Growth Of Whitefish Research Articles

The influence of population density on growth of whitefish ( Coregonus lavaretus L.) in four prealpine lakes

In the early 1990s whitefish ( Coregonus lavaretus L.) of Ammersee, a prealpine bavarian lake, showed extremely poor growth. The average weight of 3+ whitefish was lower than 150 g in 1994. But in 1994 the trend changed. Growth of whitefish doubled between 1994 and 1999. The average stomach contents also showed a significant increase in the course of recent years. Parallel to the weight increase a distinct decrease in population density could be seen, monitored with a SIMRAD EY 500 echo sounder. In the first half of 1999, there were about 350 fish per hectar (F ha −1) in Ammersee. That was only about a fifth of the number at the end of 1995. In 1996/97 fish density in a nearby prealpine lake, oligotrophic Walchensee, was clearly lower with fewer than 350 F ha −1 than in Ammersee (mean value 1996: approx. 850 F ha −1, 1997: approx. 770 F ha −1). Despite the lower trophic status, Walchensee whitefish showed clearly better growth: the average weight of 3+ whitefish was 308 g. At the same time the weight of 3+ whitefish of prealpine Kochelsee was 260 g on average. There was an extended food resource for Kochelsee whitefish with the additional possibility of feeding on benthic prey. In comparison to Ammersee this could explain the significantly better growth of Kochelsee whitefish despite an even higher fish density (approx. 1300 F ha −1 in 1996/97). Chiemsee, another prealpine lake, is very similar to Ammersee in relation to fundamental limnological parameters and was studied in 1993 and 1994. In 1994 fish density of Chiemsee was at a maximum of approx. a fifth of that of Ammersee, and whitefish growth was significantly better. 3+ whitefish weighed above 300 g, about double the weight of Ammersee whitefish at that time. A comparison of mean stomach contents of whitefish in both lakes points to intraspecific food competition in Ammersee. Those results indicate a causal connection between whitefish density and growth.

Post-stocking perturbations in a population of subarctic whitefish, Coregonus lavaretus (L.): Effects on growth, condition and cestode infection

Lake Kilpisjarvi was stocked with a total number of 440 000 migratory and benthic whitefish fry during the period of 1959–1964. Thereafter, the Diphyllobothrium ditremum plerocercoid infection became a problem decreasing the feasibility and commercial exploitation of the whitefish stock. Since dense fish populations may cause stunting, all stockings in the study area were stopped in an attempt to enhance the fisheries. The aim of the present study was to explore the effect of the cessation of the stocking on the growth, condition, catches and D. ditremum infection of the whitefish population. A total of 1594 whitefish were sampled with benthic gill nets. Growth was estimated from length-at-age and mass–length relationship was estimated with a non-linear regression in 1982–1983, 1992–1993 and 1997. Parasite infection was studied in 1992–1993 and 1997. Growth and condition were poor in the beginning of the 1980s. In 1992–1993, the growth and condition of the fish improved as the numerical catch per unit effort decreased from 1982 to 1992. The mean catches of other fish species were low. There were no significant changes in whitefish growth or condition from 1992–1993 to 1997. From the 1970s to 1982–1983, during slow growth and poor condition of the fish, the median gillraker count was decreasing to 19 (min–max 14–26). In 1992–1993, the gillraker count had increased significantly to 23 (min–max 19–26). However, the improved growth and condition did not cause decrease in the D. ditremum burden. On the contrary, based on our own results and literature notes, the parasite abundance seems to increase during the observation period of 1964–1997.

Diet, growth and competitive abilities of sympatric whitefish forms in a dense introduced population: results of a stocking experiment

The food of five whitefish stocks Coregonus lavaretus planted in Lake Vuokalanjärvi consisted mainly of zooplankton and insects taken from the water surface. The amount of benthic food in the diet of the two sparsely gill‐rakered (23 and 28 rakers) stocks increased from the age of 2 years onwards. The growth of whitefish was slow in all stocks. The densely gill‐rakered stock (50–51 rakers) originating from the same lake system as Lake Vuokalanjärvi grew faster than the other stocks, and the food consumption of 4‐ and 5‐year‐old fish belonging to this stock was nearly double compared with the other stocks. The habitat choice of the whitefish differed between the stocks even in the densely‐rakered stocks classified as the same form. A stock with flexible habitat use and feeding habits is most likely to succeed. Introducing whitefish stocks from distant areas is not advisable.

