The Body Composition of Adult Perch, Perca fluviatilis in Windermere, with Reference to Seasonal Changes and Reproduction

Abstract

Proximate analyses were carried out on both the soma and gonads of adult male and female perch caught in Windermere [England] from Sept. 1973-July 1976. Non-protein N to total N ratio of the soma of both sexes was 0.1580. Non-protein N of the gonads varied with the season. Energy values of somatic tissues based on conversion factors were higher than those obtained by calorimetry. The length-weight relationships were determined for each sex and monthly weights of the soma and gonad for a standard male (22.5 cm) and standard female (26.0 cm) were calculated. Seasonal trends were apparent. The testes, although ripe in April, were heaviest during Oct. (8.75% of the total body weight). The ovary developed in size up till spawning when it reached 16.91% of the total body weight. Monthly weights of body constituents for standard fish were calculated from regression lines. There was heterogeneity between monthly regression lines of water, fat and protein on weight for male soma. The energy content of the standard male soma was highest in Sept. (5.91 kJ/g wet weight), and lowest in Dec. (4.53 kJ/g wet weight). Although the male soma increased in weight during Aug., the energy content dropped. The weight of constituents of the testes varied with stages of maturation. The percentage weight of fat in the testes remained constant (3.5% wet weight, for a standard fish). There was homogeneity between monthly regressions for water, fat and protein for female soma and the energy content of the standard female soma was constant (5.32% kJ/g wet weight) throughout the year. The wide variation in the fat content of female perch for any 1 mo. was partly due to the age-class structure of the catch, fat content decreasing with age. There was a regular increase in water, fat and protein from 1st stages of ovary development until ripe. A sharp increase in the percentage weight of water in the ovary took place after spawning. Energy lost at spawning by the gonads as a percentage of that lost by the soma for the year was 9.6% in the male and 87.1% in the female. Equations were calculated to determine the relationship of percent fat, percent protein and energy (kcal/g dry weight) with percent water for the soma of all fish. All equations showed an inverse relationship between the 2 variables considered. An equation (E = 0.880902 + 4.029492 K) was developed to calculate the energy content (E) (in kcal/g) of the soma of perch from its condition factor (K). The condition factor was based on K.female. = W/0.01410 L2.91925 and K.male. = W/0.00609 L3.17514.