Digestive enzymes activity of wild and cultivated grey mullet Mugil cephalus

Abstract

Digestive tract indices and digestive enzyme distribution in digestive organs of wild and cultivated grey mullet Mugil cephalus were studied,and effects of different temperature and pH on digestive enzyme activities were investigated in both populations.The results showed that in wild and cultivated grey mullets,the ratio of intestine gut length to body length were 2.886±0.301 and 3.315±0.141 while the ratios of viscera,liver and stom-ach weight to body weight were 0.043±0.001 and 0.048±0.004,0.009±0.001 and 0.007±0.000,0.008±0.002 and 0.007±0.000,respectively.The activities of protease in different organs were sequenced as follow: hind-gutforegutmidgutstomachhepatopancreas in wild grey mullets and foregutmidguthindgut hepato-pan-creasstomach in cultured ones,while the activities of amylase were in the order of hindgut pyloric caecummidgutforeguthepatopancreasstomach in wild grey mullets and pyloric caecum foregutmidgut hindgutstomach hepatopancreas in cultured ones.The differences of amylase activity in every part between the populations were extremely significant(P0.01).No significant differences of protease activity in hepatopancreas and stomach exited between the two populations(P0.05),but in midgut the difference was significant(P0.05),and in foregut and hindgut,the difference were extremely significant(P0.01).For the amylase in wild grey mullet,the optimum temperatures were 40℃,45℃,45℃,45℃,40℃,45℃ in hepatopancreas,stomach,foregut,midgut,hindgut and pyloric caecum,respectively and the optimum pH in hepatopancreas was 6.2 and in other tissues was 7.2.For amylase in cultured grey mullet,the optimum temperatures were 40℃,40℃,40℃,45℃,40℃,40℃ in hepatopancreas,stomach,foregut,midgut,hindgut and pyloric caecum,respectively and the optimum pH in stomatch and foregut were 2.2 and 8.0,and in other tissues was 7.2.For protease in wild grey mullet,the optimum temperature in hepatopancreas,stomach,foregut and hindgut was 45℃,while in midgut was 50℃ and the opti-mum pH of protease in stomach was 3.2,and in other tissues was 7.2.For protease in cultured grey mullets,the optimum temperature in hepatopancreas,stomach and midgut was 40℃,while in foregut and hindgut was 45℃ and the optimum pH of protease in stomach was 3.2,and in other tissues was 7.2.This study shows that in aqua-culture we should consider not only the assimilation of protein,but also that of saccharide.Adjustment of the amount and proportion of amylase and protein according to environmental conditions could promote production and save cost.