Impact of environmental and innate factors on the food habit of Chinese perch Siniperca chuatsi (Basilewsky) (Percichthyidae)

Laboratory and field investigations were conducted to study the food habit of Chinese perch Siniperca chuatsi (Basilewsky) from first feeding through adult stage. Only fish larvae were consumed by Chinese perch larvae (2–21 days from hatching), and the presence of zooplankton did not have any significant effect on their survival rate. The ability of Chinese perch to feed on zooplankton is clearly limited by some innate factor. Instead of gill rakers, Chinese perch larvae have well‐developed sharp teeth at the first feeding stage, and are well adapted to the piscivorous feeding habit unique to the larvae of Chinese perch, e.g. they bite and ingest the tails of other fish larvae. At the first feeding stage (2 days from hatching), daily rations were both very low, either in light or complete darkness. Although early‐staged Chinese perch larvae (7–17 days from hatching) could feed in complete darkness, their daily rations were always significantly higher in light than in complete darkness. Late‐staged Chinese perch larvae (21 days from hatching) were able to feed in complete darkness as well as in light, similar to the case of Chinese perch yearlings. Chinese perch yearlings (total length, 14–16 cm) consumed prey fish only and refused shrimp when visual cues were available (in light), but they consumed both prey when visual cues were not available (in complete darkness), suggesting that prey consumption by Chinese perch yearlings is affected by their sensory modality in predation. Both prey were found in the stomachs of similar‐sized Chinese perch (total length, 14–32 cm) from their natural habitat, suggesting that shrimp are consumed by Chinese perch at night. Prey selection of Chinese perch with a length >38 cm, which consumed only fish in the field, appears to be based upon prey size instead of prey type. These results suggest that although environmental factors (e.g. light intensity) affect prey detection by Chinese perch, this fish is anatomically and behaviourally predisposed to prey on live fish from first feeding. This makes it a difficult fish to cultivate using conventional feeds.     

Inhibitory neurotransmitter serotonin and excitatory neurotransmitter dopamine both decrease food intake in Chinese perch (<Emphasis Type="Italic">Siniperca chuatsi</Emphasis>)

Aminergic neurotransmitters play important roles in the regulation of food intake. However, their effects on feeding in fish have been less explored and still unclear. In the present study, the effects of serotonin (5-HT) and dopamine (DA) on food intake were evaluated through intraventricular (ICV) administration in Chinese perch (Siniperca chuatsi) and the mRNA expression levels of neuropeptide Y (NPY), agouti gene-related protein (AgRP), and pro-opiomelanocortin (POMC) were detected. At 1 h post-injection, 5-HT significantly decreased food intake in a dose-dependent manner. The mRNA expression of NPY and AgRP were significantly decreased (p < 0.05), whereas the mRNA expression of POMC was significantly increased (p < 0.05), suggesting the involvement of NPY, AgRP, and POMC in inhibitory action of 5-HT on food intake in Chinese perch. DA significantly decreased (p < 0.05) food intake and AgRP mRNA expression at 1 h post-injection, indicating the inhibitory effect of DA on food intake might be mediated through AgRP. This might shed new light on the regulation of food intake in Chinese perch.     

Role of NPY receptor 8 in regulating of food intake in Chinese perch (Siniperca chuatsi)

Neuropeptide Y receptor Y8 (NPY8R) is a fish-specific receptor, whose role in feeding regulation remains poorly understood. In the present study, two subtypes of NPY8R (NPY8Ra and NPY8Rb) were identified in Chinese perch, and their amino acid sequences were highly conserved in fish. The predicted tertiary protein structures of human NPY1R, Chinese perch NPY8Ra, and NPY8Rb tended to be conserved as a whole. However, the predicted tertiary protein structures of sc-NPY8Ra and sc-NPY8Rb were different at several sites. Chinese perch NPY8Ra and NPY8Rb were mainly expressed in brain. Intracerebroventricular administration of siRNA-NPY8Rb significantly decreased the mRNA expression levels of NPY8Rb and POMC (appetite-suppressive gene) and significantly increased the food intake of Chinese perch at 2 h and 8 h after injection. Similar result has not been observed in the siRNA-NPY8Ra administration group. The above results suggested that NPY8Ra might not play a role in appetite regulation and NPY8Rb might be an effector in the negative feedback regulation of feeding in Chinese perch.

     

斑鳜水库网箱人工繁育与胚胎发育

充分利用水库资源及网箱优势,结合斑鳜繁育生物学特性,在水库网箱上成功批量繁育斑鳜鱼苗,为斑鳜人工繁育开辟一条新途径。2012年5月~2013年7月在辽宁省宽甸县景波水产品养殖场共进行了6批次繁育试验,共计催产亲鱼146组,平均催产率84%,获卵320万粒,平均受精率65%,平均孵化率80%,获水花鱼苗180万尾,利用水库网箱孵化鲤鱼苗配套提供饵料,繁殖了鲤水花11亿尾,共培育斑鳜夏花鱼苗40万尾(平均全长3.1cm),平均2750尾鲤鱼苗培育一尾斑鳜苗,培育前3d斑鳜全长日增长0.54mm,3d后全长日增长约1mm。水温19℃~22℃,显微摄影观察斑鳜胚胎发育时序和特点,受精卵140h7min破膜,胚胎发育划分为6个阶段25时期,提出在斑鳜产卵后配套饵料鱼亲鱼注射催产时间公式:t=t1-t2-t3;(t1:斑鳜胚胎发育时间;t2:饵料鱼胚胎发育时间;t3:饵料鱼亲鱼效应时间)。     

Fat deposition pattern and mechanism in response to dietary lipid levels in grass carp, <Emphasis Type="Italic">Ctenopharyngodon idellus</Emphasis>

This study aimed to evaluate the fat deposition pattern and lipid metabolic strategies of grass carp in response to dietary lipid levels. Five isonitrogenous diets (260 g kg^?1 crude protein) containing five dietary lipid levels (0, 20, 40, 60, 80 g kg^?1) were fed to quadruplicate groups of 15 fish with initial weight 200 g, for 8 weeks. The best growth performance and feed utilization was observed in fish fed with lipid level at 40 g kg^?1. MFI and adipose tissue lipid content increased with increasing dietary lipid level up to 40 g kg^?1, and higher lipid level in diet made no sense. Fish adapted to high lipid intake through integrated regulating mechanisms in several related tissues to maintain lipid homeostasis. In the present study, grass carp firstly increased PPARγ and CPT1 expressions in adipose tissue to elevate adipocyte differentiation and lipolysis to adapt to high lipid intake above 40 g kg^?1. In liver, fish elevated hepatic lipid uptake but depressed biosynthesis of hepatic FAs, resulted in no difference in HSI and liver lipid content among the groups. Only in muscle, fish showed a significant fat deposition when the lipid intake above 40 g kg^?1. The excess lipid, derived from enhanced serum TC and TG contents, was more likely to induce deposition in muscle rather than lipid uptake by adipose tissue in grass carp fed with high dietary lipid, indicating the muscle of grass carp might be the main responding organ to high lipid intake.