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Factors involved in the determination of the blood sugar level of L. capensis have been studied. The stress of capture and transportation produces a marked increase in the blood sugar concentration. The relationship between blood sugar concentration and oxygen saturation of water and between blood sugar concentration and ammonium ion concentration was also investigated. Increases in ammonium ion concentration and decreases in oxygen saturation of water produce increases in the blood sugar concentration. The results are discussed in relation to the phenomenon of ‘asphyxiation hyper-glycemia’.

Sarotherodon mossambicus, Cyprinus carpio 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 carpio exhibited the greater ability to survive at these temperatures. Sarotherodon mossambicus experienced osmoregulatory collapse at 15° C which also occurred in trout at 25° C. This was associated with acid-base malfunction in the trout.

Heparin injection B.P., containing 0·5% phenol as preservative, disodium ethylenediamine tetra-acetate (EDTA), trisodium citrate (TSC) and ammonium potassium oxalate (APO) were compared as anticoagulants for routine haematological investigations in Cyprinus carpio and Sarotherodon mossambicus. The acidic nature and haemolytic effects of EDTA and APO render them unsuitable for use with fish blood. TSC was required in higher concentrations (than heparin) for effective anticoagulation and this was undesirable for the determination of blood pH and pCO2 and certain other parameters. Several important interspecies differences in the reactions towards the anticoagulants are also reported. In general, heparin proved to be the anticoagulant of choice, although unsuitable for some assays.

The plasma proteins of L. umbratus and L. capensis have been investigated by means of cellulose-acetate and polyacrylamide gel electrophoresis. Characteristic patterns were obtained for each specie although variations occur within a certain basic framework. Certain fractions were further isolated and approximate average molecular weights were found to vary between 55 000 and above 120 000 and isoelectric points between 5.78 and 4.2. Certain fractions were found to exist in dimeric form. It is concluded that the application of the human nomenclature to fish plasma protein fractions is of dubious value and that the fish fractions can only be classified after thorough biochemical investigation.

Various haematological values of wild yellowfish (Barbus holubi), carp (Cyprinus carpio) and two species of mudfish (Labeo umbratus and Labeo capensis) were examined on a seasonal basis from May 1975-April 1976, obtained from three different localities. Haematological values of fish of different length groups (from all four species) were studied at one locality during winter only. (June 1976-August 1976). Seasonal variations were observed in all of the parameters studied but no sexual differences were found and no significant changes in the haematology could be related to breeding season. Wide individual variations were evident in fish of different length groups and no correlation existed between fish length (and mass) and haematological values.

Interspecies haematological differences to MS 222 and neutralized MS 222 anaesthesia were investigated in Sarotherodon mossambicus, Cyprinus carpio and Salmo gairdneri 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 effects of MS 222 and neutralized MS 222 anaesthesia on haemoglobin electrophoresis, erythrocyte adenosine triphosphate (ATP) levels and corpuscular fragility curves were studied in Cyprinus carpio, Sarotherodon mossambicus and Salmo gairdneri. Haemoglobin electrophoresis showed no significant intra-species differences in the percentage composition of the various fractions for any concentration of MS 222 and neutralized MS 222 used. Significant interspecies differences were, however, still observed. ATP levels showed intra and interspecies differences ascribed to the response of the fish species to MS 222-induced stress and not to actual changes in erythrocyte ATP concentrations. Differences were also observed in corpuscular fragility curves for all three species when using MS 222 or neutralized MS 222 compared to curves obtained without the use of the anaesthetic, but the mechanisms involved are not clear.

The ranges and mean values for several blood parameters of adult specimens of Hypophthalmichthys molitrix were determined in order to establish a standard haematological profile for future investigations. Several significant correlations were established, the most important being between haematocrit, haemoglobin and erythrocyte counts. The data are discussed in relation to the general biology of this species.

The surface area of two closely related mudfish species have been determined by coating the animals with masking tape. The results indicate that Labeo capensis specimens above 95 g body weight have a larger surface area than corresponding L. umbratus animals. The same is true for the fin surface area above 50 g body weight. Below these weights L. umbratus specimens have higher surface areas. The body surface area of L. capensis is always lower than that of L. umbratus in the range studied.

Various parameters of the blood physiology of five South African species of fish have been investigated. The results show that plasma and serum samples differ in electrophoretic pattern, and also in the number of fractions and the protein concentration of these fractions. Red blood cell measurements, hemoglobin concentrations and blood glucose concentrations differ from fish to fish, and appear to be species specific. The values reported here are comparable with similar results obtained by other workers.

The haemoglobins of both L. umbratus and L. capensis separated into four components on polyacrylamide electrophoresis. The isoelectric points of these fractions were found to be 9.35, 6.89, 6.63 and 6.40. Organic nucleotide triphosphate concentration in the blood of L. capensis was found to be 56.72 ± 18.01 mg% and 58.72 ± 17.9 mg% in the case of L. umbratus. It is not possible to distinguish between L. umbratus and L. capensis purely on the basis of the haemoglobin electropherogram.

L. umbratus pituitary glands were partially separated by means of preparative polyacry-lamide electrophoresis and chromatography on DEAE-cellulose and Sephadex G-50. Eight fractions were obtained and it was found that fraction 1 contained potent adrenocorticotropic stimulating activity, with a molecular weight in the region of 6000. Fractions 3 and 4 contained potent gonadotropic and a lesser degree of exopthalmic producing activity, with molecular weights in the region of 14 000 to 20 000. Fraction 6 displayed pigeon-crop stimulating activity, with a molecular weight above 30 000. Fractions 7 and 8 displayed M.S.H. and vasopressinoxytocic activity respectively, with a molecular weight in the region of 5500–6500. Fractions 2 and 5 could not be identified. The fractions seemed to be glycoproteins and the results are discussed in relation to previous findings.

Electrophoresis of haemoglobin in single erythrocytes of Labeo umbratus and Labeo capensis showed that haemoglobin behaved in three distinct ways in both species. The majority of cells contained haemoglobin which moved as a broad band towards the anode. In a few cells haemoglobin moved towards both the anode and the cathode and in even fewer cells, haemoglobin moved as a sharp band to either the cathode or anode. These results are discussed in relation to other observations.

The effects of the anaesthetic, MS-222, on the microhaematocrit value of freshwater fish have been examined. Blood containing MS-222 showed a higher haematocrit value than blood without the anaesthetic and haemolysis occurred in the former after a variable time depending on the concentration. The results are discussed in relation to previous findings.