Effects of high temperature on the growth of European whitefish (Coregonus lavaretus L.)

The effect of three different temperatures on growth in a first progeny generation, hatchery reared, subarctic population of European whitefish (Coregonus lavaretus L.) were investigated. The whitefish (start weight 444 g, ±SD 125 g) were reared for 60 days at three constant temperatures; 15, 18 and 21°C and under ambient light regimes for 70°N latitude. The results showed that temperature had a significant influence on the growth of the fish with the highest increase in weight increment occurring at 18°C (mean final weight 656 g ± SD 151 g) compared with the growth of fish held at 15°C (mean final weight 591 g ± SD 143 g) and 21°C (mean final weight 505 g ± SD 121 g). The cumulative per cent mortality of the fish during the experimental period increased with increasing temperature, from 10% at 15°C to 30% at 21°C. The present study indicates that the optimal temperature for farming of European whitefish is somewhere between 15 and 18°C rather than between 18 and 21°C.     

Growth performance of European whitefish [Coregonus lavaretus (L.)] under a constant light and temperature regime

Growth, feed intake and maturation were monitored in a fast‐growing benthivore morph of European whitefish [Coregonus lavaretus (L.)] held under constant light (LD 24:0) and temperature conditions (10°C) for 415 days. Their growth was best described by polynomial regression model and no indication of seasonal patterns (e.g. winter depression) in growth rates was found. There was no significant difference in food conversion ratio (FCR) between periods during the experiment and the FCR was favourable (0.84). Furthermore, there were no differences in growth between males and females. None of the fish became sexually mature by the time the experiment was terminated, although they had reached a mean size of about 444 g. The European whitefish seems to be a promising aquaculture species as the growth rate was relatively high with a remarkable homogenous growth performance between individual fish within each experimental unit, a relatively favourable FCR, a low degree of agonistic behaviour and negligible growth depression due to internal biological rhythms or gonad maturation. These results were obtained at relatively low temperatures that should be beneficial for sustainable cost‐effective farming conditions in cold climate condition in northern Scandinavia.     

Secretion of hatching enzyme and its proteolytic activity in coregoninae (Coregonus albula L andC. lavaretus L) embryos

After the electrial stimulation Coregoninae embryos secreted the hatching enzyme (chorionase) within 0.1–0.5 h, and the dissolution of their chorions lasted 1.2–2.0 h, depending on embryo's developmental stage (DS 13 or DS 14) and water temperature (5.2 or 9.6–9.8°C).Crude chorionase (hatching liquid) ofCoregonus albula andC. lavaretus was collected in large quantities by means of the electric stimulation of eggs. In both species the temperature optimum of proteolytic activity of the crude chorionasc was 30°C; the activity was lost at temperatures < 3-2°C and > 35–40°C. The maximal proteolytic activity was observed at pH 8.5; a rapid decrease in enzyme activity was evident at pH < 7.0, and the activity was zero at pH 6.The temperature-activity curve of chorionase may reflect the adaptation of Coregoninae to hatching immediately after the ice cover recedes from lakes, whereas the rapid decrease of enzyme activity at pH 7 -pH 6 can affect adversely the process of hatching in acidified lakes.     

Individual variability of diel vertical migrations in European vendace (Coregonus albula) explored by stationary vertical hydroacoustics

Abstract –  Diel vertical migration (DVM) is a widespread behavioural pattern in populations of aquatic animals. Its adaptive value is explained by a trade-off between the protection against visually feeding predators in the dark hypolimnion during daytime, and a higher food uptake in the upper food-rich layers during the night. Whereas vertical migration patterns of entire populations have been frequently described, less is known with respect to individual variability of DVM within fish populations. Here, individual migration patterns of European vendace ( Coregonus albula ) are described, obtained by stationary vertical hydroacoustics in Lake Stechlin (Germany) during the dusk and dawn phases of 2 months in 2004. The variability of speeds of depth change was high, with only a few fish rising or falling faster than 1 cm s⁻¹. Swimming activity was not dependent on fish size. There was some evidence that variability of echo strengths was highest in those fish which showed the greatest three-dimensional swimming distances which might indicate a limited swimbladder compensation during vertical migrations. However, migration seems to be performed mainly in a saltatory mode with vertical swimming always interrupted by phases of constant depth. It is suggested that these phases are used for pressure compensation by fish with the consequence that overall the frequency distribution of target strengths deviates only slightly between the start and the end of the recordings. Stationary hydroacoustics proved to be a useful tool for studying individual fish swimming behaviour.     

