University of Nairobi

The kidneys of four freshwater teleost fish Oreochromis niloticus, Micropterus salmoides, Cyprinus carpio and Clarias mossambicus and one marine teleost, Chanos chanos, representing Perciformes (O. niloticus and M. salmoides) Ostariophysi (C. carpio, and C. mossambicus) and Salmoniformes (C. chanos) were studied for qualitative and quantitative characteristics using materials fixed in situ by perfusion via the bulbous arteriosus into the entire renal arterial system. The kidneys of O. niloticus, M. salmoides and C. carpio were partially fused and those of C. mossambicus and C. chanos were completely fused. Partial or complete venous portal systems were present in all the species except O. niloticus. The renal lobule was centered on the intralobular artery and duct and delimited by efferent veins. The nephron of the fishes consisted of a renal corpuscle, the neck, proximal 1, proximal 2 and distal segments and the collecting tubule-collecting duct system. These parts of the nephric tubule were distinguished on the basis of their staining reactions and histological and ultrastructural characteristics. Intrarenal heamopoietic tissue was absent in the Perciformes teleosts but was abundant in the Ostariophysi and Salmoniformes. Interrenal tissue in the head kidney was arranged in cords around branches of the posterior cardinal vein. Rodlet cells have been described in the proximal tubule of the blackbass

Acta Biologica Hungarica 45 1 111 121 HUNGARY

Ultrastructural studies were carried out on the nephron of a euryhaline teleost, Oreochromis niloticus. The nephron consisted of a renal corpuscle, neck segment, bisegmental proximal tubule and a distal tubule. Renal corpuscles displayed a trilaminate structure of fenestrated endothelium, triple layered basement membrane and a highly branched podocyte layer. Neck segments consisted of low cuboidal cells with apical cilia and few vacuoles. Proximal tubules were made up columnar cells with apical brush border. The initial part of the proximal tubule (PI) was characterized by a well developed endocytic apparatus which was absent in the next part (PII). Distal segments comprised of low columnar cells with scanty or no microvilli and an extensive system of basolateral membrane infoldings associated with mitochondria. These findings have been discussed in relation to renal function in fresh water euryhaline teleosts

Australasian Journal of Ecotoxicology 10 1 1 20

Exploitation of natural mineral deposits and subsequent re-deposition in aquatic environments at levels potentially harmful to biota necessitate regulation of environmental discharge of metals. Proper environmental regulation of metals requires adequate knowledge on the bioavailability and effects of metals on aquatic organisms. Moreover, the need to better understand biological effects of metals has given impetus for studies on the homeostatic physiology of metals because the root cause of toxicity is the breakdown of homeostasis. In this paper we review recent advances in the understanding of the environmental chemistry, toxicology, and physiological homeostasis of copper (Cu) in freshwater systems. Present water quality criteria do not adequately consider bioavailability and metal homeostasis. We show that consideration and incorporation of recent knowledge on bioavailability, homeostatic physiology, and acute and chronic toxic effects of Cu greatly improve the predictive precision of models, such as the Biotic Ligand Model, for ecological risk assessment and environmental regulation of Cu, and reduces the need for reliance on the Precautionary Principle. Furthermore, we highlight present gaps in knowledge of environmental physiology, homeostasis, and toxicology of Cu and suggest directions for future research

Canadian Journal of Fisheries and Aquatic Sciences 62 2 390 399 Ottawa, Canada: National Research Council of Canada.

Juvenile rainbow trout (Oncorhynchus mykiss) maintained on either low sodium chloride (LS (control), 1.4% NaCl) or high sodium chloride (HS, 11% NaCl) diet were exposed to 55 micro g.L-1 waterborne copper (Cu) for 28 days. Cu-exposed fish maintained on the LS diet exhibited 26% mortality, more than double (11%) that in fish maintained on the HS diet. Waterborne Cu exposure inhibited growth by 56% in fish maintained on the LS diet and by 35% in those maintained on the HS diet. Whole-body and tissue Na+ levels, measured 6 h after feeding, were increased by exposure to HS diet and reduced by waterborne Cu exposure. Exposure to elevated waterborne Cu increased whole-body and tissue Cu levels, whereas exposure to HS diet decreased these levels. Moreover, whole-body and tissue Cu concentrations were consistently lower in Cu-exposed fish maintained on HS diet relative to those maintained on LS diet. Plasma Na+ and Cl- levels were elevated by HS diet exposure and reduced by waterborne Cu exposure, whereas plasma Cu levels were decreased and increased by exposure to HS diet and waterborne Cu, respectively. These results demonstrate that elevated dietary NaCl modulates Na+ and Cl- homeostasis and reduces accumulation and toxicity of waterborne Cu.

