Bibliothek

Notizen: Over a 56-day feeding period, during which juvenile African catfish, Clarias gariepinus (Burchell) increased in body weight at least threefold, diets containing fresh or rancid oils (0.352 and 9.133 mmol MDA equivalents per g oil, respectively) at two levels of supplemental vitamin E (20 or 100 mg all-rac-α-tocopheryl acetate kg-1 dry diet) were fed at 3% body weight per day. On termination of the feeding trial, growth performance and food utilization were assessed. Additionally, health criteria such as hepatosomatic index (HSI), haematocrit, plasma haemoglobin and plasma α-tocopherol concentration were determined. Plasma α-tocopherol was seen to increase significantly (P 〈 0.05) concomitant with dietary dose of the vitamin. Oxidation of dietary lipid source was observed to cause significant depletion (P 〈 0.05) of α-tocopherol from the plasma pool on consumption of the rancid test-diets. Final body weights of the catfish revealed that vitamin E supplementation in rancid diets significantly improved growth (P 〈 0.05), although supplementation into fresh-oil diets did not result in appreciable benefits in terms of final attained weight (P 〉 0.05). Values of other growth parameters and nutrient utilization indices were seen to respond positively to increased vitamin E levels and fresher dietary oils. With respect to other health indices, HSI was strongly correlated (P 〈 0.05) to dietary vitamin E dose and not oil oxidation state, with catfish fed lower α-tocopherol doses exhibiting larger livers proportional to somatic mass. Haematocrit values were significantly (P 〈 0.05) lower in fish fed low-tocopherol/fresh-oil diets. Although no measurably significant differences were found between treatments with respect to plasma-haemoglobin concentration, higher mean values for the fish fed rancid oils at the lower α-tocopherol inclusion level may indicate heightened Spontaneous haemolysis in this group. Mechanisms to account for dietary modulation of health indices in catfish under the present dietary regime are postulated. It was concluded that supplemental α-tocopheryl acetate in diets likely to undergo oxidation, would protect catfish from the nutritional stress imposed by rancid oils and increase growth above levels associated with unsupplemented dietary treatments.