南方鲇

南方鲇是我国特有的大型肉食性名优鱼类。具有个体大,生长快,抗病力强等特点。其形态特征、生活习性、繁殖与生长、人工养殖等都具有自身的特殊性,也是一种很好的实验研究材料。     

Pattern of energy allocation in the southern catfish (Silurus meridionalis)

Energy budgets were compiled for the southern catfish ( Silurus meridionalis ) under laboratory conditions at different ration size, body weights and temperatures. Though the food energy allocated among the components of the energy budget varied with changing conditions, for the fish fed maximum rations the pattern of energy allocation was independent of body weight and temperature. At the maximum ration about 60% of assimilated energy was deposited in growth and 40% spent in metabolism, indicating a higher proportion allocated to growth and a lower proportion to metabolism than is generally found in fish. This pattern of energy allocation is an energetic strategy adapted to the piscivorous lifestyle of this species.     

The effects of starvation on digestive tract function and structure in juvenile southern catfish (Silurus meridionalis Chen)

The size and functional capacity of the gastrointestinal (GI) tract and associated organs vary in response to environmental cues. The GI tract and associated organs are also very metabolically active in animals. Hence, animals may reduce the size and function of their GI tract to conserve energy when deprived of food. The main aims of this study were to investigate how Silurus meridionalis regulates the function and structure of its GI tract and associated organs during starvation. Starvation induced a decrease in both maintenance metabolism (MO(2rest), decreased by approximately 50%) and respiratory frequency (indicated by double side gill activity and notated as f(R), decreased by 29%). Lipase, trypsin and aminopeptidase-A showed a similar reduction in mass-specific activities during starvation, but pepsin and α-amylase did not. The starvation of experimental fish resulted in a significant reduction in body weight, the wet mass of the liver and the digestive-somatic system, the hepato-somatic index and the condition factor whereas the wet masses of the GI tract, pancreas, gall bladder and the relative intestinal length did not vary significantly during starvation. The reduction in liver wet mass was the main reason for the decrease in the wet mass of digestive-somatic system in this species. Only the mucosal area of the PI was affected significantly by starvation, decreasing by 34% at the end of the experiment. S. meridionalis displayed a decreasing intestinal mucosal area towards the distal intestine, and this gradient was not affected by starvation. The morphology and structure of both the GI tract and the liver were greatly down-regulated, as indicated by decreases in liver cell size, the mucosal thickness of the stomach and intestine, the density of goblet cells and microvilli surface area (MVSA), implying that food deprivation greatly impaired the digestive and absorptive functions of the GI tract in S. meridionalis. When deprived of food, S. meridionalis can endure harsh periods of starvation and adaptively down-regulate the function and structure of the digestive tract with physiological and biochemical strategies.     

Effect of feeding and fasting on excess post-exercise oxygen consumption in juvenile southern catfish (Silurus meridionalis Chen)

The impact of feeding (fed to satiation, 13.85% body mass) on excess post-exercise oxygen consumption (EPOC, chasing for 2.5 min) was investigated in juvenile southern catfish (Silurus meridionalis Chen) (38.62-57.55 g) at 25. Cutlets of freshly killed loach species without viscera, head and tail were used as the test meal, and oxygen consumption (VO(2)) was adjusted to a standard body mass of 1 kg using a mass exponent of 0.75. Resting VO(2) increased significantly above fasting levels (49.89 versus 148.25 mg O(2) h(-)(1)) in 12 h postprandial catfish. VO(2) and ventilation frequency (V(f)) both increased immediately after exhaustive exercise and slowly returned to pre-exercise values in all experimental groups. The times taken for post-exercise VO(2) to return to the pre-exercise value were 20, 25 and 30 min in 12 h, 60 h and 120 h postprandial catfish, respectively. Peak VO(2) levels were 257.36+/-6.06, 219.32+/-6.32 and 200.91+/-5.50 mg O(2) h(-1) in 12 h, 60 h and 120 h postprandial catfish and EPOC values were 13.85+/-4.50, 27.24+/-3.15 and 41.91+/-3.02 mg O(2) in 12 h, 60 h and 120 h postprandial southern catfish, respectively. There were significant differences in both EPOC and peak VO(2) during the post-exercise recovery process among three experimental groups (p<0.05). These results showed that: (1) neither digestive nor exhaustive exercise could elicit maximal VO(2) in southern catfish, (2) both the digestive process and exercise (also the post-exercise recovery process) were curtailed under postprandial exercise, (3) the change of V(f) was smaller than that of VO(2) during the exhaustive exercise recovery process, (4) for a similar increment in VO(2), the change in V(f) was larger during the post-exercise process than during the digestive process.     

