Morphometric characteristic of gonadal cycle of mussel Dreissena polymorpha (Pallas, 1771)

Istraživanje školjkaša Dreissena polymorpha provedeno je na hidroakumulacijskom jezeru Dubrava tijekom jedne godine. Razvojni stadiji gonada određeni su histološkim tehnikama, a volumen gonada, utrobne vreće, probavne žlijezde, probavila i ostalih tkiva izračunat je pomoću računalnog programa LUCIA G 4.81, kao i pripadajući indeksi. Omjer spolova bio je približno 1:1. Gametogeneza započinje tijekom jeseni, a razvoj gameta ubrzava se u proljeće. Do mriještenja dolazi tijekom kasnog proljeća i ljeta. Većina jedinki reproduktivni ciklus završava u srpnju. Najviša prosječna vrijednost indeksa spolne zrelosti utvrđena je u srpnju, a najniža u kolovozu. Najviše prosječne vrijednosti gonadnog volumena i gonadnog indeksa zabilježene su kod mužjaka u lipnju, a kod ženki u travnju. Najniže vrijednosti zabilježene su u kolovozu. U sinkronitetu gonadnog ciklusa između spolova postoje razlike tijekom faze mirovanja i gametogeneze, dok su za vrijeme mriještenja mužjaci i ženke sinkronizirani. Vrijednosti indeksa probavne žlijezde, probavila i ostalih tkiva utrobne vreće najviši su kad su vrijednosti gonadnog volumena i indeksa najniže. Utvrđena je i prisutnost metilja, što negativno djeluje na razvoj gonada.The research of mussel Dreissena polymorpha was conducted during one year at hydroelectric power plant reservoir Dubrava. Developmental stages of gonads were determined by histological techniques. Gonad volume, volume of the visceral sac, digestive gland, digestive tract and volume of other tissues of visceral mass were calculated using computer program LUCIA G 4.81, as well as the corresponding indices. The gender ratio was approximately 1:1. Gametogenesis begins in autumn. The spawning occurs during late spring and summer. Most individual complete the reproductive cycle in July. The highest average value of sexual maturity index were determinated in July, and lowest in August. The highest value of gonad volume and gonad index observed in males were in June, and in females in April. The lowest values were recorded in August. Differences between two sexes ocurred in the timing of the resting phase and gametogenesis, while during the spawning males and females were synchronized. The digestive gland index, digestive tract index and other tissues of visceral sac index were the highest when the value of volume and gonad index were the lowest. The presence of endoparasites trematoda was identified, which negatively affects the development of the gonads