The production performance of genetically improved farmed tilapia (GIFT, Oreochromis niloticus) and freshwater prawn (Macrobrachium rosenbergii) in periphyton‐based systems were studied in farmers' ponds at Mymensingh, Bangladesh. Fifteen ponds (200–300 m2 area and 1.0–1.5 m in depth) were used to compare five stocking ratios in triplicate: 100% GIFT, 75% GIFT plus 25% prawn, 50% GIFT plus 50% prawn, 25% GIFT plus 75% prawn and 100% prawn. Ponds were stocked at a total density of 20 000 GIFT and/or prawn ha?1. Bamboo poles (mean diameter 6.2 cm and 5.5 pole m?2) were posted in pond bottoms vertically as periphyton substrate. Periphyton biomass in terms of dry matter (DM), ash‐free DM and chlorophyll a were significantly higher in ponds stocked with prawn alone than in ponds with different combinations of GIFT and prawn. Survival of GIFT was significantly lower in ponds stocked with 100% GIFT (monoculture) whereas, that of prawn was significantly higher in its monoculture ponds indicating detrimental effects of GIFT on prawn's survival. Individual weight gains for both species were significantly higher in polyculture than in monoculture. The highest total fish and prawn yield (1623 kg GIFT and 30 kg prawn ha?1) over 125–140 days culture period was recorded in ponds with 75% GIFT and 25% prawn followed by 100% GIFT alone (1549 kg ha?1), 50% GIFT plus 50% prawn (1114 kg GIFT and 68 kg prawn ha?1), 25% GIFT plus 75% prawn (574 kg GIFT and 129 kg prawn ha?1) and 100% prawn alone (157 kg ha?1). This combination also gave the highest economic return. Therefore, a stocking ratio of 75% GIFT plus 25% prawn at a total density of 20 000 ha?1 appeared to be the best stocking ratio in terms of fish production as well as economics for a periphyton‐based polyculture system. 相似文献
A 56-day feeding trial was conducted to access the effect of housefly maggot meal (magmeal) diets on the performance, concentration of plasma glucose, cortisol and blood characteristics of Oreochromis niloticus fingerlings. Seven feeds formulated to contain 36% protein and 20 kJ g−1 gross energy (dry matter basis), were prepared by replacing fish meal with magmeal. Fifteen fingerlings (initial average weight 2.0 ± 0.1 g) stocked per experimental tank were fed in triplicates at 5% body weight in two portions per day (a level previously established). Growth and food conversion ratio were adequate and comparable without any significant differences (p < 0.5) between feeding groups. Mean values for haematocrit and plasma glucose were not significantly different (p < 0.05) among the feeding groups. Fish group fed control diet (containing highest inclusion level of fish meal and without magmeal) gave the lowest haemoglobin concentration (5.96 ± 0.22 g dl−1). This value was significantly different from other feeding groups. Stressful conditions in fish and in mammals are associated with decreased growth, haematocrit (packed cell volume) and haemoglobin values, increased whole blood glucose (hyperglycaemia) and plasma cortisol concentrations. No such physiological changes were observed in this study. Results suggest that feeding O. niloticus fingerling with magmeal diets did not cause any form of physiological stress. Magmeal can be used as a good alternative protein source in tilapia diets. 相似文献