals reared on the diet with menhaden meal B replacer were greater than in the other diet groups (P < 0.05). This study shows that a relatively small amount (15%) of a specific protein replacer in white shrimp rations can influence the protease activity of shrimp HP. Given that digestive proteases such as trypsin can leach into the muscle of postharvest shrimp and thereby cause softening of the meat, the impact of the rearing diet on postharvest shelf-life should be considered along with the standard measures of feed quality that are used by the fish farmer, i.e. animal growth and heatlh.