Diel feeding periodicity in larvae of the vendace (Coregonus albula L.) and influence of food availability and environmental factors on food intake

Abstract— Samples were taken every 2 h for 10 days to determine diel foraging periodicity of vendace larvae in the littoral zone of Lake Lentua, northern Finland and to assess environmental factors affecting food intake. Feeding was associated with daylight conditions, so feeding ceased in the dark. Soft-bodied, rapidly digested rotatorians indicated the periodicity more clearly than hard-shelled prey such as cladocerans and copepodites. Wind events and waves in the littoral zone were the major factors affecting food abundance and feeding by the larvae. Waves induced by strong inshore winds reduced zooplankton density, increasing the occurence of larvae with empty guts to 80%. Reduced food availability was reflected in the guts of larvae within 6 h. The density of suitably-sized zooplankton, together with wind effects and photoperiodism, explained most of the variation in gut content in the larvae.     

An experimental approach to estimating vulnerability of European whitefish (Coregonus lavaretus) ova to predation by invasive ruffe (Gymnocephalus cernuus)

Abstract – The complexity of substrate covering spawning grounds of Coregonus lavaretus is assumed to have a role in the protection of incubating ova from predation. It is believed that the Loch Lomond population of C. lavaretus is adversely affected by invasive ruffe (Gymnocephalus cernuus) predation on eggs. To discover the protective ability of substrate commonly found on whitefish spawning grounds, predation experiments of ruffe on artificial eggs were conducted. These were presented to ruffe over different substrates: sand, gravel, pebbles and cobbles. It was found that the greatest protection was provided by pebbles and gravel. Eggs are exposed on sand, but are protected by small gaps between pebbles and gravel, while in cobbles the gaps between substrate particles are large enough to sometimes allow ruffe to foraging within the substrate. Using these results, a comparison between the potential protective ability of substrates of spawning grounds in four Scottish whitefish sites was attempted.     

Effect of temperature on growth and survival of maraena whitefish Coregonus maraena (Bloch 1779) larvae in controlled conditions

This 28‐day study investigated the effect of three rearing temperatures, 11, 15 and 19°C, on survival and growth of maraena whitefish fry in a recirculating aquaculture system. Three groups of larvae in three repetitions were reared in recirculating system. Each group comprised 200 larvae. Feeding level was fixed at 500–700 Artemia sp. metanauplii per fish per day. Larvae were fed fresh live brine shrimp at 10 ml/tank every 3 hr. Significantly higher body weight (p = 0.00), total length (p = 0.00), larval yield (p = 0.00) and condition factor (p = 0.00) were obtained at 19°C compared to 15 and 11°C, as well as at 15°C compared to 11°C. Significantly higher survival (p = 0.00) was observed in larvae reared at 11 and 15°C compare to 19°C and no significant differences were observed between 11°C compared to 15°C. No significant differences in size heterogeneity among treatments were found (p = 0.46). In larviculture, the optimal assessed temperature for growth of maraena whitefish was 19°C, with highest survival observed at 11°C, at the end of this 28 days trial. The findings in this study apply to the particular study location and may not be applicable more broadly.     

