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SUMMARY: The histological characteristics of wild and cultured Mediterranean amberjack gonads were studied during the first four years of their life cycle. No differences were found in the gonad development of both wild and captive males and females during the first and second year. In the third year, wild females showed more advanced oocyte development than captive females. In the fourth year, vitellogenic oocytes were noted for captive females. Fertilised eggs were obtained after a HCG hormone treatment of four-to nine-year old wild specimens. A smaller quantity of mature and fertilised eggs was also obtained through the spawning of hormone-treated four-year old captive broodstock specimens. Eggs in the stage of gastrulation died within eight hours following fertilisation.

The present paper describes sex reversal in dusky grouper, Epinephelus marginatus (Lowe). Over a 4-month feeding period, 5 mg kg -1 of the male hormone 17-α methyltestosterone was combined with frozen fish as feed. After 2.5 months of treatment, the gonads of all six fish treated in the experiment presented tissues with oocytes and spermatogonia, and after 3 months, there were only a few remnants of oogonial tissue left in the gonads. All fish in the experiment gave sperm of varying quality after 4 months of the trial. The quantity of the hormone administered to the fish over these 4 months was 89-113 mg kg -1 . Spermatozoid motility varied from 95% to 40%, and lasted for about one hour in sea water. Using the combined sperm of three males, fertilization ranged from 50% to 95%. Fertilized eggs and hatched larvae continued to develop normally.

Short CommunicationAge, growth, mortality and sex ratio of sand smelt, Atherina boyeri Risso, 1810 (Pisces: Atherinidae) in the estuary of the Mala Neretva River (middle-eastern Adriatic, Croatia) Summary The present study investigated the age, growth, mortality and morphometry of the sand smelt, Atherina boyeri, in the Mala Neretva River estuary (mid-eastern Adriatic Sea). The study of scale annuli showed that the population is up to 4 years of age. However, most sand smelt are in their first and second year; the numbers of older individuals are very low because they migrate upstream and are heavily fished. The von Bertalanffy parameters for the total sample of sand smelt were found to be L ¥ ¼ 13.5 cm, K ¼ 0.37 year )1 and t 0 ¼ )0.97. Overall total mortality was estimated at 1.81 year )1 , natural mortality was 0.90 year )1 and fishing mortality was 0.91 year )1 .

SUMMARY: The embryonic and early larval development of the laboratory-reared goldblotch grouper, Epinephelus costae (Steindachner, 1878), are described and illustrated. The eggs, with a mean diameter of 926±19 µm and a range from 890-950 µm, were spherical and transparent with transparent chorion. Embryonic development lasted 24 hours at 25.5°C. Newlyhatched larvae were 1.762±0.047 mm in length. Absorption of the yolk sac was complete after the third day, when larvae reached 2.95±0.231 mm in total length. The mouth opened 60 hours after hatching, and was in function after 80 hours, with an opening diameter ranging from 280-320 µm. Larvae had two fields of intensive pigmentation, one above the intestine, and the other between the anus and the end of the notochord.