We investigated the feasibility of cryopreservation of zebrafish (Danio rerio) blastomeres and primordial germ cells (PGCs) by rapid freezing of dechorionated whole embryos at the blastula, gastrula and segmentation stages. Initially we examined the glass-forming properties and embryo toxicities of 5 cryoprotectants: methanol (MeOH), ethylene glycol (EG), dimethyl sulfoxide (DMSO), propylene glycol (PG), and 1,3-butylene glycol (1,3-BG). Embryos at the blastula and gastrula stages had high sensitivities to cryoprotectant toxicities and were fragile against mechanical damage. Thus the segmentation stage embryos, the PGCs of which were visualized by injecting green fluorescence protein-nos1 3'UTR mRNA, were frozen using solutions containing each cryoprotectant at 6 M (first trial) and 2 types of cryoprotectants at 3 M each (second trial). In the first trial, live PGCs were recovered from most of the embryos frozen with EG (about 2 cells/embryo); however, a few embryos had live PGCs when embryos were frozen with other cryoprotectants. In the second trial; a mixture of EG + PG better preserved the viability of PGCs in frozen embryos. Live PGCs were recovered from all embryos frozen with EG + PG (about 3 cells/embryo), and the survival rate of PGCs was estimated to be about 25% based on the number of live PGCs in fresh embryos (about 12 cells/embryo). The present study indicates that we can utilize rapid freezing of dechorionated whole embryos at the segmentation stage for the cryopreservation of PGCs.

The study determined the types of pesticide/herbicide pollutants in water, sediment and fish from the Kafue River. A preliminary investigation of the oxidative stress from these pesticides/herbicides was also assessed by measurement of catalase activity. Water, sediment and fish samples were collected upstream, midstream and downstream the Kafue river in Chingola, Kitwe, Kafue National Park and Kafue Town. Water, sediment and fish muscle were sampled and analysed for pesticides using Gas chromatography. For catalase activity fish liver samples only were examined. The pesticides/herbicides detected in all samples collectively included: Heptachlor, pp'-DDE, Cypermethrin, Chlordane, Toxaphene, Terbufos, Kelthane, Endosulfan, Dieldrin, pp'-DDD, pp'-DDT, Atrazine, Disulfoton, d-trans-Allethrin and Endrin. On the other hand, catalase activity was detected in all fish liver samples from all sites. Its levels increased significantly from Chingola upstream to sites down-stream with highest being in Kafue town. This study therefore, demonstrates that there is widespread contamination of the Kafue River with pesticides/herbicides. It also demonstrates that organochlorides are found throughout the river especially in fish samples. The spectrum of pesticides/herbicides was much wider in fish probably due to bioaccumulation. It was also observed that fish are subjected to oxidative stress as determined by catalase levels. The stress is more pronounced downstream where the catalase levels were significantly higher than Chingola. The observation that more pesticide varieties are also found downstream may suggest a likely causative effect of the pesticides on oxidative stress although this needs further investigation. This study further tentatively highlights the potential dangers of these agro-related substances to dependants of the Kafue River water body and the need to carry out risk assessments and thereafter institute corrective measures to help reduce contamination and adverse effects.

There were presented data on etiology, specific prophylaxis and treatment of the most widespread infectious diseases of fishes in the Republic of Belarus: aeromonosis, pseudomonosis, swim bladder inflammation (air bladder disease), viral branchionecrosis. For the preparation of highly efficient specific medical and veterinary preparations it was recommended during the outbreaks of fish diseases to allocate the local pathogens on the basis of which it was recommended to produce vaccines both for perinatal and immersion administration for their wide use both for commodity fishes and for different ages and categories