Exceptionally big individual perch (Perca fluviatilis L.) and their growth

In Lake Windermere (U.K.) where there was a dense, slow-growing population of perch ( Perca fluviatilis L.) which had an l _x of about 180 mm, there co-existed a few individuals with an l _x of 463 mm. Data from 137 of these big perch, mostly caught in gillnets fishing for Esox lucius L., were examined. Their early growth was identical to that of normal perch, but, at an age, varying between individuals, from 1 to 8 and averaging 4 years, their growth accelerated for about 4 years and then followed a von Bertalanffy model with an l _x of 463 mm. They thus had a 'double' growth-curve that is revealed only if individual growth is examined. Acceleration tended to occur in certain calendar years and was correlated with strong year-classes of young perch. Growth was greater in years with warm summer water temperatures. There were no changes in the growth of big perch, after they had achieved 290 mm, during a period of great changes in the population density and an increase in the growth of normal perch < 290 mm. No more big perch were caught in Windermere between 1967 and 1990. Net selection, length-weight relationships, seasonal cycle in gonad weight, and opercular-body length relationship were the same as those of normal perch. The few available data suggest that big perch were piscivorous, feeding largely on small perch. The distribution of sites in the lake where big perch were caught is contagious, catches follow the negative binomial; but within fishings that caught big perch at the same site and time, catches were more evenly distributed than random. It is postulated that most adults would have accelerated their growth if they had sustained piscivory. Similar big perch have been found in other lakes.     

Seasonal changes in growth and standard metabolic rate of juvenile perch, Perca fluviatilis L.

The maximum growth rate of juvenile perch, PercaJuviatilis L., at different constant temperatures and in naturally changing day-lengths was studied in the laboratory. Standard metabolic rate was studied in starvation experiments at constant temperatures under short- and long-day conditions. Growth occurred in temperatures above 8 to 10°C. In winter, from mid-October until mid-April, maximal growth was considerably reduced and was relatively slow but constant. The standard metabolic rate was reduced c . 50% under short-day conditions. The seasonal change in metabolic rates, presumably controlled by an endogenous rhythm, was considered to be an adaptation to low food availability during the short winter days.     

Exceptionally rapid growth and early maturation of perch in a freshwater lake recently converted from an estuary

In the recently freshened Volkerak, in the SW Netherlands, age 0-2 perch attained mean lengths of 12, 24 and 30 cm fork length. Males matured at age 0 and females at age 1. This exceptionally rapid growth and early maturation was due to abundant availability of zooplankton and Neomysis integer , at low fish biomass during change from a marine towards a freshwater fish community.     

An application of a bioenergetics model to Eurasian perch (Perca fluviatilis L.)

A bioenergetics model was developed for Eurasian perch ( Perca fluviatilis L.) by revising an existing model for yellow perch and walleye. Data were gathered from field studies and the literature. Besides adjusting the original parameters of the model, effects of season on consumption and metabolic rates were added. The predictive capability of the revised model was high both concerning the levels of growth and its seasonal development in the Baltic coastal waters to which the model was applied. Perch young-of-the-year attained almost maximum consumption and growth except in the highest temperatures experienced. In larger fish, the model estimated consumption to be about 50 per cent of the maximum possible rate.     

Delayed spawning of perch, Perca fluviatilis L., in acidified lakes

The timing of spawning of perch was examined in four acidified lakes (pH 4.4–4.8) and in one circum-neutral lake (pH 6.3) in southern Finland in spring 1987. In three of the lakes, perch started to spawn soon after the ice melt (4–14 degree days > 5° C) and had spawned by the end of May at about 100 degree days > 5° C. In the two most acidified lakes, fish started to spawn later, at 35 and 60 degree days > 5° C, and had spawned in early June, at about 200 degree days > 5° C. The maturing of gonad products was delayed in both males and females.     

Resistance of perch eggs to attack by aquatic fungi

In the distinctive gelatinous Perca fluviatilis egg mass, limited fungal growth by Aphanomyces and Saprolegnia spp. especially S. diclina , occurred within dead eggs but did not spread to adjacent live eggs. Perch eggs exposed to parasitic challenge by Saprolegnia parasitica , S. dieclina (type III) and S. ferax , under fluctuating temperature regimes replicating spring water temperatures, did not have significantly greater mortality than did unchallenged controls. The observations suggest that perch eggs have some anti-fungal properties which usually prevent the spread of fungus throughout the egg mass and that under normal spring temperatures there should be negligible ecological consequences of fungal infection in perch egg masses.     

Length and weight changes in 0+ perch, Perca fluviatilis L., following fixation in formalin

Significant shrinkage and increase in weight followed fixation of 0+ freshwater Perca fluviatilis in formalin. Conversion values to obtain live values should take account of formalin concentration, fish size and holding time of preserved fish prior to measurement.     

Omitted spawning in compensatory-growing perch

Individual growth trajectories of perch Perca fluviatilis in a Swedish forest lake (sampled in March) revealed growth depression at intermediate sizes, followed by enhanced, compensatory growth at larger sizes. All males of age ≥3+ years had mature, almost ripe testes. The proportion of spawning females was higher at age 3+ years (79%) than at older ages (44%), indicating that older females with non-developing ovaries were resting rather than immature juveniles. Resting females were 175–247 mm in total length ( L _T), and they were usually in a state of increasing annual growth. Spawning females were of more variable size (123–418 mm), and the larger ones had entered the faster growing state ≥2+ years before catch. Detectable growth costs of spawning indicated that resting females made a trade-off between current and future reproduction, rather than being constrained by poor feeding conditions.     

The distribution and abundance of young (I +–II +) perch, Perca fluviatilis L., in a deep eutrophic lake, England

Seasonal changes in the vertical and horizontal distribution of young (I +–II +) perch in Rostherne Mere, a deep (max. depth 31.0 m) eutrophic lake are described using sonar. During the summer (June–August), perch were present within the thermocline (9–14° C) between 7 and 10 m. There was no significant difference between samples during this period, nor was there any evidence of shoaling. From September onwards perch moved into deeper waters. By late winter fish had become patchy in their distribution. Total numbers, during the summer, were estimated to be 988 ha ¹ with 95% confidence limits of ±115 (biomass 98.8 kg ha ⁻¹). Densities (no. m⁻³) fell by over 90% after the autumn overturn. The implications for predators are discussed. Acoustic sampling provides a useful, non-destructive method of sampling eutrophic lakes on a routine basis. Information obtained is of ecological, behavioural and physiological interest.