Experimental estimation of the food intake of larval vendace (Coregonus albula L.) under field conditions

We estimated the food intake of larval vendace (Coregonus albula L.) directly in an experimental chamber under field conditions. The larvae were stocked into net enclosures and reared without additional feeding for 6 weeks immediately after the ice melted in Lake Ylä-Enonvesi, Eastern Finland. The food intake was estimated on the basis of the decrease in zooplankters due to larval predation in the transparent plastic chambers anchored in the littoral zone. The experiments were carried out twice in 1988 and three times in 1989 (May–June). The numbers of zooplankters inside the chambers were counted from the subsamples using an inverted microscope. The relative daily ingestion rate (mg dry mass of prey animals mg dry mass of fish ^–1 24 h^–1) of the larvae of different sizes was: 1.09 and 0.84 for 9–11 mm larvae, 1.27 for 11–13 mm larvae and 0.34 for 17–20 mm larvae. The measured ingestion rate is presumed to be near the maximum consumption of the larvae. This method could provide accurate estimates of food consumption in the field or in the laboratory.     

Egg quality and female condition in vendace (Coregonus albula L.) before and during spawning

The fat content of muscle, liver and eggs of vendace (Coregonus albula L.) were measured during the maturation of ovaries in summer. The fat content of eggs was at its highest in July and that of muscle in August during the optimal feeding season. Significant differences were not found in fat content between lakes Suvasvesi and Southern-Kallavesi in central Finland. There were no essential differences in fatty acid composition between muscle, liver and eggs of Lake Suvasvesi vendace. During the last month before spawning in October the gross energy and fat contents of eggs decreased in Lake Suvasvesi vendace. The fat and vitamin C contents of muscle as well as the liver index of females decreased during this time also. In males the corresponding decrease did not occur, indicating that spawning is a greater stress for females than for males. The egg quality and condition of Lake Inarijärvi vendace were about the same as those of Lake Suvasvesi vendace. The unfavourable conditions of Lake Inarijärvi, located in northern Finland, are reflected in the size of ovaries, which is known to be smaller (gonadosomatic index < 20%) than in Lake Suvasvesi (GSI 26–27%). Vendace, then, maintain the quality of eggs at the expense of their number.     

Temperature requirements for growth and survival of larval vendace, Coregonus albula (L.)

Water temperatures from 15.0 to 20.0° C are recommended as the most suitable for sustained production of larval vendace, as indicated by the developmental rates, the instantaneous rates of growth, mortality, and the net biomass gain of larvae reared at eight constant temperatures from 4.8 to 22.1° C. The recommended temperatures are optimal when the available food and photoperiod are not the limiting factors. Temperatures higher than 22.0° C will cause increased mortality, whereas temperatures lower than 15.0° C, although advisable when food is limited, will retard larval growth and development.     

Effect of bleached kraft pulp mill effluent on hepatic biotransformation reactions in vendace (Coregonus albula L.)

1. The effect of bleached kraft pulp mill effluent (BKME) on xenobiotic biotransformation enzyme activities in the liver of vendace (Coregonus albula L.) was studied by exposing some fish in field laboratory tanks at 0, 0.1, 0.2 and 0.5% (v/v) effluent concentrations of BKME corresponding to 0-0.08 toxic units and others in clean water as controls. 2. Slight increase (57%, 68%) in polysubstrate monooxygenase enzyme activities, measured as benzo(a)pyrene hydroxylase and 7-ethoxycoumarin O-deethylase activities, was observed in a dose related manner after 70 days of exposure to 0.5% concentration of BKME. 3. Highest increase was observed at 0.2% effluent concentration after 120 days of exposure, measured as benzo(a)pyrene hydroxylase activity. 4. BKME had an affect on UDPglucuronosyltransferase, at the beginning (14-70 days) by decreasing and in longer exposure (120 days) by slightly increasing the activity.     

Vertical distribution of vendace Coregonus albula L. and other pelagic fish species in some Polish lakes

Studies on the vertical distribution of vendace Coregonus albula (L.), smelt Osmerus eper-tanus (L.) and bleak Alburnus alburnus (L.) in lakes have been carried out with the application of an echo sounder and then compared with control catches of fish and plankton, Methods and results have been discussed. Some remarks have been made on taking these species of fish.     