Investigation of wild caught whitefish, Coregonus lavaretus (L.), for infection with viral haemorrhagic septicaemia virus (VHSV) and experimental challenge of whitefish with VHSV

Abstract One hundred and forty-eight wild whitefish, Coregonus lavaretus (L.), were caught by electrofishing and sampled for virological examination in December 1999 and 2000, during migration from the brackish water feeding grounds to the freshwater spawning grounds, where the whitefish may come into contact with farmed rainbow trout. All samples were examined on cell cultures. No viruses were isolated. Three viral haemorrhagic septicaemia virus (VHSV) isolates of different origin were tested in infection trials by immersion and intraperitoneal (IP) injection, using 1.5 g farmed whitefish: an isolate from wild caught marine fish, a farmed rainbow trout isolate with a suspected marine origin and a classical freshwater isolate. The isolates were highly pathogenic by IP injection where 99-100% of the whitefish died. Using an immersion challenge the rainbow trout isolates were moderately pathogenic with approximately 20% mortality, whereas the marine isolate was virtually non-pathogenic. At the end of the experiment it was possible to isolate VHSV from survivors infected with the marine and suspected marine isolates. Because of the low infection rate in wild whitefish in Denmark, the role of whitefish in the spread of VHSV in Denmark is probably not significant. The experimental studies, however, showed that whitefish are potential carriers of VHSV as they suffer only low mortality after infection but continue to carry virus.     

Tagging juvenile European whitefish (Coregonus lavaretus (L.)) with passive integrated transponders—Impact of fish size on growth performance and tag retention

The study examined the effect of PIT tagging and size on the growth, survival, food conversion, tag retention and wound healing in juvenile European whitefish. Three size classes of juvenile whitefish (class S—body weight (b.w.) approx. 4.0 g; class M—b.w. approx. 8.0 g; class L—b.w. approx. 13.6 g) were tagged with PIT implanted intraperitoneally (TROVAN^®, United Kingdom). These groups formed S‐P, M‐P and L‐P respectively. Fish from the control groups (groups S‐C, M‐C and L‐C) were not tagged. Whitefish from the tagged and control groups were reared for 28 days in recirculating aquaculture systems. Only in the fish from the smallest group (group S‐P) was tagging confirmed to have a negative impact on growth rate and survival, which, after 28 days, was 70% in comparison with 94.4% in group S‐C. The rate of wound healing in all whitefish groups was similar. After 28 days following PIT implantation, all wounds were healed. Short‐term PIT retention (28 days) for all the groups was > 90%, and no differences were noted among groups. In summary, it is recommended that whitefish be PIT‐tagged using the intraperitoneal method after they have attained a body weight > 8 g. Tagging smaller specimens of this species leads to higher mortality.     

The large‐scale stocking of young anadromous whitefish (Coregonus lavaretus) and corresponding catches of returning spawners in the River Tornionjoki,northern Baltic Sea

Stocking and fishing effort are two important potentially conflicting factors in fish stock management that require appropriate assessment to ensure a sustainable fishery. In the River Tornionjoki, which discharges into the northern Baltic Sea, a summer‐ascending whitefish, Coregonus lavaretus L., stock has long been a target by traditional dipnet fishing. Enhancement stocking of young whitefish started in the River Tornionjoki in the 1970s after a collapse in catches, with millions of age‐0 whitefish stocked annually in the river, but after about three decades, the stocking rates were considerably reduced. As a result, dipnet catches of whitefish in the Kukkolankoski Rapids rose simultaneously, peaking in the 1980s and 1990s, and then subsequently decreased. There was a significant positive correlation between stocking intensity and catch, both in weight and in numbers, revealing a strong relationship between whitefish releases and dipnet catch. Changes in gillnet fishing effort in the sea affected dipnet catches in weight as well as in mean size of captured whitefish. When the combined effect of stocking and gillnet effort was evaluated, only stocking significantly affected dipnet catches.     

