The chemical and physical characteristics of the semen of Cyprinus carpio and Oreochromis mossambicus were investigated on a comparative and seasonal basis. Results were obtained for the volume, colour and viscosity of the semen, the percentage live spermatozoa, sperm concentrations and the degree and the duration of sperm motility under different environmental conditions. All showed distinct interspecific and less conspicuous seasonal intraspecific differences. Values have also been determined for the organic and inorganic components and the pH and osmolality of the seminal fluid. Some inorganic and organic components indicated seasonal intraspecific differences while all the components, with the exception of sodium and galactose, indicated significant interspecific differences. These observations suggest significant interspecific differences in the testicular secretions of the two fish species which add to the basic physiological differences recorded for the spermatozoa of C. carpio and 0. mossambicus. The probable function of the carbohydrates, protein and enzymes present in the semen of these fish species are discussed. 263

Interspecies haematological differences to MS 222 and neutralized MS 222 anaesthesia were investigated in Surotherodon rnossurnbicus, Cyprinus curpio and Sulrno guirdneri acclimated under identical laboratory conditions. Anaesthesia with MS 222 resulted in a 'chemical stress' in all fish, as was evident from changes in the haematological profiles of the animals. Such species specific variations in the haematology persisted throughout the whole experiment protocol which employed different concentrations of the anaesthetic. The use of neutralized MS 222, whereby aquarium water quality remained unchanged, improved the haematological profile. Possible reasons for the interspecies differences observed are discussed.

The pH, pC0, and PO, values for diseased fish did not differ significantly from those values for healthy fish, but fish treated with terramycin showed a highly significant rise in pC0, with a corresponding fall in PO,. Haematocrit values, as well as haemoglobin and total plasma protein concentrations were significantly lower in diseased fish while treated fish showed a significant rise in total plasma protein. Glucose concentrations fell very significantly in diseased fish and showed a significant increase in treated fish.The plasma electrolytes, sodium, potassium and chloride, were significantly reduced in diseased fish and potassium levels also fell in treated fish. Diseased fish showed very significantly reduced erythrocyte counts. Of the three parameters MCV, MCH and MCHC, only the values for MCH in diseased fish differed significantly from those for healthy fish.

The uptake of benzocaine hydrochloride and neutralized benzocaine hydrochloride by the skin and the gills of Cyprinus carpio, Oreochromis mossambicus and Salmo gairdneri were studied. The differences observed can mainly be ascribed to degree of ionization and the lipid solubility of the anaesthetic.

Surotherodon mossambicus, Cyprinus curpio and Salmo gairdneri were acclimatized at temperatures of 15, 20 and 25'C in order to study physiological responses of blood to temperature fluctuations in the laboratory. Cyprinus curpio exhibited the greater ability to survive at these temperatures. Surotherodon mossumbicus experienced osmoregulatory collapse at 15" C which also occurred in trout at 25" C. This was associated with acid-base malfunction in the trout.