A. P. Mansuri

Effects of chromium(VI) on some ion-dependent ATPases in gills, kidney and intestine of a coastal teleost Periophthalmus dipes.

The coastal teleost species, Periophthalmus dipes, commonly known as the mudskipper, was exposed to three sublethal concentrations (5, 10 and 15 mg/l) of potassium chromate for three exposure durations (2, 4 and 6 days). The study compares the dose- and duration-dependent effects of Cr(VI), as potassium chromate, on the ATPase systems in various organs of this fish species. In this study, effects of Cr(VI) stress on total ATPase, (Na+,K+)-ATPase, (Ca+2)-ATPase, (Mg+2)-ATPase, (Ca+2, HCO3-)-ATPase and (Mg+2,HCO3-)-ATPase in gills, kidney and intestine were estimated. A general dose- and duration-dependent inhibitory trend was observed. However, it is evident that exposure duration is more important then dose in the inhibition of the activity of the enzymes. At some concentrations, initial stimulation of the activity of some enzymes were also noticed. However, maximum inhibition was observed in higher Cr(VI) concentrations exposed for the longest time. It is possible that this inhibition of the ATPases by Cr(VI) blocked the active transport system of the gill epithelial as well as chloride cells, glomerular and epithelial cells of the tubules and thus altered the osmoregulatory mechanism of the fish. It appears that this heavy metal ion alters the membrane permeability of the intestinal epithelial cells and other layer of cells by altering the activity of ATPases, resulting in a breakdown of the active transport mechanism needed for the absorption of nutrients, ions and metabolites.

Mercuric chloride-induced inhibition of different ATPases in the intestine of mudskipper, Boleophthalmus dentatus

This paper deals with the toxicity of mercuric chloride to different ATPases in the intestine of mudskipper (Boleophthalmus dentatus). Mudskippers were exposed to four sublethal concentrations of mercuric chloride for three durations. The specific activities of Na+, K(+)-ATPase, Ca(2+)-ATPase, Mg(2+)-ATPase, Ca2+, HCO3(-)-ATPase, and Mg2+, HCO3(-)-ATPase were estimated. There was linear inhibition of all the enzymes with increasing mercuric chloride concentration as well as exposure duration. The Na+,K(+)-ATPase was found to be the enzyme most affected, followed by other ion-dependent ATPases. Inhibition of all the enzymes indicates severe damage to the intestinal cells, resulting in a blockage of the transport of substances across the membrane.

Growth of Pectoral Muscle Fibres in Relation To Somatic Growth in Some Marine Fishes

In the present communication, growth dynamics of pectoral muscle fibres of four marine fishes are described in relation to their somatic growth and the results are comparedwith our earlier findings on Caranx malabaricus. Over the entire investigated size range, the growth of red fibres was principally by hyperplasia. In pink fibres, cessation of hyperplasia was found in three of the five investigated species, whereafter further growth was only by hypertrophy of existing fibres. In white fibres, hypertrophy is a more important mode of growth than in other muscle fibre types. This was apparent from a smaller fish size at which addition of new fibres ceased or from a steeper slope of the relationship between muscle fibre diameter and fish fork length for most of the investigated fishes. However, Boleophthalmus dentatus seems to be an exception. The observed fibre growth dynamics of these fishes are similar to those of myotomal and caudal muscles.

Growth dynamics of the red, pink and white fibres in the caudal fin muscle in relation to the somatic growth in few marine fish

The growth patterns of red, pink and white fibres in the caudal fin muscle of five marine fishes, in relation to their somatic growth rate, are discussed in the present article. The results show that the fast growing species showed continuous recruitment of small new fibres and the slow growing species showed an increase in the fibre diameter of existing fibres instead of recruitment of new fibres. While the moderate growing species possessed both the processes equally. The results indicate that the growth dynamics of all the fibre types are related to the same found in the myotomal muscle and paralleled with the somatic growth rate. Studying the relationship between cessation fork length (x) and ultimate size (y) by regression equation of y = —0.2557 + 1.90x, it is revealed that when the fish acquires 53% of its ultimate size, the recruitment of small fibres stops and further growth occurs by an increase in the diameter to reach the ultimate size of the species.