Effect of winter feeding and starvation on the growth performance of young‐of‐year (YOY) great sturgeon,Huso huso

The objective of this study was to evaluate the feeding rate of the great sturgeon (Huso huso) young of the year (YOY) and to investigate the effects of different feeding rates in maintaining the weight of fish during short periods of winter starvation. Six feeding rates of 0.2, 0.4, 0.6, 0.8, 1.0% body weight (BW) day^?1 and feeding to satiation were considered for the first experiment. Each feeding rate was randomly assigned to three replicate tanks, with continuous feeding throughout a 5‐week winter period of water temperatures below 10°C. Fifteen fish were held in each of 18 tanks with an average initial body weight of 219.6 ± 6.9 g. After 5 weeks of feeding, the best performance was observed in fish fed 1% BW day^?1, but negative growth was observed in fish fed 0.2% BW day^?1. In the second experiment, fish were deprived of feed for 3 weeks at winter temperatures. Weights and condition factors of all fish decreased during starvation, while the differences in mean weight before and after the starvation period were not significant in fish fed a level of 0.2% BW day^?1 and those fish fed to satiation. No mortality was recorded in either experiment. Results of this study indicate that a feeding rate of 1% BW day^?1 would be sufficient for commercial fish farming of YOY of this species to maintain them over winter. Also, to maintain fish weights and prevent weight loss in overwintering ponds, a feeding rate of around 0.3% BW day^?1 seems appropriate for hatcheries.     

Tryptophan requirement of juvenile Asian sea bass Lates calcarifer

The dietary requirement of tryptophan for juvenile Asian sea bass (Lates calcarifer Bloch) was studied. The juveniles (mean initial weight, 5.30 ± 0.06 g) were given semi‐purified test diets containing fish meal, gelatin, squid meal, and crystalline amino acids, for 12 weeks. Each set of isonitrogenous and isocaloric test diets contained graded levels of tryptophan. Fish (15 per tank) were reared in 250‐L fiberglass tanks provided with continuous flow‐through sea water at 26°C and salinity of 28 p.p.t. Fish were fed twice daily at a feeding rate of 8% of the body weight day^?1 for the first 4 weeks and at 3.5–2.5% of the body weight day^?1 from 5 to 12 weeks. The experiment was in a completely randomized design with two replicates per treatment. Mean percentage weight gains and feed efficiency ratios were significantly different in fish fed varying tryptophan levels. Survival was 100% in all treatments. On the basis of break‐point analysis of the growth response, the dietary tryptophan requirement of juvenile Asian sea bass is 0.41% of the dietary protein. This information will be useful in further refinement of practical feed formulations for the Asian sea bass.     

Growth and reproduction of three cladoceran species from a small wetland in the south-eastern U.S.A.

SUMMARY 1. Growth, reproduction and life‐history parameters were measured for three cladoceran species from a small south‐eastern wetland, U.S.A. Simocephalus serrulatus, Diaphanosoma brachyurum and Scapholeberis mucronata juveniles were reared at temperatures between 10 and 25 °C on natural food resources. 2. Growth rate increased with temperature and decreased with individual size for all three species. Maximum somatic growth rate was higher for Simocephalus (49–72% day^?1) and Diaphanosoma (21–91% day^?1) than for Scapholeberis (11–45% day^?1). Multiple regression equations were developed which predict temperature‐ and mass‐specific growth rates for each species. 3. Scapholeberis egg production was positively related to temperature; however, maximum egg production occurred at intermediate temperatures for Simocephalus and Diaphanosoma. Mean cumulative egg production was higher for Scapholeberis (28–92 eggs per female) than for Simocephalus (18–25 eggs per female) and Diaphanosoma (1–41 eggs per female), and was related to differences in reproductive strategy and survival. 4. Survival was inversely related to temperature in most cases. For all three cladocerans, the intrinsic rate of increase (r) and net reproductive rate (R₀) increased with temperature, whereas generation time (G) decreased. Greater egg production by Scapholeberis compared with the other two cladocerans was consistent with higher R₀ values for Scapholeberis at any given temperature. Although r was very similar among species, G was typically longer for Scapholeberis than for Simocephalus and Diaphanosoma. 5. This analysis provides basic information about the population parameters of these coexisting wetland species, and the growth rate models can be applied to field data to determine production dynamics.     