Effects of temperature on the specific dynamic action of the southern catfish, Silurus meridionalis.

Specific dynamic action (SDA), the energy expended on all physiological processes that is associated with meal digestion and assimilation, is strongly affected by temperature. We assessed the effects of temperature on the postprandial metabolic response and calculated SDA of the southern catfish, Silurus meridionalis. The fish was fed with experimental diets at a meal size of 4% body mass, and by using an 8-chamber, continuous-flow respirometer the oxygen consumption rate was determined at a 2 h interval until the postprandial oxygen consumption rate returning to the preprandial level, at four different temperatures. The energy expended on SDA (SDA(E)) were 2.71, 3.07, 3.16, and 3.62 kJ, the SDA(coefficients) (energy expended on SDA quantified as a percentage of the digestible energy content of the meal) were 7.70, 9.44, 10.36, and 11.12%, and the peak metabolic rates (R(peak)) of SDA were 3.48, 4.31, 5.96, and 7.30 mg O2 h(-1), at 17.5, 22.5, 27.5, and 32.5 degrees C respectively. The relationships between those parameters and temperature were: SDA(E)=1.74+0.0559T (n=26, r(2)=0.676), SDA(coefficient)=4.10+0.223T (n=26, r(2)=0.726), and R(peak)=-1.34+0.264T (n=26, r(2)=0.896). The SDA durations showed a slow-fast-slow tendency of decrease with increasing temperature, and were 88.00, 85.71, 67.71, and 66.50 h at 17.5, 22.5, 27.5 and 32.5 degrees C respectively. Two separate peaks appeared during the SDA response at 17.5 degrees C, and it might be due to a rapid startup of the mechanical process with a lag of the biochemical process, which suggested that the peaks of "mechanical component" and "biochemical component" of SDA might be separated when temperature was low enough.     

Effect of meal size on postprandial metabolic response in southern catfish (Silurus meridionalis)

Effect of relative meal size (0.6-24%) on specific dynamic action (SDA) was assessed in southern catfish juveniles (48.2+/-3.2 g) at 27.5 degrees C. Cutlets of freshly killed loach species were used as test diet. Energy expended during SDA was linearly correlated with relative meal size (r=0.949, p<0.001, N=47). There was no significant difference in SDA coefficient (energy expended on SDA quantified as a percentage of the energy content of the meal) among different relative meal size groups. Factorial metabolic scope increased from 1.47 to 4.08 when the relative meal size increased from 0.6% to 24%. The peak V O2 increased with meal size, but levelled when relative meal size gradually increased to the maximum. SDA duration showed a S-type (slow-fast-slow) increase course with increased meal size. The results of this study suggest that the high postprandial factorial metabolic scope and a trapezoid SDA curve might be the adaptation strategy of warm water sit-and-wait fish under the natural selection of evolution related to long-term food resources.     

Effects of temperature on the specific dynamic action of the southern catfish, Silurus meridionalis