Acute waterborne cadmium uptake in rainbow trout is reduced by dietary calcium carbonate

The effects of elevated dietary calcium (as CaCO3) and acute waterborne Cd exposure (50 μg/l) on whole body uptake, tissue uptake, and internal distribution of newly accumulated Cd, Ca2+, and Na + in juvenile rainbow trout were examined. Fish were fed with three diets (mg Ca2+/g food): 20 (control), 30 and 60 for 7 days before fluxes were measured with radiotracers. The highest dietary Ca2+ elevation reduced waterborne whole body Ca2+ uptake, but did not protect against inhibition of waterborne Ca2+ uptake by waterborne Cd. Both Ca2+-supplemented diets reduced newly accumulated Ca 2+ in the gills in relation to the control treatment, but did not prevent the Cd-inhibiting effect against accumulation of new Ca2+ in most compartments. Fish fed with Ca2+-supplemented diets showed markedly lower rates of whole body uptake and internalization (in some tissues) of waterborne Cd, illustrating that, while dietary Ca2+ supplementation did not protect against the impact of waterborne Cd on waterborne Ca2+ uptake, it did protect against the uptake of Cd. Waterborne Cd had no effect on Na+ fluxes, total Cl-, and in most body compartments, newly accumulated Na+ and total Na + were also not affected. Dietary supplementation with CaCO 3 had the same protective effect as demonstrated by dietary supplementation with CaCl2 in an earlier study. Thus, the reduction of waterborne Cd uptake and internalization by dietary Ca2+ was specifically due to Ca2+ and not to the anion. © 2004 Elsevier Inc. All rights reserved

A protective effect of dietary calcium against acute waterborne cadmium uptake in rainbow trout

The present study examined the interactions between elevated dietary calcium (as ionic Ca2+ in the form of CaCl2·2H 2O) and acute waterborne Cd exposure (50μg/l as CdNO3 for 3h) on whole body uptake and internal distribution of newly accumulated Cd, Ca2+, and Na+ in juvenile rainbow trout (Oncorhynchus mykiss). Fish were fed with three diets 20 (control), 30 and 60mg Ca 2+/g food: for 7 days before fluxes were measured with radiotracers over a 3h period. The two elevated Ca2+ diets reduced the whole body uptake of both Ca2+ and Cd by >50% and similarly reduced the internalization of both newly accumulated metals in most tissues, effects which reflect the shared branchial uptake route for Ca2+ and Cd. As the Ca2+ concentrations of the fluid phases of the stomach and intestinal contents were greatly elevated by the experimental diets, increased gastrointestinal Ca2+ uptake likely caused the down-regulation of the branchial Ca2+ (and Cd) uptake pathway. Waterborne Na + uptake and internal distribution were not affected. While plasma Ca2+ surged after the first two feedings of the 60mg Ca 2+/g diet, internal homeostasis was quickly restored. Total Ca 2+, Na+, and Cl- levels in tissues were not affected by diets. While dietary Ca2+ protected against waterborne Cd uptake, it did not protect against the relative inhibition of waterborne Ca2+ uptake caused by waterborne Cd. Acute exposure to 50μg/l Cd reduced the uptake and internalization of newly accumulated Ca2+ (but not Na+) by 70% or more, regardless of diet. Since elevated dietary Ca2+ reduces waterborne Cd uptake, fish eating a Ca 2+-rich invertebrate diet may be more protected against waterborne Cd toxicity in a field situation. © 2004 Elsevier B.V. All rights reserved