A new energetics model for brown trout, Salmo trutta

1. The chief objective of the present study was to develop a functional model for the daily change in the total energy content of a brown trout, Salmo trutta , (equivalent to growth when positive) in relation to the difference between energy intake (energy content of food) and energy losses (metabolism + losses in faeces and excretory products). Energy budgets for individual fish were obtained in earlier experiments with 210 hatchery trout (live weight = 11–270 g) kept at fairly constant temperatures (mean values ranging from 3.6 to 20.4 °C), but without strict control of temperature or oxygen, and in later experiments, with 252 trout (1–300 g) bred from wild parents and kept at five constant temperatures (5, 10, 13, 15 and 18 °C) and 100% oxygen saturation. Each trout was fed a fixed ration of shrimps, Gammarus pulex, the ration level varying between zero and maximum. 2. Energy intake (C_IN, cal day^??1) was measured directly and expressed as a proportion (p) of the maximum energy intake (C, cal day^??1), the latter being estimated from a model developed earlier. In a new model, energy losses (C_Q, cal day^??1) were expressed as a function of temperature, fish weight and ration level. This model was continuous over the 3.6–20.4 °C range, had twelve fitted parameters and was an excellent fit to the data for the 462 trout (P < 0.001, R² = 0.9970). In an extended model, the weight exponent for energy losses was not assumed equal to that for energy intake, the difference between the two exponents being very small, but significant, with a slight improvement in the fit of the model (R² increased to 0.9972). 3. The limits of model use were discussed. An example of its utility was to elucidate the complex relationships between both positive (growth) and negative daily changes in the total energy content of the trout, and temperature, fish size and variable energy intake. The model has raised several questions for future work, including the effect of increasing energy intake by a change of diet from invertebrates to fish or fish pellets, and a comparison of growth models based on weight or energy changes.     

Lysine and arginine requirements of juvenile Asian sea bass (Lates calcarifer)

Two separate experiments were conducted to determine the dietary requirements of juvenile Asian sea bass Lates calcarifer Bloch for lysine and arginine. Fish (average initial weight: lysine experiment, 13.12 ± 0.12 g; arginine experiment, 2.56 ± 0.13 g) were given amino acid test diets for 12 weeks containing fish meal, zein, squid meal, and crystalline amino acids. Each set of isonitrogenous and isocaloric test diets contained graded levels of L ‐lysine or L ‐arginine. The feeding rate in the lysine experiment was at 4–2.5% of the body weight day^?1, while in the arginine experiment it was at 10–4% of the body weight day^?1. The fish (20 per tank, lysine experiment; 15 per tank, arginine experiment) were reared in 500‐L fibreglass tanks with continuous flowthrough sea water at 27 °C and salinity of 31 ppt in the lysine experiment and at 29 °C and salinity of 29 ppt in the arginine experiment. The experiments were in a completely randomized design with two replicates per treatment. Survival was high in fish given adequate lysine or arginine. Mean percentage weight gains were significantly different in fish fed varying levels of lysine or arginine. Fish fed high levels of L ‐arginine suffered high mortalities. No significant differences were obtained in the feed efficiency ratios (FER, g gain g^?1 feed) of fish fed graded lysine, although the values tended to increase as the dietary lysine level was increased up to the requirement level. In contrast, in the arginine experiment, significant differences in FER of fish among treatments were obtained; the highest FER was observed in fish fed the diet containing an optimum arginine level. On the basis of the growth response, survival, and FER, the lysine and arginine requirements of juvenile Asian sea bass were estimated to be 20.6 g kg^?1 dry diet (4.5% protein) and 18.2 g kg^?1 dry diet (3.8% protein), respectively. These data will be useful in the further refinement of practical diet formulations for the Asian sea bass.     