Specific dynamic action (SDA), the energy expended on all physiological processes that is associated with meal digestion and assimilation, is strongly affected by temperature. We assessed the effects of temperature on the postprandial metabolic response and calculated SDA of the southern catfish, Silurus meridionalis. The fish was fed with experimental diets at a meal size of 4% body mass, and by using an 8-chamber, continuous-flow respirometer the oxygen consumption rate was determined at a 2 h interval until the postprandial oxygen consumption rate returning to the preprandial level, at four different temperatures. The energy expended on SDA (SDA(E)) were 2.71, 3.07, 3.16, and 3.62 kJ, the SDA(coefficients) (energy expended on SDA quantified as a percentage of the digestible energy content of the meal) were 7.70, 9.44, 10.36, and 11.12%, and the peak metabolic rates (R(peak)) of SDA were 3.48, 4.31, 5.96, and 7.30 mg O2 h(-1), at 17.5, 22.5, 27.5, and 32.5 degrees C respectively. The relationships between those parameters and temperature were: SDA(E)=1.74+0.0559T (n=26, r(2)=0.676), SDA(coefficient)=4.10+0.223T (n=26, r(2)=0.726), and R(peak)=-1.34+0.264T (n=26, r(2)=0.896). The SDA durations showed a slow-fast-slow tendency of decrease with increasing temperature, and were 88.00, 85.71, 67.71, and 66.50 h at 17.5, 22.5, 27.5 and 32.5 degrees C respectively. Two separate peaks appeared during the SDA response at 17.5 degrees C, and it might be due to a rapid startup of the mechanical process with a lag of the biochemical process, which suggested that the peaks of "mechanical component" and "biochemical component" of SDA might be separated when temperature was low enough.     

Effects of dietary soybean protein levels on energy budget of the southern catfish, Silurus meridionalis

Energy budgets were calculated for the southern catfish, Silurus meridionalis, fed diets replacing 0%, 13%, 26%, 39%, 52% and 65% fish meal protein with soybean meal (SBM) protein with or without methionine supplementation to apparent satiation at 27.5 degrees C. With increasing dietary soybean protein levels (SPL), the feed energy lost in feces, excretion and metabolism increased, while that available for growth decreased (P<0.05). When 0.12% or 0.26% methionine at 39% SPL was added to reach that in body carcass or the control group (0% SPL), no significant differences were found in each component of energy budgets. When 0.21% or 0.33% methionine at 52% SPL was added to reach the content of methionine in body carcass or the control group, energy spent on growth increased, but that on excretion and metabolism decreased (P<0.05). These results suggested that the differences in growth rate among the southern catfish fed the diets with different SPL were due to decreasing absorption rate, increasing excretion and metabolism with increasing dietary SPL. The most important factor limiting the use of soybean protein was the imbalance of essential amino acids, which resulted in more energy spent on metabolism and excretion, less energy on growth. Supplementation of methionine produced a relatively better amino acid profile and subsequently improved the utilization of soybean protein at high SPL, which resulted in less energy used for metabolism or lost in excretion and more energy available for growth.     

Physiological and morphological responses to the first bout of refeeding in southern catfish (Silurus meridionalis)

Many animals experience fasting because of the high temporal and spatial sporadicity of food availability. Once food is available, animals use external energy to restore their depressed functional performance. In the present study, the physiological and morphological responses to the first bout of refeeding in juvenile southern catfish (Silurus meridionalis) were characterized. Fish that had undergone long-term fasting (fasted for 32 days, the S32 group) exhibited a lower resting metabolic rate ( $ {\dot{\text{M}}} $ O_2rest decreased by 49 %), lower peak metabolic rate ( $ {\dot{\text{M}}} $ O_2peak decreased by 24 %), greater energy expenditure (increased by 15 %) during specific dynamic action (SDA) and longer duration SDA response (increased by 41 %) than those of a control group (S0 group, fasted for 0 days). The S32 group showed a significantly reduced peak gastric evacuation rate (0.131 g meal h^?1) compared with the S0 group (0.315 g meal h^?1). The S0 group also had a shorter gastric evacuation time (36 h) than either of the two fasting groups (both 64 h). The S32 group displayed a higher minimum gastric pH (3.1) than the S0 and S16 groups (2.6). Refeeding did not trigger an increase in the wet mass of the gastrointestinal tract, whereas the liver wet mass of the S0 and the two fasting groups increased significantly with refeeding. The trypsin and lipase of the S0 group showed higher mass-specific activities and organ capacities than either of the two fasting groups at certain specific time points. A similar result was found for aminopeptidase activity. Multiple loach meals equaling 6 % of the body weight of the fed fish completely restored the liver morphology within the S16 but not the S32 group. Our results suggest that the regulation of the digestive performance of the gastrointestinal tract in S. meridionalis that are finishing their first small meal after fasting is delayed compared with that of nonfasting fish and that it is similar to the characteristics (lower $ {\dot{\text{M}}} $ O_2peak, greater SDA and a longer duration of the SDA response) of the refeeding SDA.     

