Search

This study investigates the effects of gradual or abrupt changes in rearing salinity on food transit time and digestive enzymes activity of Caspian kutum (Rutilus kutum) larvae. The larvae (532 ± 0.05 mg) were supplied and randomly allocated into 12 tanks at a density of 45 fish per tank. Experimental treatments were fresh water (salinity 0) [FW] as control, exposure to salinity 5 [T1], and gradual transfer to salinity 10 in two steps of first to 5 h, then and after 12 h to a salinity of 10 [T2], and abrupt change (direct transfer to a salinity of 10 [T3]). Results showed at 8 h after start of feeding that the larvae intestine was filled with food pellets except in treatment T1. Enzyme activity responded to salinity change as follows: the highest trypsin, amylase, and chymotrypsin activities were observed in T1; however, these were not significantly different to treatment T3 (P > 0.05). Trypsin activity peaks in the FW and T2 groups occurred 8 h after feeding, and in T3 and T1 groups 5 h after feeding. Peak chymotrypsin and alkaline phosphatase activity was observed 5 and 8 h after feeding in all experiments, respectively. The highest a amylase activity in FW and T2 groups occurred 5 h after feeding, while in T3 and T1 these peaks were observed 8 h after feeding. These results indicate that salinity had some noticeable effects on the activities of digestive enzymes after feeding. [ABSTRACT FROM AUTHOR]

This study attempted to characterize three major classes of digestive enzymes in arowana fish, a popular and highly valuable ornamental fish species using specific substrates and inhibitors in biochemical and SDS-PAGE electrophoresis methods. Acidic pepsin-like enzymes were detected in stomach region at optimum pH of 1.5–2.0 and its importance is shown by a 96.1% inhibition by pepstatin. Trypsin and chymotrypsin were also detected in both pancreas and intestine of this fish. Metalloproteases were shown in electrophoresis studies and further biochemical specific assays confirmed the presence of carboxypeptidases and leucine aminopeptidase. Overall, these alkaline proteases displayed highest activities at pH range of 9.5–10 in both intestine and pancreas with inhibition rate ranging from 30% to 70% by different specific inhibitors. The detection of these enzymes in major digestive organs of this fish reveals a common protein digestion pathway of large polypeptides breakdown by pepsin in stomach, followed by endopeptidase and exopeptidase activities to further degrade chain polypeptides to amino acids for adsorption. While the presence of lipases is expected due to carnivorous nature of this fish, the detection of amylase (0.63–0.73 U) in this study gives indication that there is a possibility for arowana to assimilate a wider range of nutrient as previously though. This means that development of practical dry feed for arowana farming is possible in near future. [Copyright &y& Elsevier]