The effects of water temperature and ration size on growth and body composition of fry of common carp, Cyprinus carpio

Experiment was conducted with the aim of determining the effect of varying water temperature and ration size on growth and body composition of fry of the common carp, Cyprinus carpio. Common carp fry with an initial body weight (BW) of 0.86 g were fed a diet (34.9% protein, 18.3 KJ/g diet) at four ration sizes 4%, 5%, 6% and 7% of their body weight per day and reared at two water temperatures 28 and 32 °C for 60 days. Fry fed with 6% ration showed the highest mean final body weight at 28 °C. Final body weight was significantly (P<0.05) affected by ration and temperature. Cyprinus carpio fry raised at 28 °C had higher feed efficiency (FE) (44.36%) than the fry reared at 32 °C (40.98%) with 4% ration. Further, feed efficiency decreased with increase in ration levels in both temperatures. Protein efficiency ratio (PER) was higher (1.26) at 28 °C than at 32 °C (1.17). At 6% ration, common carp fry showed highest specific growth rate (SGR) (3.82%/day) at 28 °C as compared with at 32 °C (3.57%/day). A linear increase in protein and lipid contents was evident with increasing ration levels up to 6% body weight at both temperatures 28 and 32 °C. Second-order polynomial regression analysis of weight gain and SGR indicated the breakpoints at ration level 6.04% and 6.08% body weight per day at 28 and 32 °C. Hepatosomatic index (HSI) not affected by temperature and ration size while, viscerosomatic index (VSI) influenced (P<0.05) by ration size and temperature. Based on the above results, it may be concluded that 6% BW/day ration is optimal for growth of Cyprinus carpio fry at both the temperatures 28 and 32 °C.     

An energy budget for juvenile thick-lipped mullet, Crenimugil labrosus (Risso)

A series of experiments were carried out to construct an energy budget for juvenile thick lipped mullet, Crenimugil labrosus Risso. A partial factorial experimental design was used to examine the effects of temperature, fish size and meal size on growth. The maximum ration that the fish were able to ingest completely per day was found to be 0·8, 1·4 and 2·3% wet body weight (b.w.) at 13,18 and 23°C, respectively. Ingested maintenance requirements (M.R.) were estimated to be 137, 205 and 288 cal fish^-1 day^-1 at 13, 18 and 23°C, respectively. At 18deg; C, M.R. varied as 25 W^1.04 cal day^-1, where W= fish weight (g). Growth rate increased with increasing temperature. Maximal conversion efficiency was 21–24% and was achieved closer to the maximum ingested ration with increasing temperature. The relationship between respiration rate and W at 18deg; C for 3-20 g fish is described by: respiration rate (ml O₂ h^-1) = 0·128 W^0.976 The energy cost of apparent specific dynamic action at 18deg; C was found to vary between 5·1% and 23·6% of the calorific value of the ingested meal (1% wet b.w.) , mean (± S.E.)=10·2 ± 2·0%. Post mortem analyses of groups of fish fed 0·2, 0·8 and 1·5% wet b.w. meals showed a significant increase in total lipid and a significant decrease in water content with increasing ratio size. A negative correlation was found between body water content and total lipid (and calories). The mean assimilation efficiency (±s.e.) for 5–10 g mullet at 18deg; C was 73·9 ± 3·6%. The observations reported in this study were brought together to construct an energy budget for juvenile C. labrosus which was found to give a reliable prediction (within 10%) of energy demand and growth under the prevailing experimental conditions. Both gross (K₁) and net (K₂) growth efficiencies, based on energy values, increased with increasing ratio size up to satiation and were independent of temperature. The maximum values of K₁ and K₂ observed were 0·33 and 0·46, respectively. The third order efficiency (K₃) appeared to be independent of temperature and ration size; mean values ranged between 0·66 and 0·84.     

