Early developmental stages of fish are particularly sensitive to water pollution. Heavy metals may affect various developmental processes during the embryonic period, which results in a reduction of offspring quantity and quality. Waterborne metals may accumulate in the gonads of spawners and adversely affect gamete production and viability, or exert direct toxic influence upon developing embryos. The egg shell does not fully protect the embryo against metal penetration, particularly during the swelling phase; thus, metals may accumulate in the egg. The results depend on metal concentration and range from developmental disturbances to death of the embryo. Metals disturb various processes of fish embryonic development and affect the development rate. Early stages just after fertilization are particularly sensitive to metal intoxication, when most disturbances and the highest embryonic mortality occur. Waterborne metals also promote developmental anomalies during organogenesis, including body malformations. Heavy metals often induce a delay in the hatching process, premature hatching, deformations and death of newly hatched larvae. All these disturbances result in reduced numbers and poor quality of the larvae, which show small body size, high frequency of malformations and reduced viability.

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Rainbow trout, Salmo gairdneri, were fed pelleted food ad libitum for 35 and 50 days. Lipid deposits were determined in the viscera, liver and muscle (epaxial and hypaxial). Most of the lipid accumulated in the viscera, but the lipid content of liver and epaxial muscle also increased. Hypaxial muscle lipid content remained the same throughout the feeding period. Upon starving the fish for 27 and 48 days following 50 days of feeding, visceral lipid contributed most to energy metabolism among the depots investigated. Muscle also contributed a considerable share while the absolute amount derived from the liver was much smaller.Patterns of fatty acid mobilization during starvation were also investigated. Saturated acids were preferentially mobilized from the viscera, resulting in a rise in the percentage of monoenes and polyunsaturates. In liver, the percentage of saturates remained relatively constant whereas the percentage of monoenes declined and polyunsaturates increased. In muscle, a substantial increase in saturates was caused by a decline in monoenes; polyunsaturate content remained constant. As a result of these shifts in relative fatty acid composition the U/S (unsaturates to saturates) ratio rose in viscera and liver and decreased in muscle. The UI (unsaturation index) responded in essentially the same way. Possible explanations for preferential fatty acid utilization are discussed in terms of energetics and structural relationships.

The main objective of the research was to learn whether selected physiological responses could be used as symptoms of forthcoming reproductive impairment in fishes subjected to acid stress. Electrolyte balance (Na+, Cl-) in blood and muscle, plasma osmotic pressure, internal water balance, blood glucose and liver glycogen were the most important parameters measured in rainbow trout, Safmo gairdneri, exposed for twothree weeks at six pH levels: 8.3, 7.7, 7.0, 6.2, 4.8, 4.2. In general, plasma and muscle Na+/Cll and plasma osmotic pressure declined sharply at higher acidities while energy mobilization responded in the opposite fashion.The data were interpreted in terms of zones of tolerance and resistance. The zone of tolerance lies between pH 9.0 and 5.0, while the zone of resistance extends beyond pH 5.0. Complete regulation of physiological parameters occurred between the highest measured pH, 8.3, and 6.0. The limits of partial regulation and loss of regulation were tentatively set between pH 6.0 and 5.0 for the former and beyond 5.0 for the latter. Environmental and genetic factors are known to shift these limits.Reproductive stress occupies a zone between pH 5.5 and 6.5, according to laboratory and field observations on several species. The zone of reproductive stress overlaps the limits of complete and partial regulation. The physiological parameters therefore, would not be expected to exhibit consistently recognizable and dependable changes that would be useful to forecast reproductive failure. Severe acid stress could be diagnosed with the symptoms, however.A field test of the findings was provided by blood and tissue samples of white suckers, Catostomus commersoni, from an acidified (pH 5.2) and an unacidified (pH 7.2) lake in the Adirondack Mountains, Herkimer County, New York. Changes in electrolytes and glucose-glycogen, predicted from the laboratory experiments, were noticed in fish from the acidified lake, although the changes were not striking. These fish may have been in a physiological state of partial regulation within the zone of tolerance.

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The effects of 3 h exposure to 96hLC50 of cadmium (4.5 mg dm )3 ) on oxygen consumption rate, and hematological parameters (RBC, WBC, erythrocyte and leukocyte pattern) of juvenile tench were evaluated. Oxygen consumption significantly decreased beginning from 24 h postexposure, and remained reduced until the end of the experiment (96 h postexposure). RBC gradually increased, together with the percentage of juvenile cells in circulation. On the other hand, cadmium induced damage to the red cells -the share of cellular anomalies significantly increased with time postexposure. They included abnormal cell shape, vacuolization, swelling, chromatin disintegration in the nucleus, and nucleus indentation. The exposed fish showed a gradual and significant decrease in WBC without a shift of lymphocyte/neutrophil proportion. No significant changes in thrombocyte count occurred. The results show that short-term exposure to cadmium reduced fish energetic metabolism, and suppressed immune abilities. The symptoms gradually developed after the end of exposure, and no recovery took place until 96 h.

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Studies of carp fry, Cyprinus carpio, showed that temperature elevation within the range of 18-26" C increases the mortality caused by lowering the pH of water. It was found that 26-h acclimation in acidic water (mean pH 4.22) prolongs the survival of fish in water at pH 4.02420. Carp fry obtained less oxygen in water at pH 4.0, as compared to pH 7.0. The differences-though insignificant-pointed to an adverse effect of acidification on the respiratory processes.