G.J. Steyn

The fertilizing capacity of cryopreserved sharptooth catfish (Clarias gariepinus) sperm

Abstract Ova of one female were inseminated with cryopreserved and fresh milt. Cryopreserved milt was stored in liquid nitrogen for 14 days and 16 months. The insemination ratio was 0.3 ml milt 20 ml (±7600) ova. Cryopreserved and fresh milt were equally effective during the hatching trials. Fertilization with both fresh milt and milt cryopreserved for 14 days resulted in a maximum of 51% hatched ova. Milt which was preserved for 16 months caused the hatching of 41% ova.

The suitability of using cryopreservation of spermatozoa for the conservation of genetic diversity in African catfish (Clarias gariepinus)

Abstract 1. 1. The effect of cryopreservation of semen on expected Hardy-Weinberg proportions in the f1 progeny of selected breeding pairs was evaluated. 2. 2. Four different African catfish breeding pairs were selected, each pair displaying different heterozygous alleles at the glucose-6-phosphate isomerase-1 or 2 loci. 3. 3. Equal volumes of ova from each female were artificially inseminated with cryopreserved or fresh semen obtained from males possessing corresponding genotypes. 4. 4. A comparison of growth rates between f1 groups of offspring produced from fresh and cryopreserved semen was made. 5. 5. The G-test for goodness of fit showed no significant differences from expected Hardy-Weinberg proportions for allele frequencies obtained in the f1 progeny. 6. 6. The application of cryopreservation for the conservation of genetic diversity is discussed.

Some physical properties of the semen from artificially induced sharptooth catfish (Clarias gariepinus)

Abstract 1. 1. A programme for the artificial induction of spermatogenesis and spermiation in Clarias gariepinus is presented. 2. 2. The physical properties of the semen were determined. 3. 3. Semen colour was white in all cases and mean values for the other physical properties were as follows: semen volume = 9.91 ml; spermatocrit = 27%; sperm count = 6.2 × 10 6 /mm 3 ; percentage live spermatozoa = 87% and total motility time = 118 sec.

The role of the blood-testis barrier in the chemical composition of the seminal plasma of the freshwater teleost Clarias gariepinus

Abstract 1. 1. The chemical composition of the seminal and blood plasma of the sharptooth catfish C. gariepinus were analysed simultaneously. Concentration differences existed for various components in the seminal and blood plasma. 2. 2. Differences found could mainly be attributed to the functioning of a blood-testis barrier. 3. 3. The possible reason for the difference in concentration between specific components in the seminal and blood plasma while others remained unchanged is further discussed.

Allozyme variation in domesticated African catfish (Clarias gariepinus) from The Netherlands

Abstract 1. 1. Gene products of 20 protein-coding loci of 50 African catfish individuals, imported from The Netherlands, were examined by horizontal starch-gel and vertical polyacrylamide gel electrophoresis. 2. 2. No polymorphism could be detected at any of the loci examined, except at the esterase protein-coding locus which was not examined by previous authors. 3. 3. The loss of genetic variation could be attributed to the combined effects of a small founder population, limited numbers of parents used to produce the next generation and/or accumulation of genetic drift. 4. 4. The results are compared to those obtained by other authors for African catfish population.

A new sperm diluent for the artificial insemination of rainbow trout (Salmo gairdneri)

Abstract Abnormalities were previously noted on spermatozoa tails of several rainbow trout strains raised in southern Africa (Steyn et al., 1987). The fertilizing ability of rainbow trout milt which contained abnormal spermatoza, was investigated. An optimum milt to egg insemination ratio was established and different sperm diluents were evaluated. The sperm diluent which gave the best results was a Borax-boric acid buffer diluent, and the composition thereof is given in this paper.

Notes on the induced reproduction and development of the tigerfish,Hydrocynus vittatus (Characidae), embryos and larvae

SynopsisIn South Africa, the distributional range of tigerfish,Hydrocynus vittatus, has diminished over the past fifty years mainly as a result of migration barriers and reduced river flow. A project to restock traditional tigerfish waters has been envisaged for many years but did not materialise due to an inability to spawn this species artificially. Several hormones were therefore tested for their potency to induce ovulation in this species. Gonadotropin releasing hormones (GnRh) were used in combination with dopamine receptor antagonists. Human chorionic gonadotropin (HCG) was administered in conjunction with catfish pituitary gonadotropin. Both sexes were successfully stripped and the eggs were inseminated artificially. Tigerfish eggs are small (0.65 mm diameter), demersal and slightly adhesive. Hatching occurs 22 h 30 min after insemination and free embryos are pelagic and display continuous vertical movement for a period of three days. Embryonic development was photographed until first feeding, 5 days after hatching. From these results as well as field observations, it is concluded that tigerfish spawns on a sandy substrate in the vicinity of aquatic vegetation.

Tolerance levels of redbreast tilapia, Tilapia rendalli (Boulenger, 1896) to natural suspended silt

Tilapia rendalli was exposed to various siltconcentrationsfor different exposure periods to determine LC50 andsublethalconcentration ranges. The extent of damaging effects, if any,ofsuspended silt on the exposed fish, were investigated by meansofscanning electron microscopy. The LC50 values rangedbetween21 to 24 g l™1 and 42–48 g l™1 for juveniles andadultsrespectively. The silt concentrations tolerated by the testfisheswere above those found in most natural waters. The resultstherefore support the hypothesis that suspended silt is lethaltofish at concentrations higher than those naturally observed insurface water. The observed mortalities can be attributed tothecombined physical effects of high silt concentrations andassociated reduction in dissolved oxygen levels. To preventfishmortalities and other impacts on biota, anthropogenicactivitiesthat affect the natural variation in suspended siltconcentrationsin surface water should be carefully monitored and, wherepossible,be restricted.

Effect of excreta, blood and vitellus contamination on fertilisation success of Oncorhynchus mykiss

Abstract Egg batches are often contaminated by broken eggs, blood, faeces or urine. This study was conducted to determine what effect these contaminants have on fertilisation success, and also to determine the best diluent to use for fertilisation. Fertilisation successes were only negatively influenced when egg batches were intentionally contaminated with broken eggs, while contamination with blood, faeces or urine showed decreases which were not critical. Ovarian fluid was the best diluent to use when egg batches were contaminated by blood, faeces or urine, but not when contaminated with broken eggs. If egg batches are contaminated with broken eggs, it is advisable to use a salt solution, for example borax. Salt diluents keep the globulin in solution, which prevents blockage of the micropyle. The other possibilities are to prevent any eggs being broken during the stripping process by using well-trained strippers, to use a good stripping technique and to ensure that the eggs are handled carefully during the fertilisation procedure.

The effect of cryopreservation and various cryodiluents on allozyme variation of glucose phosphate isomerase in the F1 progency of african catfish (clarias gariepinus)

Abstract 1. 1. African sharptooth catfish individuals, heterozygous for glucose phosphate isomerase (GPI-2), were selected as broodstock by using horizontal starch-gel electrophoresis. 2. 2. Ova of one heterozygous female were inseminated with cryopreserved and fresh milt from a corresponding male. 3. 3. Significant deviations from expected Hardy-Weinberg proportions occured for offspring obtained by using cryopreserved milt. 4. 4. Differences in genotypic variation seems to relate to different cryodiluents and the fertility thereof. 5. 5. Selection of breeding stock for aquacultural practices based on the above information is discussed.