Daily energy intake and growth of piscivorous brown trout,Salmo trutta

• 1 The chief objectives were to determine the daily energy intake and growth of piscivorous brown trout (Salmo trutta), and to compare the observed values with those expected from models developed previously for brown trout feeding on freshwater invertebrates. Energy budgets for individual fish were obtained from experiments with 40 trout (initial live weight 250–318 g) bred from wild parents, and kept at five constant temperatures (5, 10, 13, 15, 18 °C) and 100% oxygen saturation. Each trout was fed to satiation on freshly killed sticklebacks (Gasterosteus aculeatus) over a period of 42 days.
• 2 Energy intake (C_IN cal day^‐1) and growth (C_G cal day^‐1) were measured directly and energy losses (C_Q cal day^‐1) were estimated by difference (C_Q = C_IN ‐ C_G). All three variables increased with temperature. A model previously used to predict the daily energy intake (C_IN(INV)) of trout feeding to satiation on invertebrates was adapted, by changing only one parameter, to provide an excellent model (R² = 0.998) for predicting the mean daily energy intake (C_IN(ST)) for the piscivorous trout. Values of C_IN(ST) were 58% (range 48–67%) higher than those for C_IN(INV). A simple model was also developed to estimate mean daily energy losses for piscivorous trout (R² = 0.999). Both models were combined to provide excellent estimates of the daily energy gain (growth) of the piscivorous trout, and this was about three times that for trout feeding on invertebrates. The optimum temperature for maximum growth in energy terms increased from 13.9 °C for trout feeding on invertebrates to 17.0 °C (range 16.6–17.4 °C) for piscivorous trout.
• 3 The models are basically an extension of those developed for trout feeding on invertebrates. They show clearly how energy intake, growth, and the optimum temperature for growth increase markedly when trout change their diet from invertebrates to fish. The implications of this are discussed and it is shown that, in theory, these increases should continue if a more energy‐rich diet was utilised by the trout.

     

Diversity in the influence of temperature on the growth rates of freshwater algae, and its ecological relevance

1. Growth rates of seven species of planktonic algae were determined in culture over a range of temperature from 2 to 35 °C. Additional observations on growth and viability were made for 13 species in the temperature range 20–35 °C. 2. There was a wide range of growth rates between species at their optimal temperatures, from 1.7 divisions day^?1 (Asterionella formosa) to 0.3 divisions day^?1 (Ceratium furcoides). 3. There were considerable differences between species for growth at low and high temperature. Certain algae, including the diatom A. formosa and the flagellates Cryptomonas marssonii, Dinobryon divergens and Eudorina unicocca var. unicocca, had growth rates of 0.4 divisions day^?1 or more at 5 °C. The cyanophyte Tychonema (formerly Oscillatoria) bourrellyi, the xanthophyte Tribonema sp., the desmid Staurastrum cingulum and the large dinoflagellate C. furcoides grew poorly or not at all at this temperature. All 21 species tested could grow at 25 °C, but many – including most of the diatoms, some cyanophytes, and all the flagellates – failed to grow persistently at 30 °C. Only Aphanizomenon flos‐aquae survived with moderate increase at 35 °C, a lethal temperature for the other species. 4. The applicability was considered of proposed quantitative formulations of the rate‐temperature relationship. Simple exponential relationships applied only to very limited lower ranges of temperature. The relationship proposed by B?lehrádek was a better fit over a wider temperature range, but still excluded rate‐decline at high temperature. 5. The interspecific differences found are of potential significance for restrictions in natural distributions associated with season, altitude (especially above 500 m) and latitude.     

