Annual cycle in female minnows Phoxinus phoxinus (L.) from an upland Welsh lake

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Abstract
A population of Phoxinus phoxinus in a small, upland, Welsh lake was sampled at monthly intervals between February 1976 and January 1977. Mature females belonged to the 1972, 1973 and 1974 year classes. Spawning took place in May and June over gravel at the lake's edge. Regression analysis provided estimates of the mean carcase, ovary and liver weights expected for a female of length 65 mm. The ovarian weight increased rapidly in spring but dropped sharply between May and August. Carcase and liver weight declined during the breeding season, but recovered rapidly on completion of breeding. The increase in the weight of the ovary was accompanied by an increase in the proportion of dry matter, while the carcase and liver became relatively hydrated during the breeding season. Also at this time, the energy and lipid content of the carcase was low, but the ash content was high. Thus ovarian maturation and breeding were associated with a depletion of the carcase and liver, but this was quickly reversed at the end of the breeding season. Preliminary estimates of the changes in total energy in the ovary and carcase during ovarian maturation were made which suggested that the decline in the energy content of the carcase represented a significant proportion of the gain in energy content of the ovary. The sampling period coincided with an unusually severe drought and the possible consequences of this on the population are considered.