No abstract

Juvenile paddlefish (Polyodon spathula) hatched in 1988 have been cultivated in ponds up to sexual maturity (age 11+) in Moldavia, located in central European Plain with an altitude ranging from 429.5 m to 147 m. The average annual air temperature is 9.5–10 °C and the growing season for pond fish is 180 to 210 days. The first summer the fish were reared under either mono‐ or polyculture conditions starting at an initial stocking density of 10000 and 5000 fish ha–1. By the autumn the individual weights were 72 and 139 g and the survival rate 48 and 63%, respectively. In subsequent years the paddlefish were associated in ponds with various sturgeon species. A polyculture experiment associating the sturgeon, Acipenser baeri (density 4300 ind. ha–1) and paddlefish (density of 8300 ind. ha–1) yielded respectively 59% survival and 432 kg ha–1 productivity for Polyodon and 77% survival and 174 kg ha–1 productivity for A. baeri. By the third year (2+) the paddlefish reached average weight of 1.5–2.5 kg and their final survival and productivity values were 50–70% and 150–463 kg ha–1, respectively. Males (6–7 kg ) matured at the age of 5+– 6+. Females reached sub‐final stage IV at the age of 11+ (30%) or 12+ (70%) and a weight of 10–16 kg with spawning and production of viable fry. Caviar was made from the roe of these females. In 1+–3+ aged fish, the proportion of flesh and skin was stable at 54–57% while the proportion of head decreased from 44% at 0+ to 26% at 3+.

Aim. The study was aimed at determining the cytological changes, related to the germinal vesicle (GV) of porcine oocyte during the follicular maturation. Methods. The ovaries were classifi ed according to the estrous cycle phase, judging by the status of yellow bodies and follicles. The oocytes were isolated from each animal using dominating and atresiated follicles separately. The oocytes were used to prepare whole mounts by a specially designed express-method, which is thermal fi xation (about 95 °С) and their further transfer into the medium for clarifi cation. The whole procedure of preparing the mount from one oocyte or their group lasted for about 10 min. The microscopic studies were conducted using the phase contrast. A total of 831 oocytes were studied. Results. It was established that sow oocytes had eccentric location of GV which may be found in oocytes from early antral follicles. This condition is kept until the beginning of meiosis restoration and GV destruction. The nucleolus is also located eccentrically. Another relevant cytological change was gradual condensation of chromatin around the nucleolus, starting from separate clots on its surface and further formation of circular structures. Conclusions. Contrary to laboratory rodents, GV in porcine oocytes has eccentric localization, which is set even in early antral follicles and remains until the beginning of meiosis restoration. The process of chromatin transformation was found to be its gradual condensation around the nucleolus which may be defi ned as a nucleolus complex.

A brief survey of the Russian literature of the production of live preys for feeding young sturgeons is presented. These preys are plankton organisms (Moina, Daphnia, Artemia), chironomids and oligochaets cultured in large scales mostly in state hatcheries to produce sturgeon juveniles for stocking. Thus those culture systems operate only for a short period of time. In general, an innoculum of broodstock material is introduced into the tank or the pond in which the preys are cultivated. Various feeds and fertilisers are distributed. Daily production is 10 g/m2 for chironomids and 55 g/m2 for oligochaets. For daphnia, under optimum condition of temperature and water quality the production is 20 to 35 g/m3 for the whole season. Such productions are high but the systems operate only during few months corresponding to the short rearing period of sturgeon, at least in the case of stocking. In indoor condition the plankton is distributed to the sturgeons in the rearing tank. One way is to keep constant the plankton concentration (5 mg plankton wet weight per 1 m3 of water). Associations of preys are also given; for instance zooplankton and oligochaets distributed in % of the fish biomass: 20% the first 20 days and 15% from days 30 to 40.