Accumulation of plerocercoids of Triaenophorus crassus in the second intermediate host Coregonus lavaretus and their effect on growth of the host

Patterns of accumulation of Triaenophorus crassus in its second intermediate host whitefish Coregonus lavaretus s.l. were studied between 1991 and 1996 from two host populations in two separate areas of Lake Saimaa, Finland. Whitefish were infected commonly with several T. crassus plerocercoids and the parasites were aggregated into the oldest hosts. In one host population the annual parasite accumulation was 0·9 parasites in all host age groups between 3 and 8 years. In the other host population the annual accumulation was 1·6 parasites in 3–5‐year‐old fish, but increased up to 3 to 4 parasites per year in fish over 5 years old. The increase did not coincide with the period of maturation or any increase in whitefish growth, both of which could alter the food intake of the fish. The sharp increase in the annual accumulation suggests a threshold intensity above which the probability of acquiring further parasites increases. In spite of a heavy aggregation of parasites there was no evidence of parasite‐induced host mortality. The annual increase in mean abundance was not correlated with the mean annual weight increase in 2–4‐year‐old fish within cohorts. However, evidence of a negative effect of parasites on whitefish growth was revealed by back‐calculation of lengths of uninfected and infected whitefish and correlations between length or weight of fish and intensity of infection with fish age. Both analyses suggested that larger young fish harboured more parasites than the smaller ones while in older fish the reverse was true, a pattern that has not been shown earlier for parasitized fish.

The growth of whitefish in relation to water quality and fish species composition

Water quality in 16 Finnish lakes did not affect directly densely gill‐rakered whitefish growth, except possibly in an acid (pH 4·9) lake, Iso Lehmaälampi, where acidity may have retarded the growth of whitefish. The density of roach affected whitefish growth in the second year of life: highest growth rates were in lakes without a roach population and lowest growth rates in lakes having strong roach populations. Competition by vendace also retarded the growth of young whitefish. The efficient mass removal of roach from a eutrophic lake was considered to have increased the growth rate of young whitefish. It is suggested that an examination of the fish species composition and relative abundance, as well as the growth of whitefish, can be used as an aid in predicting the success of stocking with whitefish.

The growth of whitefish in relation to water quality and fish species composition

The growth of whitefish in relation to water quality and fish species composition

Feeding and growth of whitefish fed restricted and abundant rations: influences on growth heterogeneity and brain serotonergic activity

The whitefish, Coregonus lavaretus, is a schooling species, and it was hypothesized that, when faced with feed restriction, the behaviours associated with a schooling habit would lead to there being less heterogeneity in feeding and growth than has been observed in other members of the Salmonidae. This was tested by monitoring the feeding, growth and brain serotonergic activity of whitefish subjected to different levels of feed restriction (full rations and regimes estimated to give a 25 and 50% reduction in growth rate). The feed restrictions were successful in reducing rates of feeding and growth, but these reductions were not accompanied by any marked increases in interindividual variations in either feed intake or growth rates. Consequently, the imposition of restricted feeding regimes did not result in an increase in the size variation of fish within rearing tanks. Further, the brain serotonergic activity (assessed as 5‐HIAA: 5‐HT ratio) of individual fish was not found to correlate with either their feed intake or growth rates. This suggests that any competition resulting from restricted feeding did not lead to the establishment of marked dominance‐subordination relationships. 5‐HIAA: 5‐HT ratios were, however, higher amongst fish fed the most restricted rations than in fish of the other groups. This may have been a reflection of a general nutritional stress rather than pointing to an increase in social conflict amongst the fish fed the lowest rations. When provided with abundant rations the fish that had been feed‐restricted responded by becoming hyperphagic and showing catch‐up growth, the degree of compensation being related to the severity of the previous food restriction. Taken together the results suggest that restricted feeding may be a suitable method for controlling rates of production of whitefish, without there being a high risk of a marked increase in size variation with the passage of time.

Feeding and growth of whitefish fed restricted and abundant rations: influences on growth heterogeneity and brain serotonergic activity

Feeding and growth of whitefish fed restricted and abundant rations: influences on growth heterogeneity and brain serotonergic activity

Influence of the length of the daily feeding period on feed intake and growth of whitefish, Coregonus lavaretus