Geosmin depuration from European eel (Anguilla anguilla) is not affected by the water renewal rate of depuration tanks

This study established that geosmin depuration from European eel is not affected by the water renewal rate of depuration tanks. A general fish bioaccumulation model extended with terms that account for effects of tank water renewal rate and system losses of chemicals, predicted strong effects of the water renewal rate of depuration tanks on geosmin depuration from European eel. Model predictions were validated in a depuration experiment with geosmin‐loaded European eel (n = 95) with a mean (SD) individual weight of 134.4 (5.0) g and a mean (SD) lipid content of 33.7 (2.8) % (w/w). Fish were depurated for 24, 48 or 72 h at three different tank water renewal rates (0.3, 3.3 and 33 day^?1). Treatments were installed by three different mean (SD) water flow rates (13.8 (1.3), 143.5 (9.2) and 1511 (80) L kg fish^?1 day^?1) over 30‐L tanks. Eels eliminated geosmin from their bodies, but unlike the model predicted, this was independent of the water renewal rate of the depuration tanks. Although being eliminated from the fish, geosmin hardly appeared and certainly did not accumulate in the water of the depuration tanks as the model predicted. This observation may be explained by geosmin being eliminated from eel as metabolite rather than the parent compound. Geosmin elimination from eel seems not to occur according to the generally accepted passive diffusion mechanism for excretion of lipophilic chemicals, and geosmin biotransformation by the eel seems indicated. Clearly geosmin depuration from European eel cannot be enhanced by increasing water renewal rates of depuration tanks.     

Abiotic and biotic factors affecting recruitment variability of walleye pollock (Theragra chalcogramma) off the Pacific coast of Hokkaido,Japan

Abiotic and biotic factors affecting the recruitment variability of the Japanese Pacific stock (JPS) of walleye pollock (Theragra chalcogramma) were examined using a bivariate regression and multivariate combined model. Of the abiotic variables around Funka Bay (spawning ground), February sea surface temperature (SST) and wind direction index showed significant bivariate relationships with recruitment. February SST was positively related to recruitment, suggesting that warmer water temperature in February favors JPS recruitment. On the other hand, the relationship between February wind direction index and recruitment predicts high JPS recruitment under predominant northwest winds in February. For the biotic variables in the Doto area (nursery ground), significant and negative bivariate relationships with recruitment were observed for catch per unit effort of Kamchatka flounder (Atheresthes evermanni), Pacific cod (Gadus macrocephalus), and walleye pollock, implying an important impact of predation by these groundfishes on JPS recruitment. The overall model incorporating these abiotic and biotic factors successfully reproduced the variability in JPS recruitment. Temperature and wind conditions around the spawning ground along with predator condition in the nursery ground appear to play a dominant role in the recruitment dynamics of JPS. Based on these results and prior knowledge, we propose a new hypothesis to explain the processes controlling JPS recruitment.     

Growth of juvenile common octopus (Octopus vulgaris) in Korean waters is affected by shelter type

This study evaluated the effects of shelter pipes (PS), tube shelters (TS), and no shelter (NS) on the growth of juvenile common octopus (Octopus vulgaris). The grow-out was studied in situ by conducting a passive follow-up survey using integrated transponder tags. The growth and survival rates were evaluated in two experiments. Each experiment included two replicates. Both experiments ran for 60 days, for which each trial included 24 octopuses that were fed once a day a diet of frozen sardines (Sardinops melanostictus) and swimming crabs (Portunus trituberculatus), at 3–8% body weight. We investigated the relationship between the beak microstructure of the common octopus and possible stress events caused by culture conditions at 15 °C for 15 days. The nine juveniles were separated into three groups (NC: natural conditions, PS: culture conditions as a group, and TS: culture conditions with individuals kept separately) to analyze the amount of stress caused by rearing conditions. Stress marks were observed using a high-resolution stereo fluorescence microscope. In Experiment 1, the specific growth rates (SGRs) were 0.20 ± 0.15% per day in the PS group, 0.24 ± 0.10% per day in the TS group, and 0.68 ± 0.48% per day in the NS group. The survival rate was 62.5 ± 6.25%, 37.5 ± 18.75%, and 12.5% in the TS, PS, and NS groups, respectively. The experimental conditions of Experiment 2 were the same as those in Experiment 1, except that Experiment 2 involved different individuals and occurred during a different season. In Experiment 2, the SGRs were 0.54 ± 0.20% per day in the PS group, 0.59 ± 0.22% per day in the TS group, and 0.44 ± 0.10% per day in the NS group. Survival rate was 87.5 ± 6.25%, 75 ± 6.25%, and 75% in the TS, PS, and NS groups, respectively. Regression analysis showed that the water temperature (from 5.4–23.1 °C) affected the growth of octopuses in Experiments 1 and 2. Capture stress was detected in six of the nine individuals (NC, PS, and TS combined). Statistically significant differences in the stress levels were detected between the PS and TS groups (P ≤ 0.1), with the NC group exhibiting no stress lines after initial adaptation, unlike PS. In conclusion, octopuses kept in TS were not affected by stress after initial adaptation.     

