饲料蛋白质水平与投喂频率对吉富罗非鱼幼鱼生长及部分生理生化指标的影响

为探讨饲料蛋白质水平与投喂频率对罗非鱼生长及生理健康的影响,采用2×3双因子实验,研究饲料蛋白质水平(36.27%和26.02%)与投喂频率(1、2和3次/d)对吉富罗非鱼幼鱼生长、体成分、血清指标和肝胰脏结构的影响。养殖周期为42 d,结果表明:随饲料蛋白质水平的增加,实验鱼的末体质量(FW)、增重率(WGR)、特定生长率(SGR)、饲料效率(FE)、肥满度(CF)、去内脏全鱼灰分(EWA)、内脏水分(VM)、高密度脂蛋白胆固醇(HDLC)水平显著升高(P0.05),而摄食率(FI)、脏体比(VSI)、饲料成本(FC)、去内脏全鱼粗脂肪(EWF)、内脏粗脂肪(VF)、肝胰脏粗脂肪(HF)显著降低(P0.05);随投喂频率的增加,实验鱼的FW、WGR、SGR、肝体比(HSI)、CF、FC、EWF、VF、HF,血清中的总胆固醇水平(TCHO)、HDLC、低密度脂蛋白胆固醇(LDLC)、总蛋白(TP)、甘油三酯(TGK)水平显著升高(P0.05),而FE、蛋白质效率(PER)、去内脏全鱼水分(EWM)、EWA、VM、肝胰脏水分(HM)显著降低(P0.05)。饲料蛋白质水平和投喂频率对实验鱼的FW、WGR、SGR、VM和HDLC的交互作用显著(P0.05)。投喂26.02%蛋白质水平饲料的实验鱼,肝胰脏细胞肿大变形,呈现透明的空泡化,出现细胞核偏移;而投喂36.27%蛋白质饲料的实验鱼,大多数肝细胞胞浆清晰,可观察到的肝细胞空泡面积较小。综合考虑,饲料蛋白质含量为36.27%是适合吉富罗非鱼幼鱼的,其适宜的投喂频率为2次/d以上,可根据罗非鱼市场情况进行调节。

Effects of dietary protein level and feeding frequency on growth and some physiological-biochemical indexes of GIFT strain of juvenile Nile tilapia (Oreochromis niloticus)

Protein is a crucial nutrient in fish diets, and must be supplied in sufficient amounts to assure healthy growth processes and cell renewal. Feeding frequency is important to the survival and growth of fish, especially at early life stages. A few studies reported the relationship between feeding frequency and the dietary protein level, and supported that protein level required for maximum growth may be related to the feeding frequency. But how dietary protein level and feeding frequency affected growth and health of fish was still not clear. Therefore, this study was to estimate the effects of dietary protein and feeding frequency on the growth and health of fish. A 6-week feeding experiment was conducted to determine the effects of dietary protein and feeding frequency on growth, body composition, serum indexes and hepatopancreas structure of the GIFT strain of juvenile Nile tilapia,Oreochromis niloticus. Three replicate buckets of fish average weight of (16.13±0.13) g] were fed to visual satiety with either 36.27% or 26.02% crude protein (CP) dietary, at different feeding frequencies (one meal per day, two meals per day or three meals per day). Each bucket was stocked with 15 fish. At the end of the feeding trial, with increasing dietary protein levels, there was significant increase in the final body weight (FW), weight gain rate (WGR), specific growth rate(SGR), feed efficiency(FE), condition factor(CF), the content of eviscerated whole body crude ash (EWA),  viscera moisture(VM) and the level of serum high density lipoprotein cholesterol (HDLC) of the fish, while there was remarkable decrease in protein efficiency ratio(PER), feed intake(FI),  viscerasomatic index (VSI), feed cost(FC), the content of eviscerated whole body crude fat (EWF), viscera crude fat (VF) and hepatopancreas crude fat (HF)(P < 0.05). As feeding frequency increased, FW, WGR, SGR, hepatosomatic index(HSI), CF, FC, EWF, VF, HF, the level of serum total cholesterol (TCHO), HDLC, low density lipoprotein cholesterol(LDLC), total protein(TP), triglyceride (TGK) increased significantly (P < 0.05), while FE, PER, VM, EWA hepatopancreas moisture (HM) decreased significantly(P < 0.05). Significant interactions between dietary protein level and feeding frequency were found in FW, WGR, SGR, VM and HDLC (P < 0.05). The liver cells of the fish fed with 26.02% protein dietary were swelling, vacuolated and the nucleus offset, but the cells in the fish fed with 36.27% protein dietary had distinct cytoplasm, less vacuolated. Considering all the indexes, the dietary protein content of 36.27% was fit for GIFT strain of juvenile Nile tilapia, Oreochromis niloticus, and the appropriate feeding frequency was more than 2 times/d, which can be adjusted according to the tilapia market situation.