Haemolymph nitrogenous constituents and nitrogen efflux rates of juvenile shrimp, Penaeus paulensis (Perez-Farfante), exposed to ambient ammonia-N

The effects of increased levels of ambient ammonia-N (7, 20 and 50 mg L^–1) on some blood nitrogenous constituents, and on ammonia-N and urea-N efflux rates of Penaeus paulensis are reported. Haemolymph urea, protein and haemocyanin levels, and the haemocyanin:protein ratio were not significantly altered in any of the situations tested. Sudden exposure to 20 mg L^–1 caused a transient increase in haemolymph ammonia-N levels, and induced pH and uric acid-N levels to increase after 24 h of exposure. A similar transient increase in haemolymph ammonia-N levels occurred during recovery, and the original pH and uric acid-N levels were restored within 30 min. The haemolymph ammonia-N and uric acid-N levels of shrimp held in 50 mg L^–1 for 24 h were higher than those held in low ammonia-N sea water at all times (control). Increased ammonia-N effluxes were found to occur upon recovery, but urea-N effluxes were not different from those of control shrimp. The amounts of ammonia-N which accumulated in the haemolymph of shrimp at high ambient ammonia-N levels were considerably lower than those excreted during the recovery period. Such findings indicate that some of the accumulating haemolymph ammonia-N was transformed into other compounds or stored elsewhere. Possible mechanisms involved are discussed.     

Growth,feed conversion,body composition and nutrient retention efficiencies in fingerling catfish, Heteropneustes fossilis (Bloch), fed different sources of dietary carbohydrate

Growth, conversion efficiency, body composition, nutrient retention and plasma glucose concentration were evaluated in fingerling catfish, Heteropneustes fossilis (Bloch), (3.25 ± 0.1 g) fed iso-nitrogenous (40% crude protein) and iso-caloric (4.7 kcal g^–1 gross energy) test diets containing different sources of carbohydrates (i.e. glucose, fructose, maltose, sucrose, dextrin, pre-cooked corn-starch or α- cellulose) at the 20% level of inclusion. Each dietary treatment had three replicates of 20 fish each. The growth trial was conducted in 70-L high-density polyvinyl flow-through (1–1.5 L min^–1) indoor circular troughs (water volume = 55 L). The catfish were fed to apparent satiation twice daily at 0800 and 1600 h for 6 days a week over ≈ 8 weeks. No significant (P > 0.05) differences were noted in the growth and feed conversion efficiencies when fish were fed the sucrose, dextrin and corn-starch diets. Similarly, growth and conversion efficiencies were similar (P > 0.05) in fish fed the glucose, fructose and maltose diets. The minimum growth and conversion efficiencies were found in fish fed the α-cellulose diet. Post-feeding glucose or maltose resulted in the maximum increase in plasma glucose, followed by sucrose, dextrin, fructose or corn-starch diets, over the 8-h sampling period. Post-feeding α-cellulose produced a relatively low (P > 0.05) variation in the plasma glucose level. Compared to the initial values, higher values of dry matter, crude protein, lipid and body energy, and lower percentages of ash were recorded in catfish fed different sources of carbohydrate. The maximum protein retention rate was seen in fish fed the dextrin diet, while a higher energy retention rate was observed in fish fed the sucrose-based diet. Dietary α-cellulose produced significantly (P < 0.05) lower values of protein and energy retention in fish. The present study indicates that utilization of complex carbohydrates in catfish is more successful with di- and monosaccharides, while dietary α-cellulose is poorly utilized.