Tracking anthropogenic‐ and climatic‐related environmental changes in the remaining habitat lakes of the endangered Atlantic whitefish (Coregonus huntsmani) using palaeolimnological techniques

• 1. Atlantic whitefish (Coregonus huntsmani) is a critically endangered species whose remaining habitat is restricted to three lakes near Bridgewater, Nova Scotia, Canada. Other lakes in this region have been affected by a variety of environmental changes over the past 150 years (e.g. acidic deposition, eutrophication, and climatic changes); however, the extent of the impact on these remaining Atlantic whitefish lakes, and how the current limnological conditions compare with pre‐industrial conditions, is not known.
• 2. Given the lack of long‐term monitoring data, palaeolimnological techniques were used to track environmental changes in these three lakes to infer historic limnological conditions.
• 3. Results of this study show that acidic deposition has had no significant impact on these lakes (diatom‐inferred lakewater pH has changed little over time), nor has the nutrient status of these lakes changed as the sediment profiles have been consistently dominated by oligotrophic diatom taxa.
• 4. Changes in the dominance of diatom assemblages since ～1850, from Aulacoseira distans to Cyclotella stelligera, are correlated with climatic warming (r = 0.48–0.89, P<0.05).
• 5. Contrary to initial concerns, these only remaining habitats of the Atlantic whitefish have not yet been affected by acidic precipitation. However, other potential stressors, such as climatic warming and associated limnological changes, may now be affecting the habitat of this endangered species.

Copyright © 2008 John Wiley & Sons, Ltd.     

Exploring the relative influence of biotic interactions and environmental conditions on the abundance and distribution of exotic brown trout (Salmo trutta) in a high mountain stream

Abstract – In the Logan River, UT, USA, exotic brown trout demonstrate a strong allopatric distribution and occur at high densities at low‐elevation sites and in tributaries, and in low densities at native trout dominated, high‐elevation sites. Summer temperatures and discharge do not appear limiting for growth; adult growth rates were high overall and were greatest when fish were held experimentally at high elevation where they do not occur naturally. Brown trout are superior competitors; competition for space or food was stronger with their own con‐specifics than with other species. Evidence of density dependence was not observed at the juvenile life stage; no consistent relationships were detected between brown trout density and age‐1 condition or lagged, age‐0 weight (g). In contrast, adult brown trout demonstrated density‐dependent effects on condition and growth when reared experimentally. Field estimates of adult growth rates (g·day^?1), although variable, declined subtly with increasing density, and annual survival was significantly greater in the mainstem sites (mean = 52%) relative to a high‐density tributary site (mean = 22%). Annual predicted age‐0 brown trout growth potential was four‐times greater at the lowermost site, compared with the highest elevation site, although fish lost weight over winter months at all sites. While adult density dependence may influence population abundance at some sites, extreme spring–winter conditions may ultimately limit the upper elevational extent of brown trout in this system. With changing climatic conditions and the potential for habitat degradation in the future, these results have important implications for native fish conservation.     