Utilization of metabolic scope in relation to feeding and activity by individual and grouped zebrafish, Brachydanio rerio (Hamilton-Buchanan)

Metabolic scope and its utilization in relation to feeding and activity were measured in individual and grouped zebrafish (weight range, 430–551 mg) at 24° C by respirometry. Mean maximum metabolic rate, induced by swimming to exhaustion, R_max(i), was 1223 (s.d. , 157) mg O₂, kg^?1 h^?1 for individuals. Standard metabolic rate, R_s. was 364 mg O₂ kg^?1 h^?1, as estimated by extrapolating to zero activity from measurements of unfed, spontaneously active individuals. Mean routine metabolic rate, R_rout, of individuals was 421 (s.d. , 58) mg O₂, kg_-1 h_-1. The mean voluntary maximum metabolic rate, R_max(v), following transfer of minimally exercised fish to the respirometer, was 1110 (s.d. , 83) mg O₂ kg ^?1 h^?1 for groups of six fish, and was not significantly different from the value measured for individuals, 1066 (s.d. , 122) mg O₂, kg^?1 h^?1. Grouped fish acclimated to the respirometer more slowly than individual fish and exhibited significantly higher R_rout, apparently a result of greater social interaction and activity in groups. Mean R_rout for groups was 560 (s.d. , 78) mg O₂, kg^?1 h^?1. While groups of zebrafish fed a ration of 5% wet body weight day^?1 exhibited consistently higher metabolic rates than fish fed rations of 2.5% wet body weight day^?1 the high ration group still used only a maximum of 77% of the metabolic scope. Zebrafish of the size studied do not appear to demonstrate a high degree of conflict in utilization of metabolic scope by different respiratory components. The metabolic rates measured for zebrafish are among the highest yet measured for fish of similar size and at similar temperatures.     

Effect of ration size and feeding frequency on growth, size distribution and survival of juvenile clownfish, Amphiprion percula

This study describes the growth of juvenile clownfish, Amphiprion percula Lacépède 1802, fed with an artificial diet at six ration sizes of 2, 4, 6, 8, 10 and 12% of body mass per day (BM day^?1) each at a feeding frequency of once, twice and three times per day. The effect of ration size on growth depended on the feeding frequency. In fish fed once a day growth did not improve above a ration size of 8% BM day^?1. At two feedings per day fish required a ration size of at least 6% BM day^?1 to achieve good growth, and fish fed three times per day grew at similar rates above a ration size of 4% BM day^?1. A model to estimate the combined effect of ration size and feeding frequency is presented. The results lead to the suggestion of a simple length‐based feeding regimen that could be tested in future studies on this species or adapted for use in other species.     

Oxygen consumption of burbot, Lota lota(L.), fed different rations of vendace, Coregonus albula L.

The oxygen consumption of adult burbot, Lota lota (L.), was examined to determine the effects of fasting and meal ration on oxygen consumption rates. The temperature (2.1 °C) was selected to represent ambient conditions for burbot in winter. The average pre‐feeding oxygen consumption rate was 29.5 mg kg^?1 h^?1. Feeding affected the oxygen consumption rates since the apparent heat increment correlated significantly with the meal ration. However, the meal ration (i.e. vendace, Coregonus albula L.) did not affect the proportion of the ingested meal energy used in the apparent heat increment. When the meal ration was increased, peak oxygen consumption ranged from 1.2 to 2.2 times higher than the fasting level. Observed low oxygen consumption values suggest that the metabolic processes of burbot are strongly reduced in low temperatures.     

