No abstract

To evaluate dietary phosphorus requirement of red swamp crayfish (Procambarus clarkia), six diets containing different concentrations phosphorus (2.7, 6.6, 10.5, 14.6, 18.3 and 22.5 g kg−1 diet respectively) were prepared. Each diet was assigned to triplicate of 15 crayfish (initial mean weight: 9.33 ± 0.54 g) for 56 days. The weight gain rate (WGR) significantly increased when dietary phosphorus content increased from 2.7 to 14.6 g kg−1 (p < 0.05), and the feed conversion ratio (FCR) showed an opposite tendency as observed in WGR. As dietary phosphorus level increased, the muscular ash content, the content of calcium and phosphorus in muscle and shell, the inorganic phosphorus concentration in serum, and the protease activities in intestine and hepatopancreas significantly increased (p < 0.05), while the muscular crude lipid content, the lipase activities in intestine and hepatopancreas, the malondialdehyde concentration in hepatopancreas, and the concentrations of total cholesterol, triglyceride and parathyroid hormone in serum significantly decreased (p < 0.05). When crayfish fed diet with phosphorus content from 10.5 to 14.6 g kg−1, the activities of amylase in intestine and hepatopancreas, the activities of catalase in hepatopancreas and the concentration of total antioxidant capacity in hepatopancreas significantly increased (p < 0.05). Broken‐line model analysis in terms of the WGR and FCR indicated that optimal dietary phosphorus requirement of crayfish was from 13.9 to 14.3 g kg−1. The signs of phosphorus deficiency for red swamp crayfish were characterized by poor growth, slightly reduced mineralization and increased body lipid deposition.

Ammonia is a key risk factor in intensive aquaculture systems. This experiment is aimed at investigating the influence of dietary protein levels on genetically improved farmed tilapia (GIFT, Oreochromis niloticus) under chronic ammonia stress. GIFT juveniles of 4.00 ± 0.55  g were exposed to high ammonia level at 0.88 mg/L and fed with six diets comprising graded protein levels at 22.64%, 27.26%, 31.04%, 35.63%, 38.47%, and 42.66% for 8 weeks. The fish in negative control was fed the diet with 31.04% protein in normal water (0.02 mg ammonia/L water). Our results showed that high ammonia exposure (0.88 mg/L) caused significant decrease in fish growth performance, hematological parameters, liver antioxidant enzymes (catalase and glutathione peroxidase), and gill Na+- and K+-dependent adenosine triphosphatase (Na+/K+-ATP) activity. When fish were under high ammonia exposure, the weight gain rate, special growth rate, feed efficiency, and survival rate elevated significantly with dietary protein supplementation increase to 35.63%, whereas protein efficiency ratio, hepatosomatic index, and viscerosomatic index showed a decreased tendency. Dietary protein administration significantly enhanced crude protein but reduced crude lipid contents in the whole fish. Fish fed diets with 35.63%-42.66% protein had higher red blood cell counts and hematocrit percentage than fish fed 22.64% protein diet. The values of serum biochemical indices (lactate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase), hepatic antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase), and gill Na+/K+-ATP activity were all elevated with the increment of dietary protein. Moreover, histological analysis indicated that dietary protein administration could prevent the ammonia-induced damages in fish gill, kidney, and liver tissues. Based on weight gain rate as a response criterion, the optimal dietary protein requirement for GIFT juveniles under chronic ammonia stress was 37.9%.