Showing papers by "Johan A.J. Verreth published in 2000"

Post-prandial protease activity in the digestive tract of African catfish Clarias gariepinus larvae fed decapsulated cysts of Artemia

Abstract: The alkaline proteolytic activity in the gut of African catfish larvae was studied during short time ranges from 30 min to 4 h after ingestion of decapsulated Artemia cysts. The variation in total protease and trypsin activities during the day was monitored during starvation, after one single meal ingestion, and during continuous feeding. In starved larvae the enzymatic activity was low and did not change in time. No significant endogenous secretion of digestive enzymes was detected. The level of alkaline proteolytic activity found in starved larvae was further considered as the basal level. In larvae fed only one meal during the day, the enzyme activity significantly increased from 3 h post-feeding up to a maximum level found 12 h after feeding. In the larvae receiving a meal every 4 h, the effect of feeding on the proteolytic activity was significantly different from the one in fish fed only once a day. The total protease activity in this dietary treatment changed according to the time of feeding and fluctuated around a constant level, which was intermediate between the maximum and the basal level. No rhythmic cycle of enzyme production in the fish was observed when the proteolytic activity was studied during a cycle of 24 h. When specific trypsin activity was measured, a similar pattern was found as with the total protease. The contribution of digestive enzymes from Artemia to the total digestion of food by the catfish larvae was calculated to be less than 1% of the total amount of the proteolytic activity measured in the larval gut.

Metabolic costs of changing the cation–anion difference in the diet of juvenile African catfish Clarias gariepinus (Burchell)

Abstract: The influence of dietary cation-anion difference (CAD, Na K - Cl, mEq kg1) on energy metabolism and nitrogen losses in juvenile African catfish Clarias gariepinus (Burchell) was examined in fish exposed to different dietary CAD levels (-146, 116, 497, 713 and 828 mEq kg1 diet). The experiment was conducted in open circuit balance respiration chambers over a 3-week period. Five 24-h monitoring periods were carried out at 3-day intervals during the experimental period with O2 consumption, ammonia and nitrate nitrite (NOx) and CO2 production being measured at 5-min intervals for each chamber. The negative dietary CAD (-146 mEq kg1) resulted in the highest energy expenditures (83 kJ kg0.8? d1). With increasing dietary CAD levels, heat loss gradually decreased to minimum values of 56 kJ kg0.8 day1 at a dietary CAD level of 713 mEq kg1. Consequently, metabolizable energy utilization efficiency (MEU, percentage of retained energy over metabolizable energy) quadratically (P < 0.05) increased and reached a maximum at a dietary CAD of 713 mEq kg1.