南方鲇两种生长激素受体的结构分析及其组织分布和激素调节

采用生物信息学方法,从东方纯（Fugurubripes）基因组中分离出两种不同基因编码的GHR1（fGHR1）和GHR2（fGHR2）。随后设计引物,采用RT-PCR和Smart^TM Race相结合的方法从南方鲇（Silurus meridionalis）肝脏中克隆出两种不同基因编码的生长激素受体,即GHR1（scGHR1）和GHR2（scGHR2）cD-NA,其全长分别为1985bp（编码602个氨基酸）和2300bp（编码553个氨基酸）。这两种受体都含有生长激素受体典型的标志性基序FGDFS,以及细胞内属于细胞因子受体家族共有的Box1和Box2序列框。同时两者又存在差异,表现在胞外半胱氨酸残基和胞内酪氨酸残基数目的不同。采用半定量RT-PCR方法研究了scGHR1和scGHR2在南方鲇各组织中表达量的差异,结果表明：scGHRl和scGHR2有广泛的组织分布,在肝脏中两者的表达量最高。用17p雌二醇（E2）、17α-甲基睾酮（MT）和可的松（conisol）对南方鲇进行药物处理,结果表明E2能够下调肝脏scGHR1和scGHR2 mRNA水平,而MT上调scGHR1和scGHR2 mRNA水平。同时,经cortisol处理后scGHR1 mRNA表达水平上升,而scGHR2 mRNA表达水平不变。     

A Dermocystidium infection in Trichomycterus sp. (Osteichthyes, Trichomycteridae)

Two whitish elongate cysts in the left pectoral fin of Trichomycterus sp. (Osteichthyes, Trichomycteridae) were packed with Dermocystidium sp. spores. The spores were spherical and had a large PAS positive central refractile body, the cytoplasm being restricted to a narrow peripheral layer containing the nucleus. The cysts were surrounded by a thin homogeneous wall of parasite origin, and there was no encapsulation of the cysts by host tissue.     

南方鲇Vasa基因两种亚型cDNA的克隆及其表达

采用RT-PCR和RACE相结合的方法,从南方鲇分离到Vasa基因的两个亚型scVasa和scVaga-s。它们是同一基因在5′端经选择性剪接的产物,其cDNA全长分别为2525bp和2438bp,编码662和641个氨基酸。两者均具有DEAD-box家族成员特有的8个保守基序和Vasa的典型特征。南方鲇Vasa与银鲫相似性最高（73．3％）。两个亚型均特异地表达于雌雄性腺中。原位杂交结果表明：scVasa主要在卵巢Ⅰ、Ⅱ时相的卵母细胞和精巢的精原细胞和初级精母细胞中表达。半定量PCR结果显示,在生殖周期中,两种亚型在以Ⅱ时相卵母细胞为主体的卵巢恢复期表达均高于以Ⅲ-Ⅳ时相卵母细胞为主体的卵黄生成期[动物学报54（6）：1051—1060,2008]。     

Hypoxia impairs the digestive advantage of individual southern catfish (Silurus meridionalis) with high resting metabolic rates and postprandial metabolic responses

Empirical studies suggest that individuals with a high resting metabolic rate (RMR) are at an advantage under favourable conditions because they digest food rapidly and exhibit a greater growth potential. However, we hypothesised that high-RMR individuals have less energy available for digestion under hypoxia than they do under normoxia due to their relatively high maintenance cost. To test this hypothesis, we measured the RMR and postprandial metabolic responses of juvenile southern catfish, Silurus meridionalis, under normoxia and moderate hypoxia. The results provided the first evidence that (1) both the RMR and postprandial metabolic rate showed repeatability across different water [O₂] conditions and (2) the correlation between the RMR and postprandial metabolic traits differs with changes in environmental factors (water [O₂]). These findings suggested that the digestive advantage of individual southern catfish with a high RMR is impaired under hypoxia.     