Genetic changes in a vendace Covegonus albula (L.) population, 92 years after introduction

The Osensjmn vendace, Coregonus albula (L.), population was founded in 1895 by introduction of about 90 000 fry from Lake Mjøsa. After 92 years, or about 46 generations of isolation, remarkable genetic changes were evident among the transplants compared to their source population. Electrophoresis of 33 enzyme loci revealed that allele frequencies differed significantly in eight of the 10 polymorphic loci. Nei's unbiased genetic distance was D = 0.012, representing the level of population differentiation usually observed among distant watercourses in vendace. Genetic variability was clearly higher among the transplants: average observed heterozygosity was 14.8% compared with 11.2% among Lake Mjøsa vendace. The high genetic variation among Osensjoen vendace shows that the divergence is not due to a small number of founders or bottlenecks in later generations. Selection by the contrasting environmental conditions between the habitats of the donor and transplanted populations is the most plausible hypothesis to explain the genetic changes in the Osensjsen vendace.     

Survival, growth and feeding of vendace, Coregonus albula (L.), larvae in net enclosures

Vendace, Coregonus albula (L.), larvae reared in net enclosures anchored in the littoral zone of Lake Ylä-Enonvesi, eastern Finland, were observed for a period of 44 days in order to determine the effects of density on mortality, growth and feeding of the larvae. The ratio of newly-hatched fish to their food was regulated by controlling the number of fish stocked into the enclosures. Prey animals were expected to move freely in and out of the enclosures. The effect of nylon mesh (500 μm) on the penetration of zooplankters into the enclosures was negligible. The influence of possible starvation was determined by analysing the growth of the larvae, their Fulton condition factor, the instantaneous amount of food ingested, and the food composition in their guts. All these indicators were inversely correlated with larval density. Vendace larvae were found to be resistant to mortality from direct starvation. At all densities the survival rate was over 60%. At the time of complete yolk absorption, there was no increase in mortality.     

Effects of invading vendace (Coregonus albula L.) on species composition and body size in two zooplankton communities of the Pasvik River System, northern Norway

Species composition and body-size distribution were studiedin the crustacean zooplankton communities of two limnologicallysimilar lake localities situated 50 km apart in the Pasvik RiverSystem, northern Norway. A recent invasion and successive downstreamexpansion of vendace (Coregonus albula), a specialized zooplanktivorousfish, allowed comparisons between sites with different predationpressures. Vendace had established a high population densityand was the dominant fish species in the pelagic of the upperlocality, but had just invaded the lower locality with a smallnumber of individuals. Whitefish (Coregonus lavaretus), a closelyrelated but less specialized zooplanktivore species, dominatedthe native fish community of both lakes. The zooplankton communityof the upper locality was dominated in June and August by Bosminalongirostris, the smallest zooplankton species represented inthe water course, and in September by Daphnia cristata. Thelower locality was dominated by the larger Holopedium gibberumand Eudiaptomus graciloides in June, by D.cristata in August,and by D.cristata and B.longirostris in September. The meanbody size of the three most abundant cladoceran species wassignificantly smaller in the upper locality, compared to thelower locality. It was concluded that the invasion and establishmentof a dense vendace population in the upper locality had increasedthe predation pressure in the pelagic, resulting in a reductionof body size and a shift towards smaller species in the zooplanktoncommunity.     

Digestion of zooplankton in the alimentary tract of vendace (Coregonus albula) larvae

The degradation of zooplankton eaten by vendace larvae was investigated by cutting their tubiform alimentary tract into four quarters and analysing the contents separately. Soft-bodied rotifers were found to degrade and become indistinguishable in the anterior part of the alimentary tract, while cladocerans and copepods could still be identified in the posterior part. Assessing the diet of a larva on the basis of its whole alimentary tract contents was found to give biased results. More reliable estimates of the proportions of zooplankton taxa in the diet could be achieved from the first quarter of the alimentary tract.     

The use of live and frozen Artemia salina nauplii enriched with fluorochromes for mass‐marking vendace Coregonus albula (L.) larvae

The aim of this study was to investigate the use of Artemia salina nauplii enriched with chosen fluorochromes for mass marking vendace Coregonus albula (L.) larvae. In the experiment, vendace larvae (6 DPH) were fed with live or frozen A. salina nauplii immersed in tetracycline hydrochloride (TC), calcein (Cal) or alizarin red S (ARS) for four subsequent days. More successful effects (marking otoliths) were obtained by feeding the fish with live nauplii enriched with fluorochromes, regardless of the dye type. The highest percentage of marked otoliths (100%) was recorded in the group fed with live nauplii immersed in TC. In the groups fed live or frozen nauplii enriched with Cal and ARS, a lower percentage of marked individuals (63.3%–73.7% and 56.7%–63.3%, respectively) were recorded. The survival rate of vendace larvae in particular groups oscillated between 93.7% and 95.7%. There were no significant differences in the total body length and body weight of the reared vendace larvae among different groups. In conclusion, for mass marking of vendace larvae using a feeding method, fish fed A. salinalive nauplii enriched with TC at a dose of 600 ppm is recommended for fishery practice.     

