327first sexual maturity at a highly variable age (6-12 years), and the ovarian maturation rates within an age group are dependent on growth and body size. After the first spawning, the majority of white sturgeon males and females exhibit annual and biennial reproductive cycles, respectively. The environmental seasonality (temperature and photoperiod) plays an important role in synchronization of gonadal development and spawning. Reproductive management. The efficient utilization of sturgeon broodstock for either breeding or caviar production requires optimal environment and special techniques for reproductive management. New generations of the broodstocks are usually selected from the "production fish", at the age 3-4 years. Fish are sexed (by the surgical examination of their gonads) and marked. Mature males are selected for spawning by their external appearance, while the females are sampled each winter starting from the age 6-7 years, to segregate postvitellogenic, midvitellogenic, and previtellogenic (or early vitellogenic) stages of the ovarian maturity. Ripe females and males are held in cool water, chilled or natural, for at least 2 months before spawning. The optimal stage of ovarian development for hormonally induced spawning is predicted by the rate of germinal vesicle migration and verified by standardized egg maturation bioassay. Spermiation and ovulation are induced by the common carp pituitary extracts or GnRH analogs. The best performance (practically 100 % ovulatorq. response, 90 % fertility, and 80 ' YO hatchability) was recently achieved by the administration of GnRH analog in combination with doparnine antagonist (pimozide or domperidone). Current studies. With thl: improvements in reproductive management and spawning performance of domestic broodstocks, several other studies are currently initiated that will encompass a broader spectrum of applied research including reproductive physiology, selective breeding, health management, and identification of genetic :sex and monosex culture.

Extended Abstracts: Environmental and husbandry factors in sturgeon culture resistance to stress and intoxication, a reaction could only occur only after the ontogenesis of certain interactions in the endocrine system (Trenkler et al., tihis issue). Indirect evidence of bPP involvement in hypothalamo-pituitw interactions in sturgeon fry was the melanophore reaction, which was connected with inhibition of melanocyte-stimulating hormone secretion. The exact mechanism of bPP action in sturgeons needs further investigation. ReferenceKovalenko R. I., Zagustina L A,, Stepanova N. A. On mechanisms of antigonadotropic action of pineal polypeptides. Vopr. Of Neuroendocrinol., N 24, Lmingrad State Univ., 1983, p. 46-52.

The development of commercial sturgeon (Acipenseridae) culture in the Islamic Republic of Iran is based on the following: a) appropriate selection of splzcies to be reared, b) supply of artificial feeds which meet the requirements of different age groups, c) establishment of a technological scheme with control of breeding and d) determination of optimum environmental conditions.Commercial sturgeon culture technology must be developed in several directions: marketable fish rearing in tanks, pools, ponds, closed systems, as well as using combined methods, i.e. stocking pools of various capacity with subsequent transfer into grow-out ponds. Newly weaned fry as well as tank-and-pond raised fish may be used as seeding stock. A flexible biotechnology of marketable fish production may be applied depending on breeding methods and feed quality.The 1995-1996 experimental work determined the Sefidrud Russian sturgeon as a possible culture species. Pool-reared fish with a mean mass of 0.6 g were adapted to artificial paste foods. Fingerlings were further reared on artificial feeds with a formula very close to an optimum nutrient level for sturgeons of various age groups.The results demonstrate that the Sefidrud Russian sturgeon fingerlings may be reared on artificial feeds. Plastic tanks (1-4 m3) were used and fingerlings were raised 180 days up to a mean mass of 120g (a maximum mass of 300 g) which indicated their high potentialities. A mean daily growth rate of the Sefidrud Russian sturgeon of differenit age groups varied from 1.59% to 0.56Y0, the daily weight gain was from 4.23 to 1.42%. It was noted that a mean daily increment was affected by stocking density, daily rations, oxygen content, feed quality and maintenance of feeding routine. Fish growth rate was not constant in terns of variations in length and mass: length varied from 6.9 to 17.30/, mass from 14.5 to 42%. Optimum stocking densities were determined at which minimum variability is recorded and weight ratio shifts towards large well-growing fish. As the stocking density increases from 2-3 to 7-8 kg/m the rate of weight gain decreases from 2.9 to 1.2%. In order to maintain weight gains as high as 2.5-4.5% the stocking density of fish with a mass of 10-150g must be within 2.5-5.2 kg/m2.The effect of daily rations on the rate of weight gain was ascertained. As fish gained in weight from 10 to 200g daily rations were reduced from 40 to 9% of fish mass. And the mean daily rate of weight gain decreased from 5.0 to 1.8%. Studying the feeding habits of sturgeon reared in outside ponds can improve culture success. Qualitative and quantitative stomach contents and fullness of beluga (Huso huso L.) and bester (Huso huso L., x Acipenser ruthenus hybrid) fingerlings, and two-year olds, were studied over the summer feeding season. At the same time observations were made of the development of benthos and plankton in the ponds. The basic food of beluga and bester fingerlings at the beginning of summer was composed of waterbugs, heteroptera (Sugara and Notonecta). These repre...