The recruitment of scallops (and beyond) by two different artificial collectors (Gulf of Taranto,Mediterranean Sea)

This study provides for the first time an evaluation of the natural availability of scallop seeds along the coastal area of Taranto (Mediterranean Sea, Southern Italy). To select the best artificial collectors to harvest scallop seeds in this area, cylindrical collectors (Cyl) were compared to traditional ‘Japanese‐style onion bags’ (Bag) across three sites. Scallops represented 26.6% of total bivalve recruitment among all collectors (782 ± 331 ind. m^?2). The most recruited scallops were Flexopecten glaber and Mimachlamys varia. The white (F. glaber) and black scallops (M. varia) were abundant at all three sites, while the queen scallop, Aequipecten opercularis, was only found at one site. Beyond the recruitment of scallops, numerous other potential commercial bivalve species were collected, including Limaria tuberculata, which was the most abundant bivalve species (33.3% of total recruitment). At all sites, Bag collectors had higher recruitment than Cyl collectors. Scallops recruited in artificial collectors exhibited a multicohort size distribution at most sites, suggesting potentially continuous reproductive activity in the scallop populations. F. glaber, M. varia and L. tuberculata could be good candidates to diversify the aquaculture production because of the availability of seed and their growth rate. Moreover, the farming of these bivalves integrates well with other forms of aquaculture (e.g. mussels), thus potentially offering farmers an additional source of income.     

The effects of water temperature and stocking density on survival,feeding and growth of the juveniles of the hybrid yellow catfish from Pelteobagrus fulvidraco (♀) × Pelteobagrus vachelli (♂)

In this study, we aimed to investigate the effects of water temperature and stocking density on the survival, feeding and growth of the juveniles of the hybrid yellow catfish from Pelteobagrus fulvidraco (♀) × Pelteobagrus vachelli (♂) using the parameters as follows: survival rate (%), feeding rate (% day^?1), feed conversion ratio, specific growth rate (% day^?1), coefficient of variation (%), productivity (P, g m^?3 day^?1) and condition factor. We reared the juvenile fish (3.25 ± 0.21 g) at 12 water temperature levels and six stocking density levels (each level included three aquaria in two batches of experiments). The results showed that all groups survived at a temperature range of ≤35°C during a 46‐day experimental period, and they could achieve a high growth at a water temperature range of 26–32°C. The optimal temperature for growth was 29.8°C. Productivity peaked at a stocking density of 1.9 kg m^?3. Our results indicated that the hybrid is very suitable for commercial aquaculture.     

Effects of diet, stocking density and environmental factors on growth, survival and metamorphosis of clam, Paphia malabarica (Chemnitz) larvae

A series of experiments were conducted to evaluate the effects of diet, stocking density and environmental factors on the growth, survival and metamorphosis of short neck clam Paphia malabarica larvae. These experiments examined the following factors: diet [ Isochrysis galbana , Nannochloropsis salina and a mixture of I. galbana and N. salina (1:1 w/w)], stocking density (1, 3, 5 and 7 larvae mL⁻¹), light intensity (unshaded, partially shaded and fully shaded) and water filtration (unfiltered and sand filtered). Results indicated that N. salina could replace 50% of I. galbana as a food source for the clam larvae with an increase in growth, survival (47.2%), metamorphosis (33.5%) and early settlement. Larval growth decreased significantly with increasing stocking density. A density of 1–3 larvae mL⁻¹ appeared to be optimal for normal growth of clam larvae. Neither diet nor stocking density used in the study had a significant effect on larval survival. Under partially shaded (light intensity=1000–5000 lx) and fully shaded (light intensity <1000 lx) conditions, larval growth was significantly faster than under direct sunlight (unshaded). Larvae grew significantly faster in the unfiltered water than in the filtered water.     

环境因子对胶州湾移植底播菲律宾蛤仔滤水率的影响

在实验室条件下对胶州湾移植底播菲律宾蛤仔的滤水率进行了研究。结果表明,不同温度、盐度、pH值条件下的蛤仔滤水率差异显著;2、3龄蛤仔滤水率随环境因子的变化趋势呈极显著正相关。在设定的环境因子梯度下,蛤仔滤水率随着温度、盐度、pH值的升高呈现先增大、后减小的趋势。最大滤水率分别出现在温度23℃、盐度30、pH值8.2。