engleski

Annual oscillation of ovarian morphology in European pilchard (Sardina pilchardus Walbaum) in the northern Adriatic Sea

Anual oscilation of ovarian morphology in European pilchards (Sardina pilchardus walbaum) caught in the period from july 2001 to june 2002 in the region of the Northern Adriatic (Croatia) was studied. Fifty females were taken in the middle of each month and determining body mass they were dissected, ovaries extracted and weighed, and the centre of each ovary was sampled for histologic analysis.Samples were fixed in the Bouin's solution, mounted in paraffine and cut into 6 µ ; m thick slices wich were stained with hematoxylin and eosin (HE) and by the Periodic-acid Shiff method (PAS). During oogenesis the oocytes passed through four developmental phases: peri-nucleolus stage (phase I), yolk vesicle stage (phase II), yolk stage (phase III) and mature stage (phase IV). Oocytes in the phase I were present during all months, forming more than 40% of all oocytes. Their percentage increased from May to August (P<0.05) and was the highest in the August (84%). Percentage of oocites in the phase IV was on increase from October to April (P<0.05) and was the highest in the November (36.3%). An increase in percentage of phases II and III of oogenesis was noticed in September and remained at an almost equal level until May. The developmental cycle of oocytes began in September and October, coinciding with an increase of the ovarian mass which attained its maximum level in October, remaining et an almost equal level until April. During this period the mass of ovaries reached more than 4% of body mass, and GSI (gonadosomatic index) was significant different (P<0.05) from other months.

Sardina pilchardus Walbaum ; ovaries ; oocyte stages ; Adriatic sea ; Croatia

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