A study was carried out to examine the influence of the length of the daily feeding period on feed intake and growth of whitefish (initial weight 60–90 g), with the aim of providing guidelines as to the feeding regimes to be used when cultivating this species. Fish were held at 14.5 °C under a 24L:0D photoperiod. Following a period during which fish were fed throughout the day, feeding regimes of 6, 12, 18 or 24 h feeding per day were imposed on 3 tanks of fish per treatment. These feeding regimes were maintained for 6 weeks during which feed intake (3 times by X-radiography) and growth were monitored. When feeding was restricted to 6 h each day daily intake tended to be initially reduced, but by the end of the experiment daily feed intake did not differ between groups of fish held on the different feeding regimes. This indicates that the fish fed according to the time-restricted regimes were able to compensate for the reduced length of the feeding period, but some weeks were required before the compensatory mechanisms took full effect. Time-restricted feeding also resulted in fish on the 6 h regime having significantly lower rates of growth (0.98 ± 0.08% d −) than those on the 24 h regime (1.42 ± 0.14% d −1) early in the experiment. During the latter stages of the experiment, there were no significant differences in growth rates amongst the fish fed according to the different regimes. The differences established early in the trial were still apparent after 6 weeks, with overall rates of growth for the entire trial period seeming to be directly related to the length of the feeding period (6 h: 1.27 ± 0.09% d −1; 12 h: 1.39 ± 0.06% d −1; 18 h: 1.46 ± 0.19% · d −1; 24 h: 1.65 ± 0.05% d −1). However, the only significant differences recorded were between the 6 and 24 h feeding regime groups. Length of the feeding period was not found to have any significant effect upon feed conversion, although there was a tendency for the feed:gain ratio to be lowest in the groups of fish fed according to the time-restricted feeding regimes (6 h: 0.57 ± 0.05; 12 h: 0.58 ± 0.06; 18 h: 0.65 ± 0.07; 24 h: 0.64 ± 0.08). The results indicate that whitefish are flexible in their feeding behaviour, and adapt readily to imposed regimes over a period of a few weeks. These modifications to feeding responses result in good growth performance and good feed conversion.

Long-Term Cyclical Trends in Growth of Lake Whitefish in South Bay, Lake Huron

A 39-year series of samples (1947–1985) was obtained with gill nets and trawls from a discrete population of lake whitefish Coregonus clupeaformis within the innermost basin of South Bay, Manitoulin Island, in northern Lake Huron. Back-calculations based on scales allowed growth in weight to be estimated for 47 year classes of lake whitefish. Growth of young fish prior to entry into exploited sizes was slow in the mid-1930s, increased to a maximum in the early 1950s, declined again to a minimum in the late 1960s, and increased again during the 1970s and early 1980s. Trend analyses with Fourier transformations provided cyclic sine wave models with a 32-year period that fit growth trends better (higher r2) than either linear or polynomial models. Long-term cycles in water level and temperature correlate significantly with the observed growth cycle. These two environmental factors account for 88% of the variation in lake whitefish growth, leaving 12% to be accounted for by community interactions. Based on observations in South Bay and fishery studies in other areas of the province, a hypothesis is suggested that long-term fluctuations in the hydrological cycle and other climatic factors interact to control long-term fluctuations in fish production throughout Ontario.

Age and Growth of Whitefish, Coregonus Clupeaformis (Mitchill), in Big Bay De Noc and Northern Lake Michigan

Abstract On the basis of age-composition of fish taken by commercial nets in 1949 and 1950, the whitefish in Big Bay de Noc, in the upper Michigan peninsula, appear to be a population separate from that of northern Lake Michigan. There was a change in the age-structure of the commercial catch of whitefish in Big Bay de Noc during the period 1949 to 1954. In 1949 and 1950, several year-classes made important contributions to the catch, but after 1950, Age-III fish provided 85 to 90 percent of the annual catch. Possible reasons for this change in age-structure of the catch are discussed. With the exception of two localities in northern Lake Michigan, growth rate of whitefish in Big Bay de Noc and in the lake was similar. Annual differences in growth in Big Bay de Noc were noted. Fish of the larger year-class of 1949 showed greater first-year's growth than other year-classes, suggesting that the factors responsible for good growth may also favor high survival. Whitefish of older age-groups also showed indica...

Rapid electrolysis without rotating electrodes: Graham Edgar and P. B. Purdum, of the University of Virginia ( Jour. Am. Chem., Soc., 1922, xliv, 1267–1270)

Lake whitefish (Coregonus clupeaformis Mitchill), an important commercial species in the Laurentian Great Lakes, have experienced decreased growth and condition in regions of the upper Great Lakes over the past 20 years. Increases in lake whitefish density and decreases in the density of Diporeia spp., an energy rich and historically important part of the lake whitefish diet, have been implicated in the recent declines in lake whitefish growth and condition. The goal of this study was to describe lake whitefish fecundity, egg lipid content, and total ovary lipid content in selected regions of Lakes Huron, Michigan, and Superior in 1986–87 and 2003–05, two time periods with different lake whitefish and Diporeia densities. Under conditions of high lake whitefish density and low Diporeia density, female lake whitefish in the upper Laurentian Great Lakes generally produced fewer eggs. Egg lipid content was higher in 2003–05 than in 1986–87 at all sites, regardless of changes in lake whitefish or Diporeia densities. Total ovary lipid content and lake whitefish abundance were inversely related, while there was no significant relationship between total ovary lipid content and Diporeia density. The amount of energy that lake whitefish invested in egg production was more closely associated with lake whitefish abundance than with Diporeia density. This study provides evidence that recent changes in production dynamics of Great Lakes lake whitefish have not been driven solely by declines in Diporeia but have been significantly influenced by lake whitefish abundance.