Abstract
The reproductive biology of round sardinella, Sardinella aurita Valenciennes, 1847, was studied for the first time in the north-eastern Mediterranean Sea. Round sardinella has gained much attention lately because of its biomass increase, which might be the result of climatic changes occurring across the Mediterranean Sea. Monthly samples were collected on board commercial purse-seiners for two complete year cycles (September 2000 to August 2002). Round sardinella is a gonochoristic fish. The overall female to male ratio was not statistically different (P=0.34) from unity, although it varied monthly and with the length of the fish. The seasonal changes in the gonadosomatic index and the macroscopic characteristics of gonads showed that round sardinella in the northern Aegean spawns between May and July. Male round sardinella reach first sexual maturity at a smaller total length than females (155.0 and 168.3 mm respectively). Mean absolute fecundity (FA) increased exponentially with body length (FA=0.0949xL4.22) and weight (FA=511.19xW1.02), with an average of ~21,000 oocytes produced per spawning female. Relative fecundity (FR) ranged between 242 and 681 oocytes/g of body weight (average: 445 oocytes/g). The frequency distribution of oocytes showed that round sardinella produces a single batch of oocytes. In general, the reproductive characteristics of round sardinella in the north-eastern Mediterranean Sea differed when compared to stocks from other areas of its distribution.
Highlights
Fish have developed reproductive strategies and traits that ensure the survival of the species under variable and often unfavourable conditions (Potts and Wootton, 1984)
The reproductive strategy of each species is expressed by certain characteristics such as age and size fecundity, time duration and frequency of spawning, size at first maturity and reproductive behaviour
The aim of the present study is to investigate the following aspects of the reproductive biology of round sardinella in the northern Aegean Sea: (a) the time and duration of the spawning season; (b) the annual reproductive cycle, in terms of seasonal changes in the gonadosomatic index and maturity stages; (c) the sex-ratio; (d) the size at first sexual maturity; and (e) the fecundity
Summary
Fish have developed reproductive strategies and traits that ensure the survival of the species under variable and often unfavourable conditions (Potts and Wootton, 1984). As a typical opportunistic species (Cury and Fontana, 1988), it has invaded the northern Aegean Sea waters over the last twenty years mainly due to climatic changes (Bethoux and Gentili, 1999). This is the case in the Adriatic Sea (Kacic, 1984). An adaptation of the species to the local environmental conditions should not be excluded (Cury and Fontana, 1988)
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