The influence of algal concentration and body size on filtration and ingestion rates of the clam Tapes decussatus (L.) (Mollusca: Bivalvia)

The filtration and ingestion rates of Tapes decussatus (L.) (12.5-32.5 mm in size), collected from Timsah Lake, Suez Canal, Egypt in 1993, were determined in relation to food concentration and clam dry tissue weight. Suspensions of the unicellular green alga Dunaliella marina, in concentrations ranging from 10³ to 10⁵ cells ml^-1, were provided as food. The filtration rate (F, ml h^-1 clam ^-1) and the weight-specific filtration rate (F“, ml h^-1 mg^-1 dry tissue weight) generally decreased with increased algal concentration following the allometric equations F= 2736.8 W^-0,183 and F’= 12.6 W^-0.182 The amount of water filtered free of particles by a clam of 210 mg dry tissue weight was in the ratio 1:1.4:2.3 with decreasing algal concentrations at 10⁵, 10⁴ and 10³ cells ml^-1, respectively. In contrast, the ingestion rate (I, cells h^-1 clam^-1) and weight-specific ingestion rate (I“, cells h^-1 mg^-1 dry tissue weight), generally increased with increased algal cell concentration following the allometric equations I= 0.01 W^0.87 and I= 0.005 W^0.88, where W is the algal cell concentration per ml. When the clams were fed on 10⁵ cells ml^-1, F and I increased with increased body size following the equations F = 7.5 W^0.74 and I“= 8.89 W^0.63. Otherwise, F“ and I“ decreased with increased body size following the equations F“ 7.5 W^-0.25 and I“ 698.6 W^-0.36, where W is the dry tissue weight in mg.     

Evaluation of microalgae and industrial cheese whey as diets for Tapes decussatus (L.) seed: effects on water quality, growth, survival, condition and filtration rate

As reference diets for bivalve molluscs are missing, this study first evaluated the best mixed algal diet (Tetraselmis suecica Butch/Phaeodactylum tricornutum Bohlin) concentration for 4‐mm‐length Tapes decussatus (L.) clams. It also assessed the performance of an industrial by‐product (cheese whey) as a single diet or supplement for the best algal ration previously determined. Growth, survival, condition index and filtration rate were used to compare the different diets. Implications of rations tested on rearing water quality were also investigated, especially ammonium and heterotrophic bacteria levels. With a food concentration as algal dry weight per total seed live weight of 0.7% day^?1, seed for grow‐out (7 mm) could be obtained within 1 month. A mixture of 25% algal ration and 75% cheese whey gave the best performances. Artificial diets resulted in lower growth rates than live food (20 % to 40% of the best algal ration), but could be considered good maintenance rations in energetic terms. Using cheese whey, and without any algae, hatchery produced seed can be kept economically indoors for at least 30 days without loss in condition.     

Effect of temperature, stocking density and fish size on the ammonia excretion in palmetto bass (Morone saxatilis×M. chrysops)

Three temperature levels (18, 23 and 28 °C), three stocking density levels (0.72, 1.42 and 2.84 kg m⁻³) and two sizes of groups (averaging 104 and 173 g respectively) were used to conduct experiments on the effect of temperature, stocking density and fish size on the ammonia excretion (AE) of palmetto bass ( Morone saxatilis × M. chrysops ). The AE increased with the increase in temperatures by a significant degree ( P <0.05) among different temperature groups. There appeared to be a tendency towards increase of the AE with increased stocking densities, and significant differences ( P <0.05) were found among stocking groups. The AE of smaller size-group was significantly higher than that of the larger size-group. Diurnal variation of AE in palmetto bass showed that the AE rose greatly to reach a peak at about 4 h after feeding, and to the lowest values at about 24 h post feeding in all of the experimental groups.     

Effects of temperature on growth, survival and body composition in larvae of barbel, Barbus barbus (L.)

Barbel larvae were reared for 21 days at 21.0, 24.1, 27.2 or 30.0 °C and fed ad libitum live Artemia nauplii for 16 h a day. The final survival rates exceeded 99 %. The highest mean daily growth rates, amounting to 0.97 mm total length (TL) and 17.3 % body weight (BW), were found at 27.2 °C. The optimum temperature calculated for the growth of larvae was 26.9 °C for TL and 26.5 °C for BW. An increase in water temperature accelerated the development rate to a larger degree than the growth rate. Temperature significantly influenced the final fish body chemical composition. The lowest dry matter content (19.1 %) was found at 24.1 °C. The highest values of ash content were determined for 27.2 and 30.0 °C and were 11.3 and 11.0 % of dry matter, respectively. The fish body caloric value was the highest at 30.0 °C (30.0 J mg^?1). The analysis of changes in the fish body chemical features against the effective day-degrees age scale did not reveal significant influence of temperature. Therefore, the effects of temperature on larval body composition seem to be related mainly to differences in barbel developmental progress at particular temperatures.     