Growth, survival, and starvation resistance of Colorado squawfish larvae

Synopsis Growth and survival of Colorado squawfish, Ptychocheilus lucius, larvae under fluctuating 18, 22, and 26° C (5° C diel fluctuations) and constant 18, 22, 26° C, and 30° C temperature conditions and ration size corresponding to 12.5, 28,64,142, 320 brine shrimp nauplii fish^–1 day^–1 determined from laboratory experiments. Growth was optimal at 31° C and high at temperatures of 26° C to 30° C, at the highest food abundance. Lowest growth was under lowest food rations and highest temperatures. Growth of Colorado squawfish larvae declined substantially at temperatures < 22° C. Neither growth nor survival was significantly different between fluctuating or constant regimes. Survival of Colorado squawfish larvae was highest (95%) at 26.2° C and 235 nauplii fish^–1 day^–1 and high at temperatures of 20 to 30° C with food abundance > 180 nauplii fish^–1 day^–1. Survival was lowest when food abundance was low and temperature was high. Highest mortality occurred more than 20 days after experiments began and mortalities occurred sooner in higher than lower temperatures. Colorado squawfish larvae denied food for 5, 10, or 15 d after first feeding could have begun (6 d), had survival greater than 87 % which was equivalent to continuously fed controls. Survival of fish denied food for 17.5 d after feeding could have begun declined from 84% before feeding to 57% after feeding. Point of no return was estimated between 17.5 and 20 d. Colorado squawfish have relatively high starvation resistance. Low, stable flows that simulate natural hydrographs may enhance growth, survival, and recruitment of early life stages of Colorado squawfish by increasing water temperature and food abundance in regulated rivers of the Colorado River basin.     

Estimation of daily energetic requirements in young scalloped hammerhead sharks, Sphyrna lewini

Juvenile scalloped hammerhead sharks, Sphyrna lewini, are apex predators within their nursery ground in Kāne‘ohe Bay, Ō‘ahu, Hawai‘i. Understanding daily maintenance requirements of a top-level predator is an important step toward understanding its ecological impact within a nursery ecosystem. Juvenile S. lewini were fed a range of daily ration levels to examine the effect of feeding rate on growth and gross conversion efficiency. The von Bertalanffy growth model yielded the best fit to the data, predicting a maintenance ration of 115 kJ kg⁻¹ day⁻¹ (3.4% body weight (BW) day⁻¹) and a maximum growth rate of 38 kJ kg⁻¹ day⁻¹. This finding is in agreement with the previous prediction of high energetic requirements for S. lewini. In combination with the hypothesized food limitation within Kāne‘ohe Bay, this result may explain the observed high mortality rates of S. lewini. Gross conversion efficiency, K ₁, ranged from −36% to 34%, with maximum efficiency at feeding levels of 5.1% BW day⁻¹. The growth conversion efficiency of S.␣lewini is similar to that of lemon sharks and teleost fishes. Growth rates of juvenile S. lewini are possibly restricted by their high metabolic rate, limited food availability and foraging inexperience. By directly examining the effect of ration size on growth and food conversion, it was possible to resolve discrepancies between earlier studies, which used respiratory metabolism and gut content analyses.     

Preliminary results on growth and feeding of wild-caught young goldblotch grouper, Epinephelus costae, in captivity

Growth, food intake, feed conversion, survival, and behaviour of wild‐caught goldblotch grouper, Epinephelus costae Steindachner, (initial weight=103.04 ± 8.27g) were evaluated when reared in captivity. Average weight gains ranged between 0.106 and 0.278 g day^?1, while corresponding gains in length ranged between 0.005 and 0.018 cm day^?1. Average daily growth rate was between 0.075 and 0.232% body weight day^?1 (overall 0.141 ± 0.08% bw/day). Daily rate of feeding was estimated to be between 0.299 and 0.418% bw day^?1 (overall 0.365 ± 0.09% bw day^?1). Food conversion ratio (FCR) ranged between 0.21 and 0.77 (overall FCR=0.423). Food intake was dependent on water temperature.     