延迟首次投喂对南方鲇(Silurus meridionalis Chen)仔鱼身体含能量、体长及游泳能力的影响

在（22.0±0.5）℃条件下,将人工孵化的南方鲇仔鱼分别于出膜后4、5、6、7天进行首次投喂（其中4d的为对照组）,首次投喂前（出膜后4d）取样测量体长、体重、身体含能量作为初始值,于出膜后7d（延迟投喂实验）和21d（继续喂养实验）分别测定体长、体重、身体所含能量和临界游泳速度。结果显示：延迟投喂实验结束时各处理组的体重、身体含能量和体长随首次投喂时间的延迟均呈下降趋势,相对临界游泳速度随首次投喂时间的延迟表现为先提高后降低的趋势,绝对临界游泳速度在延迟投喂2d以内无显著差异;继续喂养实验结束时处理组各指标逐渐接近对照组水平,两种临界游泳速度表现为同步变化趋势;另外,体长特定生长率相对百分比（SGRL%）的变化幅度小于身体含能量特定生长率相对百分比（SGRE%）的变化幅度,而绝对临界游泳速度相对百分比（Ucrit%）的变化又小于体长特定生长率相对百分比的变化。结果表明：早期食物资源的短缺会导致南方鲇仔鱼体重、身体含能量产生明显变化,体长生长速度的变化则相对较小,而短期饥饿不会显著降低南方鲇仔鱼的游泳能力。     

Age and growth of the catfish Bagrus meridionalis Gunther in southern Lake Malawi

Vertebrae from 250 Bagrus meridionalis from the southern end of Lake Malawi were used for age and growth determinations. There is a close correlation between ages determined from length frequency data and ages obtained by back-calculation of the lengths when vertebral rings arc laid down. The rings are laid down annually, probably during the breeding season. Females grow slightly faster than males, the difference being in the order of 1–2 cm/year in the early stages. Recruitment to the trawl fishery takes place in the third year of life. Both sexes breed for the first time at the end of their fourth year. There is a much greater mortality in the male population after 40 cm in length.     

The bioenergetics of the southern catfish (Silurus meridionalis Chen): growth rate as a function of ration level, body weight, and temperature

A feeding-growth experiment was conducted in the laboratory on 114 young southern catfish ( Silurus meridionalis Chen) with initial weights of 8.71–127.9g at 15, 20, 25 and 30°C. The experiment consisted of eight weight-temperature groups, with five ration levels ranging from starvation to satiation in each group. A multiple regression equation fitted to the experimental data was developed to describe the relation between specific growth rate (SGR) and the three factors, ration level (RL), body weight ( W ) and temperature ( T ): SGR = 0.471 + 0.172ln W −0.0443 T +0.0682 T ln(RL + l). This predicts that with increasing temperature the specific growth rate decreases at lower ration levels and increases at higher ration levels. The equation, SGR = a + b ln(RL + l), may be considered as the basic growth model where a is the maintenance metabolism exponent and b is the conversion exponent of the net energy; body weight and temperature influence the two parameters. With this relationship the two antagonistic effects of temperature on growth can be understood, increasing temperature imposes a negative effect on growth due to increment in energy cost for maintenance metabolism, and a positive effect due to higher efficiency of transforming food energy into net energy; the positive effect will increase at higher ration levels. This could also explain why at a restricted ration level relationships between growth and temperature are different in different species.     

Development of microsatellite markers for southern catfish (Silurus meriaionalis) and cross‐species amplification in northern sheatfish (Silurus soldatovi)

Forty microsatellite markers were developed from a (CA)_n enrichment library created from the DNA of southern catfish (Silurus meriaionalis). Also, the population structure of northern sheatfish (Silurus soldatovi) was examined by 24 microsatellite loci. They are polymorphic in at least one of the two geographically distant populations sampled from the Heilongjiang River and the Songhuajiang River in North China, respectively. Unbiased expected heterozygosity levels varied from 0.435 to 0.946 and number of alleles per locus varied from three to 20. Results indicated that these microsatellite loci were highly polymorphic and could be used as genetic markers.