体质量和温度对星洲红鱼耗氧率、排氨率和窒息点的影响

利用实验生态学方法研究了不同温度和体质量对星洲红鱼(Red Tilapia)耗氧率、排氨率和窒息点的影响。结果显示:水温15~35℃时,星洲红鱼的耗氧率、排氨率和窒息点都随着温度的上升而上升,差异显著(P0.05);耗氧率(Ro)、排氨率(RA)与温度(T)的线性回归方程分别为:Ro=0.066 4T+0.008 6(R2=0.969 3)和RA=3.849 4t+3.927 5(R2=0.916 8)。在体重27.50~201.87 g范围内,耗氧率和排氨率随着体重的上升而减小,窒息点随着体重的上升而上升,差异显著(P0.05);耗氧率(Ro)、排氨率(RA)与体质量(W)的线性回归方程分别为:Ro=-0.042 2W+0.312(R2=0.989 6)和RA=-4.281 8 W+26.4(R2=0.988 4)。结果表明,不同温度和体质量对星洲红鱼耗氧率、排氨率和窒息点有明显影响。     

Relationship between growth, food conversion, body size, body composition and temperature in the European eel, Anguilla anguilla L.

Abstract. The influence of temperature on growth of European eels, Anguilla anguilla L., of various body sizes was studied. The mean weight of small eels (SE) (0·6g body weight) maintained at 23°C was significantly lower than that of SE maintained at 25°C or 27°C. No significant differences were found at the end of the experimental period between SE maintained at 25 and 27°C. Similar results were obtained among the moderate-size eels (ME) (l·5gbody weight). However, the average weight increase maintained at 25°C was significantly higher than that of large eels (LE) (3·25g body weight) maintained at 23 or 27°C. It seems that the optimum growth temperature for European eels is different at various stages in their growth and development.     

Influence of feeding frequency on growth and size dispersion in Arctic charr Salvelinus alpinus (L.)

Abstract Dominance hierarchy formation in groups of fish is thought to be a major reason for the development of size heterogeneity. The objective of the current experiment was to examine the influence of different feeding frequencies on growth and changes in size distribution in groups of Arctic charr Salvelinus alpinus (L.). The fish were fed equivalent excess rations continuously for 24 h a day, for 2 h twice a day (early morning and evening), for 2 h once a day in the morning or for 2 h once every other day also in the morning. Growth was measured by individual weighing of fish four times during the 130‐day experiment. Coefficient of variation in size within rearing groups was used to assess size dispersion and the possible development of hierarchies within the groups. Feeding frequency did not influence variation in size within groups, and there were no signs of hierarchy formation.     

Gametogenesis and spawning in the carpet-shell clam, Ruditapes decussatus (L.) (Mollusca: Bivalvia), from the Atlantic coast of Morocco

Abstract. Aspects of gametogenesis of the carpet-shell clam, Ruditapes decussatus (L.), in two lagoons on the Atlantic coast of north Morocco were studied during December 1986 to February 1988. The clams sampled did not show any sign of hermaphroditism and the percentage of males was 42%. The gonads started developing in mid-winter and were ripe in spring. Successive spawnings and reconstitution of gametes look place simultaneously starting from May up to the end of September. Two major spawning periods were noticed: a partial one in May-June and a complete spawning in August-September. From October to December the gonads were at resting stages. In coastal ecosystems where freshwater input is a very important factor, gametogenesis may be affected if clams are exposed to low salinities (less than 15%) for prolonged periods.     