Food and food selection of cisco (Coregonus albula L.) in a dysoligotrophic lake

With minor exceptions, cisco (C. albula) in Lake Suomunjärvi fed on cladocerans and copepods. The food habits were different among two size classes of fish. The composition of cisco diet changed at different depths and times of the day, but the distribution of zooplankton was usually very similar in each period irrespective of the depth or diel period. Daphnia, Bosmina, Cyclops scutifer and Heterocope appendiculata were the main diet of cisco. Calculations of fish electivity indices showed that cisco selected usually large species of cladocerans and copepods and a small cladoceran, Bosmina coregoni. Body-size selection was clear for Daphnia and Bosmina.     

Polymorphism and structure of the population of Proteocephalus longicollis Zeder, 1800 (Cestoda: Proteocephalidae) in the vendace Coregonus albula L

Polymorphism and phenotypic diversity of a hostal ecoform of Proteocephalus longicollis from its typical host, the vendace, Coregonus albula L., were studied. A complex phenotypic structure of the parasite population and presence of morphologically different groupings were revealed. We distinguished four groupings based on the external characters and three groupings based on the feed and reproduction features; among latter groupings one has very specific variations of features. We conclude that P. longicollis has high intraspecific and intrapopulation heterogeneity, and the host plays a stabilising role in the parasite species formation.     

Comparative study of bile-acid composition in the bile of the European vendace Coregonus albula L. and whitefish Coregonus lavaretus L. under conditions of technogenic water pollution

Changes of the bile acid composition were studied in bile of the vendace Coregonus albula L. and the whitefish Coregonus lavaretus L. under effect of sewers of an ore mining and processing plant, the main pollutin agents of the sewers being heavy metals. The revealed variability of the bile acid composition indicates different species-related sensitivity to the studied pollutants as well as a lower resistance of males as compared with females to this type of pollution. Mechanisms of effects of industrial sewers on the bile formation processes and a possibility of using parameters of the steroid lipid metabolism at evaluation of the state of water ecosystems are discussed.     

Survival of Coregonus albula (L.) (Teleostei) embryos incubated at different thermal conditions

Eggs of Coregonus albula were incubated at constant temperatures: 1.1, 2.0, 2.9, 4.9, 6.6, 8.4, and 9.9 °C, and the percentage of normal hatch was 20.6, 11.8, 30.4, 61.0, 51.7, 32.6, and 14.6%, respectively. The lower and upper median tolerance limit (TL 50) defined as the interpolated temperature at which embryos survival to hatch was 50% of the highest response (61% at 4.9 °C) were 2.9 and 8.5 °C, respectively. The optimum temperature range delimited by lower and upper TL 75 was encompassed by 4.0 and 7.2 °C.Eggs of C. albula incubated at variable temperature in a commercial hatchery showed a very high survival (up to 76%). Similarly low survival observed during hatching of embryos at constant temperatures of 1.1 and 2.0 °C could be hightened (to about 90%) by raising the temperature in the beginning of hatching period. This phenomenon was utilized in the technique of delaying C. albula embryos' mass hatching for the purpose of synchronization in time of stocking the lakes with the time of appearence of good thermal and food conditions for C. albula larvae.The conception of the optimal thermal conditions for Coregoninae embryogenesis was developed as the course of incubation temperature, securing the highest survival rate during embryogenesis and also during the larval period.     

Utilization of body stores in embryonated ova and larvae of two coregonid species (Coregonus lavaretus L. and C. albula L.)