Effect of temperature on cell growth and production of transparent exopolymer particles by the diatom Coscinodiscus granii isolated from marine mucilage

In the autumn of 2007, marine mucilage caused by the diatom Coscinodiscus granii occurred in the central area of Ariake Sound, Japan, and resulted in damage to fishery. To elucidate the mechanism underlying the outbreak of marine mucilage, we examined the effect of temperature on cell growth and production of transparent exopolymer particles (TEPs) in a culture of this species. Growth and TEP production of C. granii are influenced by temperature. The maximum growth rate (1.63 divisions day⁻¹) and cell yield (1,280 cells mL⁻¹) at all temperatures were obtained at 30°C. Optimal growth rates (>1.15 divisions day⁻¹: ca. 70% of maximum) and cell yield (>900 cells mL⁻¹: ca. 70% of maximum) were observed at temperatures of 25–30°C. TEP production by C. granii depended on whether volume- or cell-related values were considered. The maximum volume-normalized increase rates and concentrations of TEP at all temperatures were observed at 25°C. However, when production rates and concentrations of TEP were normalized to cell numbers, optimal values were measured at 10–15°C. In Ariake Sound, when marine mucilage caused by C. granii occurred, the temperature ranged from 25.0 to 25.4°C. This suggests that growth conditions of C. granii are important factors for production of marine mucilage.     

Patterns of growth in the early life history of the round herring Etrumeus teres

Early life history traits of young‐of‐the‐year (YOY) round herring Etrumeus teres, caught in Tosa Bay (south‐western Japan), were studied using otolith microstructure analysis for the 2000–2003 year classes. Hatch dates ranged from October to March, and were restricted to either autumn or winter within each year class. YOY ranged from 50 to 123 mm total length (L_T) and from 57 to 192 days in age. The relationship of L_T to otolith radius was linear. Individual growth rates (G_I) were backcalculated between the 70th and 150th days (the size range of most YOY caught) using the biological intercept method. G_I ranged from 0·3 to 1·4 mm day^?1 and decreased in most cases as season progressed irrespective of year class, although G_I in winter cohorts were significantly higher than in autumn cohorts. Otolith growth rates (G_O) ranged from 2·13 to 12·25 μm day^?1 for autumn spawned YOY and from 3·12 to 12·41 μm day^?1 for YOY spawned in winter. The G_O trajectories followed three consistent patterns: (1) an increase in increment widths after first feeding through the second week of larval life, then (2) a plateau in increment spacing before increment widths increased again until reaching the maximum growth rate, followed by (3) a gradual decrease in increment widths until the end of the fifth month. The three stages occurred irrespective of spawning season, although YOY spawned in October and December had higher G_O during stages (1) and (2) than YOY spawned in February and March, whereas higher G_O was observed for late‐winter cohorts in stage (3). Otolith growth from YOY spawned in December and January showed an intermediate pattern between YOY hatched in the early autumn (October to December) and late winter (February to March). The G_O trajectories were cross‐matched to the calendar date to estimate time series of otolith growth rates (G_OTS) for each year. A parabolic trend was found with maximum G_OTS in autumn and spring and minimum values in winter. This trend was significantly correlated to daily sea surface temperature variations. The differences in otolith growth trajectories suggest that the otolith microstructure of E. teres may be used as a natural tag for identifying autumn and winter spawned cohorts.     

Experimental treatments with diflubenzuron and deltamethrin of sea bass, Dicentrarchus labrax L., infected with the isopod, Ceratothoa oestroides

Sea bass with approximate average weights of 5 and 20 g were treated against Ceratothoa oestroides infection with: (i) medicated pellets of diflubenzuron PC90 at a dosage of 3 mg kg^?1 body weight (BW) per day for 14 days. Lice were counted at the beginning of treatment and 19 days after treatment. The drug cleared all lice in the treated group; in the control group, infection remained high 30 days after beginning the experiment. It was concluded that medicated pellets containing 3 mg kg^?1 BW diflubenzuron effectively cleared pre‐adult and adult stages of the isopod parasite over a 14‐day period. No adverse effects were recorded in treated sea bass during the trials and no reinfection occurred 15 days after end of the treatment. (ii) Deltamethrin by means of bath treatments in infected sea bass kept in experimental tanks at 20°C. Before treatment, toxicity on healthy fish was preliminarily assessed by testing five fish from each size group at concentrations of 30, 10, 5, 3, 1, 0.1, 0.05 and 0.01 mg L^?1 for 30 min. The therapeutic concentrations tested were: 10, 5, 3, 0.15, 0.1, and 0.05 μg L^?1 and assessed at 1, 24 and 48 h. Best results were achieved with the 10 μg L^?1 (0.01 mg L^?1) dose, where prevalence was reduced from 100 to 0% over 24 h in both large and small fish. No parasite recovery was observed at 48 h. The dose of 5 μg L^?1 reduced prevalence from 100 to 11.7% and to 0% for small and large fish, respectively. Finally, with the 3 μg L^?1 dose, prevalence was reduced from 100 to 37.5% (small fish) and to 13.3% (large fish). Lower doses were ineffective on the parasites at either 24 or 48 h.     