The effect of feeding on oxygen consumption and ammonia excretion of juvenile tench Tinca tinca (L.) reared in a water recirculating system

The effect of feeding frequency (one, three, and continuous feeding), feed ration (0.2, 0.5, 0.8% of total fish biomass), and feeding per se on the oxygen consumption (OC, mg O₂ kg⁻¹ h⁻¹) and ammonia excretion (AE, mg TAN kg⁻¹ h⁻¹) of juvenile tench (body weight 15–19 g) and variations in these parameters in daily cycles were examined. Fish metabolism was studied in a recirculating system (rearing tanks of 0.2 m³, water temperature 23 °C). It was found that oxygen consumption and ammonia excretion depended significantly on feed ration. An increase of feed ration from 0.2 to 0.8% of fish biomass caused an increase of OC and AE from 126.80 mg O₂ kg⁻¹ h⁻¹ and 1.95 mg TAN kg⁻¹ h⁻¹ to 187.35 mg O₂ kg⁻¹ h⁻¹ and 8.80 mg TAN kg⁻¹ h⁻¹ (p<0.05). There was no dependence between feeding frequency and the mean rate of oxygen consumption. However, the relationship between feeding frequency and ammonia excretion by juvenile tench was statistically significant (p<0.05). Feeding frequency significantly affected daily fluctuations of AE and OC. It was found that diurnal variations in metabolic rates were strictly related to tench feeding, and the daily variations of AE were significantly higher than OC.     

Influence of environmental temperature and water oxygen concentration on gas diffusion distance in sea bass (Dicentrarchus labrax, L.)

Gas diffusion distance (GDD) of sea bass was measured in fish bred under farm conditions, at different dissolved oxygen concentrations (DO): normoxia condition (80–100% of the saturation value) and `mild' hyperoxia condition (120–130% of the saturation value). Measures were carried out two times in a year (beginning of summer and autumn) in order to evaluate the effect of water temperature on GDD at the two different dissolved oxygen concentrations. There was a significant influence of both dissolved oxygen concentration (p 0.001) and environmental temperature (p 0.001) on GDD. In summertime it was 1.75 m and 2.31 m for fish reared under normoxia and hyperoxia, respectively, and in autumn 2.51 m and 2.96 m for fish reared under normoxia and hyperoxia, respectively. When DO was reduced at the higher temperatures, GDD decreased as well. Results lead to the conclusion that GDD increased with the increasing of DO, both due to reduced water temperature and to the mild oxygen hypersaturation following application of pure oxygen. The advantage for fish may be found in the compromise between maximising O<sub>2</sub> diffusion at the gills and ions/water intake/loss, known as `osmoregulatory compromise'.     

Size‐related oxygen consumption and ammonia excretion of Eurasian perch (Perca fluviatilis L.) reared in a recirculating system

Oxygen consumption (OC) and ammonia excretion rates (AE) of perch were measured under commercial‐like conditions (temperature 23.3 °C) in both fed (F) and feed‐deprived groups (D). Measurements were taken in triplicate in six sized batches of perch ranging from 44.8 to 336.2 g. The mean daily OC was 288.3–180.6 mg O₂ kg^?1 h^?1 for group F fish ranging in size from 44.8 to 279.4 g body weight. The mean daily AE expressed as total ammonia nitrogen (TAN) was 13.8–5.2 mg TAN kg^?1 h^?1 in the same groups. Daily peaks of OC in group F perch were observed 6 h after the onset of feeding for each size group with relatively stable values up to the end of feeding. Peaks of daily AE in group F perch were observed 10 h after the onset of feeding in each size group, with a rapid decrease up to 16 h after onset. In group D, OC was 181.1–110.5 mg O₂ kg^?1 h^?1 in the weight range 57.9–336.2 g. The daily mean AE was 1.7–0.5 TAN kg^?1 h^?1 in this group. No dramatic peaks of OC and AE were observed in group D perch.     

不同规格及不同盐度下毛蚶稚贝耗氧率和排氨率的研究

研究了毛蚶稚贝不同规格及不同盐度下的呼吸和排氨率。结果表明,耗氧率随着盐度的升高而升高,当盐度达到30后开始下降。排氨率也表现出相似的规律,在盐度27后开始下降。同时,O∶N值也随着盐度的升高而升高,在盐度30后开始下降。而中等规格(2·41±0·20mm)稚贝的耗氧率和排氨率要高于其余两种规格稚贝,使得规格和耗氧率及排氨率并不形成完全的负相关。     

