Age, reproduction and fecundity of the spined loach Cobitis taenia L. (Pisces, Cobitidae) from Lake Klawój (Poland).

This is the first study concerning the features of the reproduction process of the karyologically identified spined loach C. taenia (2n=48). The histology of 71 ovaries, and gonadosomatic index (GSI) of karyologically identified spined loach Cobitis taenia L. from Lake Klawój (Northern Poland) were examined. The absolute and relative fecundity of 25 females was estimated by gravimetric method. The age of fish was determined according to the annual increments of otholits. The spawning of C. taenia from Lake Klawój took place from May to July, at a water temperature exceeding 18.5 degrees C. The GSI values at the beginning of the reproduction period ranged from 7 to 19%. The average absolute fecundity of females was 2078 eggs, with the number ranging from 869 to 3371 eggs. High individual variability in the gonad histology and the GSI values during the reproductive period was observed. Such variability could be the result of beginning the reproduction process in the fish at various times and, probably, due to the various numbers of batches laid and various numbers of eggs per batch.