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Sand and common goby specimens were collected from the costal waters in the vicinity of Sopot and Chałupy (Gulf of Gdańsk) from August to October. The relationship between the food consumed and the fish condition was investigated for both species using the Fulton and Clark factors, HSI, feeding intensity, and the index of relative importance. The results indicated that the mean values of the common goby condition factors (20 – 29 mm) were higher in September, the last month of reproduction. The sand gobies (30 – 39 mm) were characterized by lower condition factor values in September, one month after spawning. It was concluded that there is a direct link between diet composition and goby condition during spawning and in the months following it.
In the Polish costal zone of the Baltic Sea two similar looking gobies – sand goby and common goby occur. In quantitative investigation both species are often taken as an one, because of difficulties in distinguish them. There are a few methods to differentiate sand goby and common goby - body pigmentation, shape of head and pigmentation of a spleen (Ławacz 1965). During the investigation it was proofed that compared species differ from each other also in biological characteristic. In the Gulf of Gdańsk spawning-season starts for sand goby in March and ends in September, for common goby it lasts from March to August. They have different sex ratio, but they have similar range of a HSI and GSI coefficients. Those differences and similarities are important for future investigations because they show that sand goby and common goby should be separated in studies
The reproduction aspect of the biology of Pomatoschistus minutus was investigated on fish collected in the Gulf of Gdańsk from March to October 2002. The study zone was from the shore to a depth of about 1 m. The sand goby is common in the investigated area from July to October, but it migrates to deeper water in the colder months. The highest numbers of individuals were observed in September. The spawning season of the sand goby in the Gulf of Gdańsk is from April to August. It is so long because this species is batch spawner. The study confirmed a dependence between the HSI and GSI indexes as well as the dependence between relative fecundity and fish length.
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