温度对黑鳍棘鲷耗氧率与排氨率的影响

对体重为240.9±27.1 g的黑鳍棘鲷在不同水温(10℃、15℃、20℃、25℃、30℃)条件下的耗氧率和排氨率进行了测试分析。结果表明:黑鳍棘鲷在一定温度范围内的耗氧率和排氨率均随温度的升高而升高,但当水温超过一定值后,其耗氧率和排氨率均随温度的升高而下降。在实验条件下,黑鳍棘鲷的耗氧率与温度的回归方程为Y=-0.489 7X2+27.39X-147.39;排氨率与温度的回归方程为Y=-0.009 3X2+0.508 2X-1.247;耗氧率的最大值为235.61μg/g.h(温度为28.0℃),排氨率的最大值为5.70μg/g.h(温度为27.3℃)。黑鳍棘鲷快速生长期的最适温度为25~28℃。     

温度对黄金鲈(Perca flavescens)耗氧率和排氨率的影响

在不同水温(15、20、25和30℃)下,对体重(46.1±4.5)g黄金鲈(Perca flavescens)的耗氧率和排氨率进行了测定与分析。结果显示:黄金鲈的耗氧率和排氨率均随温度的升高而显著增加(P<0.01);耗氧率和排氨率与温度的关系可用指数方程拟合,其方程分别为:RO=0.0682 e0.0633t,R2=0.9879;RN=2.4593 e0.0904t,R2=0.9703;随着温度的升高氧氮比(O:N)逐渐降低;耗氧Q10值和排氨Q10值均在20~25℃之间最小。结果表明:在各温度水平下黄金鲈基础代谢消耗底物主要均以蛋白质为主,脂肪其次,然而随着温度的升高,黄金鲈利用糖类和脂肪供能的比例逐渐下降,而蛋白质供能的比例逐渐增加。黄金鲈的最适生长温度为20~25℃。     

温度变化对虾夷扇贝耗氧率和排氨率的影响

为探索虾夷扇贝(Datinopecten yessoensis)夏季大量死亡的生理原因,模拟虾夷扇贝筏式养殖区夏季水温变化情况,采用室内控温实验,研究了温度剧烈和缓慢变化对虾夷扇贝耗氧率和排氨率的影响及其影响的差异性。实验设置10℃、15℃、20℃、25℃4个温度梯度,设计温度骤变(每小时升温5℃)和温度缓变(每天升温1℃)2种温度处理方式,测定升温前后耗氧率和排氨率。结果显示,温度变化对虾夷扇贝耗氧率和排氨率影响显著(P0.05)。温度缓变组耗氧率变化范围为1.910～2.722mg(/g·h),排氨率变化范围为1.499～5.003μm/(g·h),耗氧率(OR)和排氨率(NR)与温度(T)之间的相关方程为OR=2.303+0.425T-0.133T(2R2=0.941)和NR=-1.536+4.384T-0.893T(2R2=0.435)。温度骤变组耗氧率和排氨率大于温度缓变组,且温度骤变组耗氧率在15℃、20℃和25℃,排氨率在20℃和25℃与温度缓变组差异显著(P0.05)。     

The effect of food concentration on the scope for growth and growth performance of Ruditapes decussatus (L.) seed reared in an open-flow system

Ruditapes decussatus (L.) seed, 1.6 mm in length, was reared in an open-flow system for 28 days at different concentrations of food: 15, 50, 100, 200 and 300 Isochrysis galbana, clone T-ISO, cells μL^?1. Rates of ingestion, absorption, and respiration were measured during the experiment and used to calculate the energy balance. Rate of ingestion and absorption efficiency were the primary physiological processes governing seed growth. Ingestion rates increased with food concentration, up to a maximum of 100 cells μL^?1. Greater increases in concentration resulted in a decrease in ingestion. Clearance rates were inversely correlated to food concentration. Absorption efficiency, estimated using the Conover method, also decreased with increasing concentrations of food. Respiration rates were independent of food concentration. Potential growth rates were lower than actual growth rates for each of the concentrations tested, although the effect of food concentration on actual and potential growth was equal, with maximum growth occurring at a concentration of 50 cells μL^?1. Thus, SFG (‘scope for growth’) is a good qualitative estimator of actual growth, but a poor quantitative estimator.     

氨氮对黄河鲤肝组织中谷胱甘肽代谢的影响

以黄河鲤幼鱼为研究对象,研究氨氮胁迫对肝组织中谷胱甘肽代谢的影响。研究结果表明:氨氮胁迫诱导黄河鲤幼鱼肝组织中还原型谷胱甘肽(GSH)和氧化型谷胱甘肽(GSSG)含量升高,谷胱甘肽还原酶(GR)活性提高,有效将GSSG还原为GSH,表明谷胱甘肽代谢与黄河鲤对氨氮胁迫的耐受性密切相关。