P. K. Roy

Ultrastructural changes in the respiratory lamellae of the catfish, Heteropneustes fossilis after sublethal exposure to malathion.

Transmission electron microscopy study of the gills of Heteropneustes fossilis, exposed to 4 mg/liter of malathion (1/3 of LC50) for 24, 48, 72, and 96 h showed significant changes in its ultrastructures. Exposure to the pesticide after 24 h caused a slightly disarrayed condition in the double layered epithelial structure. Lymphatic spaces became more apparent, and a few chloride cells appeared which protruded toward the peripheral margin of the secondary lamellae. Chloride cells were exposed to the exterior by an apical pit. Pinocytosis was observed with marginal folds (MF) originating from the pillar and epithelial cells. Some vascular constrictions were also seen in the capillaries with erythrocytes. After 48 h exposure, the outer epithelial cells were stretched into a thin boundary wall and lymphatic spaces were engorged with plasma exudate. Chloride cells transversed the whole epithelium of the lamella and came into direct contact with lymphoid space and exterior to epithelial lining. Basement membrane of the capillaries became thicker. After 72 h a distorted lamellar epithelium ruptured in a few places allowing many spheroid bodies and some chloride cells come out. Marginal folds of pillar cells migrated into vascular spaces. Basement membrane of capillaries became thicker and blood channels were constricted causing vascular stasis. No erythrocytes were visible. Blood channels were filled with leukocytes and amoebocytes. After 96 h exposure to malathion narrowing of lymphatic spaces, proliferation of epithelial cells and development of pinocytotic vesicles from marginal folds of pillar cell flanges were observed. Only marginal blood channels maintained normal configuration. Vascular stasis due to thickening of the basal lamina were still evident in centrally located blood channels filled with leukocytes. Vascular stasis would likely cause a decrease in respiratory efficiency. This study has revealed that the gills of H. fossilis were affected by a sublethal dose of malathion. The ultrastructural damages to the gills were observed as early as at 24 h exposure, but the most severe damage occurred at 72 h exposure. However, signs of gill structure regeneration were seen in malathion-exposed fish after 96 h.

Angiotensin-converting enzyme in organs of air-breathing fish

Angiotensin-converting enzyme (ACE) was measured in tissue homogenates from the African lungfish and six species of air-breathing teleosts (Heteropneustes fossilis, Clarias batrachus, Channa gachua, Anabas testudineus, Notopterus chitala, and Monopterus cuchia) using a standard spectrophotometric assay. In most species, the highest levels of ACE activity were found in the respiratory organs (gills and/or accessory respiratory organs). ACE was also found in heart and kidney tissues from most species and occasionally in liver. Converting enzyme was not found in skin or skeletal muscle from any species and only in blood from H. fossilis and brain from C. batrachus. Captopril, a potent inhibitor of mammalian ACE, inhibited enzymatic activity from all tissues except C. gachua heart and liver and A. testudineus heart. As fish make the transition from aquatic to aerial respiration the gill microcirculation is usually reduced in size and the accessory respiratory organs become elaborated and occupy a more central position in the vascular tree. The presence of ACE in accessory respiratory organs of air-breathing fish appears to greatly enhance the metabolic efficiency of this enzyme on circulating substrates.

Sublethal malathion induced changes in the ovary of an air-breathing fish, Heteropneustes fossilis: a histological study

This paper describes effects of a sublethal (1.2 mg 1−1) organophosphate, malathion, on the ovary of an air breathing catfish, Heteropneustes fossilis. The study focuses on microscopic changes that occur on ovigerous lamellae, oocytes at different stages of development and the nucleus of the immature oocyte. Also, change in estrogen levels in blood serum is investigated. Clumping of cytoplasm appears after 24 h of exposure to malathion. Clumping intensified after 48 h. Degeneration in the follicular cells was also observed. After 72 h exposure the number of nucleoli increased, nuclear materials shrunk, oocytes became adhered. With 96 h of exposure, nuclear materials of all the oocytes shrunk to a smaller clump. The oocytes fused together, and follicular epithelium became loose and ruptured. A few atretic oocytes were visible. Radioimmunoassay of the estrogen level in blood serum after 72 h of exposure of malathion showed a reduction in the level. This study showed that the histopathological condition of the gonad is reflected in malfunctioning of the endocrine system and hormonal disbalance.

Effects of Diazinon on bluegill sunfish, Lepomis macrochirus, gills: scanning electron microscope observations

Gills of bluegill sunfish, Lepomis macrochirus, exhibited varied degrees of structural damage following a 24-h exposure to sublethal concentrations (15 µg/1, 30 µg/l, 45 4g/1, 60 µg/1 and 75 µg/1) of Diazinon [O,O-diethyl-O- (2-isopropyl-6-methyl-4 pyrimidinyl ester or phosphorothioate]. Exposure to 15 µg/1 and 30 µg/1 resulted in exocytosis of some material to the cell surface and perforations of the microridges. At higher doses (above 45 µg/1), the extrusion was reduced and the cells were swollen. Compared to control values, the thickness of the microridge on the gill arch and on the gill filament generally increased with exposure to Diazinon. Also, the distance between microridges decreased with increased exposure concentrations. At 60.tg/1, gill arch microridges fused and some ridges of gill filaments disappeared. At 75 µg/1 exposure, epithelial cells of the gill arch became obscured with severe cellular extrusions and the lamellar surfaces swelled. The mucus extrusion, lamellar swelling and reduced microridges may be related to a defence mechanism which reduces the water surface around the gill and increases the barrier distance for diffusion of toxicants from outside to the blood capillaries. Although this mechanism protects the fish from toxicants, it also reduces the oxygen supply which leads to suffocation of the fish.

Variation in Toxicity of Malathion to Air and Water-Breathing Teleosts

Malathion belongs to the widely used group of organophosphorus insecticides. In the mid 1960s there was a shift in insecticide use from the organochlorines to the relatively less stable and rapidly biodegradable organophosphate and carbamate classes (Murphy 1980). Many chemicals of these classes have become environmental contaminants in India (Verma et al. 1979). In India Malathion is one of the insecticides largely used to control mosquitoes and other insects. Its wide use provides many occassions for its entry into aquatic environments. The presence of this chemical in the aquatic environment would adversely affect many non-target species such as fish.

Morphometrics of the respiratory organs of a freshwater major carp,cirrhinus mrigala in relation to body weight

The surface area of the gills of a freshwater major carp,Cirrhinus mrigala was measured in specimens of body weight range from 5.0 to 1821.0 g and the data were analysed with respect to body weight using logarithmic transformations (log Y=log a+b · log W). The slope of the regression line for total gill area was 0.8158 and for the 1st, 2nd, 3rd and 4th gill arches were 0.8013, 0.8068, 0.8157 and 0.8457 respectively. The slope value for secondary lamellae is 0.3151, whereas the intercept value for the same parameter comes to 178,887.98. The slope for average bilateral surface area of a secondary lamella is 0.5007. These results indicated differences in growth patterns for the dimensions of different gills. The growth related decrease in number of secondary lamellae per mm filament length (b= −0.1287) and gill area/g body weight (b = −0.1842) together with evidence from oxygen uptake suggests that larger fishes consume less energy per unit body weight than the smaller ones. The percentage shrinkage due to fixation in Bouin’s fluid in filament length and average bilateral surface area were 3.05±0.47% and 15.19 ±3.48% respectively.