Maturity, sex ratio and spawning time of Mugil cephalus Linnaeus from the Bulgarian Black Sea coast

Abstract

Aspects of the reproductive biology of Mugil cephalus from the areas of Bulgarian Black Sea coast were studied between May 2010 and Jun 2013. Altogether 359 specimens of M. cephalus have been used to determine the main population-biology parameters, representing the reproductive potential of the fishes. The sex ratio of males : females in sexually mature part of the population is 1 : 1 (χ² = 0.61 < χ²_st = 10.83 (P = 0.001)). The females are matured at the third year, while the males at the second year, with a minimum length of 19.5 cm and 16.9 cm and a minimum weight of 136.3 g for males and 60 g for females. The spawning period of an M. cephalus in the areas of the Bulgarian Black Sea coast starts from Jun to September with a peak in July. Gonad maturation has been studied separately for both sexes by the use of the gonadosomatic index (GSI = g/W*100) and the coefficient b from the equation g=a+b*W (g – gonad weight, g; W – fish somatic weight, g). It was determined the annual dynamics of GSI. The maximum values for the ovarian GSI are established in August while for the testes in July. Its values increase with the fish weight and range from 1.19 to 5.37 for females and for male the range it was from 0.51 to 7.48.