Number of meals in a day, maximum weight of food consumed in a day and maximum rate of feeding for brown trout, Salmo trutta L.

Brown trout (live weight 9–302 g) were fed to satiation in each of four meals at seven different water temperatures (range 3.8–18.1°C). The period (Ih) from the start of one meal to the start of the following meal was not significantly affected by the weight (Wg) of the trout, but was negatively correlated with water temperature (T°C). A regression equation described the exponential relationship between I and T, and also estimated the number of meals {N) in a day. Values ranged from one meal at about 4°C t o three meals at about 18°C, The greatest increase in appetite occurred at the end of the period I. The maximum weight offood (Drng) eaten in a day was positively correlated with both W and T, a relationship which was well described by a multiple regression equation. The maximum rate of feeding (Fmg h⁻¹) was not significantly affected by W, but increased from 3.8 to 6.8°C, was fairly constant from 6.8 to 19.3°C, and decreased markedly above 19.3°C. Estimates of D and F(with 95% confidence limits) were applicable to a wide variety offood organisms with the exception of mealworms. From comparisons with the results of other workers, it was concluded that the upper limit ofthe daily energy intake determines the optimum temperature for growth.     

Life cycles and growth rates of Baetis spp. (Ephemeroptera: Baetidae) in the laboratory and in two stony streams in Austria

SUMMARY. Larvae of Baetis alpinus, B. lutheri and B. rhodani were reared in a stream channel (water temperature range 4.2–11.4°C) in the laboratory. The larval growth was exponential and the mean specific growth rate varied from 1.93 to 2.24% day^?1 for B. alpinus, 1.49 to 3.41% day^?1 for B. lutheri and 0.79 to 3.11% day^?1 for B. rhodani. These variations in growth rate were related to variations in mean temperature and this was the major factor affecting growth in the laboratory. Non-quantitative samples of the benthos in the Seebach and Unterseebach, two stony streams near Lunz, Austria, were taken at approximately monthly intervals from November 1965 to May 1968. In each year, there were two winter and three summer cohorts for B. alpinus from Seebach and two or three winter and one to three summer cohorts for B. lutheri and B. rhodani from Unterseebach. Over the study period of 30 months, eleven cohorts were recorded for B. alpinus and B. lutheri, and ten cohorts for B. rhodani. The life cycle of a cohort varied from 3 to 8 months in B. alpinus, from 2.5 to 9 months in B. lutheri and from 2.5 to 8 months in B. rhodani. Mean specific growth rate in length varied from 0.82 to 2.97% day^?1 for B. alpinus, 0.96 to 3.33% day^?1 for B. lutheri and 0.65 to 3.01% day^?1 for B. rhodani. The percentage of the variability in growth rate accounted for by variations in mean temperature was 63% for B. alpinus, 91% for B. lutheri and 82% for B. rhodani. Therefore mean temperature was clearly the major factor affecting the growth rates in the field. An agreement was found between the growth rates of B. alpinus in the field and the laboratory. The growth rates of B. lutheri and B. rhodani were slower in the field than in the laboratory at higher temperatures. The possible reasons for this latter discrepancy are discussed, and the growth rates of the three Baetis spp. are compared with those of other species of Ephemeroptera.