• 1.1. Developing eggs of whitefish (Coregonus lavaretus L.) and vendace (Coregonus albula L.) were kept at 1–2°C and some eggs taken gradually up to 8°C to provoke mass hatching of embryos.
• 2.2. Wet weight, dry matter and the contents of lipid, protein and ash were measured in fish during the course of experiment.
• 3.3. Dry matter content decreased gradually in whitefish eggs from 15.64 to 11.95% during 1 month at 1–2°C, whereas vendace eggs showed only a slight decrease from 16.27 to 15.53%.
• 4.4. In both species protein content decreased but lipid increased when approaching the natural time of hatching.
• 5.5. During delayed hatching at low water temperatures protein contributes to catabolism, whereas lipid content decreased only in the later phase of the experiment.
• 6.6. Larvae starved for 10 days after hatching lost increasing amounts of dry matter (from 26.1 to 50.3% of body weight) and protein (from 18.7 to 45.9% of body weight) as they remained longer in cold water as embryos.
• 7.7. A correspondence was found between assessment of metabolic utilization of body stores based on chemical analysis of fish body and previous work on oxygen consumption and nitrogen excretion.

     

Populational variability of Proteocephalus longicollis (Cestoda: Proteocephalidae) in the vendace Coregonus albula from lakes of Karelia

Populational variability of Proteocephalus longicollis from the vendace inhabiting various types of Karelian water bodies was studied. High phenotypic diversity of the helminth and polymorphism in the cestode's major functional complexes - attachment, trophic and reproduction - are established. High degree of phenotype pool realization was determined for various P. longicollis populations. Traits belonging to different functional complexes were shown to have different variability patterns. The highest stability was shown for the attachment organs of P. longicollis, which had similar values of qualitative indices and nature of variation. The traits of the trophic and reproduction complexes are more variable. The conclusion was made that the high intrapopulation diversity of P. longicollis is a response to high ecological variability of the vendace, and the distinctions in the phenotype variability of the helminth reflect the differences between population development patterns of the parasite (cestode P. longicollis) and its host (vendace Coregonus albula) in lakes of Karelia.     

Population regulation of vendace (Coregonus albula) in Lake Pyhäjärvi, southwest Finland

Previous time series analysis on vendace population dynamics in Lake Pyhäjärvi, 1971–1990, revealed a 2-year cycle in year-class strength, implying powerful density-dependent regulation. Here we have extended this analysis by using multiple regression models to test whether the recruitment series is influenced by density-independent factors. We chose population size with a lag of 1 year as the density-dependent factor; the density-independent factors were the summer water temperature with a lag of 2 years (temperature sum for June, July and August, indicating the year-class strength of predators) and the temperature-derived length of the larval period of vendace. For the years 1972–1990 the coefficient of determination ( r ²) of this regression model was 0·77. We suggest that the basic mechanism producing a persistent 2-year cycle of vendace in Lake Pyhäjärvi is the asymmetrical food competition between age groups. The abundance of predators in the lake and the warming of the water after the hatching of larvae in spring together determine the final year-class strength of vendace.     

Year-class fluctuations in vendace,Coregonus albula (Linnaeus): Who's got the upper hand in intraspecific competition?

The vendace Coregonus albula (L.) populations in the lakes Mjøsa and Osensjøen exhibited fluctuating year-class strength. In Mjøsa, a strong year-class emerged every third year, except for the four year period between the strong year-classes 1969 and 1973. The difference between the strong and weak year-classes decreased from the 1960s, through the 1970s to the 1980s. The Mjøsa vendace matured sexually at age 2 +, and more than ten sexually mature age-groups were present in the population. Growth ceased at maturation, and asymptotic length was 23.6 cm. In Osensjøen, one strong year-class (1969) dominated the population during the period 1976–1987. The Osensjøen vendace matured sexually at age 3, and more than 15 sexually mature age-groups were present in the population. Growth ceased at maturation, and asymptotic length was 28.4 cm. In both lakes, vendace fed on crustacean zooplankton in the epilimnion throughout summer and autumn. Our data indicate that regular year-class oscillations occur as a result of the juvenile survival being negatively correlated to the number of adults.     

Reproductive strategy and spawning activity of the European hake Merluccius merluccius (L.) in the Bay of Biscay

Histological examination of ovaries from European hake Merluccius merluccius from the Bay of Biscay sampled on a monthly basis from December 1996 to October 1997 demonstrated that European hake exhibit indeterminate fecundity. Oocyte development is asynchronous with a continuous oocyte size-frequency distribution in prespawning, spawning and postspawning females, and a gradual decrease in the mean diameter of advanced yolked oocytes as spawning proceeds. Spawning European hake were observed throughout the 11 month study period. The spawning fraction ranged from 0·085 to 0·207, which is equivalent to a batch interval of 5–12 days. The spawning fraction and proportion of spawning females were highest from January to March. Seasonal variation of atresia was inversely related to spawning fraction. Extensive atresia in individual fish was observed in September and October, when the spawning fraction was low.