Early subcellular partitioning of cadmium in gill and liver of rainbow trout (Oncorhynchus mykiss) following low-to-near-lethal waterborne cadmium exposure

abstract: Non-essential metals such as cadmium (Cd) accumulated in animal cells are envisaged to partition into potentially metal-sensitive compartments when detoxification capacity is exceeded. An understanding of intracellular metal partitioning is therefore important in delineation of the toxicologically relevant metal fraction for accurate tissue residue-based assessment of toxicity. In the present study, the early intracellular Cd accumulation was studied to test the prediction that it conforms to the spillover model of metal toxicity. Juvenile rainbow trout (10–15 g) were exposed for 96 h to three doses of cadmium (5, 25 and 50 μg/l) and a control (nominal 0 μg/l Cd) in hard water followed by measurement of the changes in intracellular Cd concentrations in the gill and liver, and carcass calcium (Ca) levels. There were dose-dependent increases in Cd concentration in both organs but the accumulation pattern over time was linear in the liver and biphasic in the gill. The Cd accumulation was associated with carcass Ca loss after 48 h. Comparatively, the gill accumulated 2–4× more Cd than the liver and generally the subcellular compartments reflected the organ-level patterns of accumulation. For the gill the rank of Cd accumulation in subcellular fractions was: heat-stable proteins (HSP) > heat-labile proteins (HLP) > nuclei > microsomes–lysosomes (ML) ≥ mitochondria > resistant fraction while for the liver it was HSP > HLP > ML > mitochondria > nuclei > resistant fraction. Contrary to the spillover hypothesis there was no exposure concentration or internal accumulation at which Cd was not found in potentially metal-sensitive compartments. The proportion of Cd bound to the metabolically active pool (MAP) increased while that bound to the metabolically detoxified pool (MDP) decreased in gills of Cd-exposed fish but remained unchanged in the liver. Because the Cd concentration increased in all subcellular compartments while their contribution to the total increased, decreased or remained unchanged following Cd exposure, use of percentage data to infer spillover requires caution

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

Brown seaweed (AquaArom) supplementation increases food intake and improves growth, antioxidant status and resistance to temperature stress in Atlantic salmon, Salmo salar.

Seaweeds represent a vast resource that remains underutilized as an ingredient in aquafeeds. Here we probed the effect of addition of AquaArom, a seaweed meal derived from brown seaweeds (Laminaria sp., kelp), to fish feed on growth performance, antioxidant capacity and temperature responsiveness of mitochondrial respiration. A commercial salmonid feed was mixed with 0 (control), 3, 6 and 10% seaweed and fed to Atlantic salmon (Salmo salar) smolts for 30 days. The smolts consumed more of the seaweed-supplemented food relative to the control and there were no mortalities. Compared with the control, the final fish weight, standard length, weight gain and SGR were higher in fish fed diets supplemented with the 3 and 10% seaweed, while growth performance for fish maintained on 6% seaweed remained neutral. Importantly, seaweed supplementation increased protein efficiency ratio (PER) and tended to improve food conversion ratio (FCR). Although the hepatosomatic and visceral indices did not change, whole gut and intestinal weights and lengths were higher in fish maintained on seaweed-supplemented diets suggesting increased retention time and a larger surface area for food digestion and nutrient absorption. Measurement of antioxidant status revealed that seaweed supplementation dose-dependently increased plasma total antioxidant capacity as well as the level of glutathione, and activities of catalase and superoxide dismutase in liver mitochondria. Moreover, seaweed supplementation reduced the effect of acute temperature rise on mitochondrial respiration and proton leak. Overall, these data suggest that AquaArom can be mixed with fish food up to 10% to increase food consumption and enhance growth performance, as well as to improve antioxidant capacity and alleviate adverse effects of stressors such as temperature in fish

Copper metabolism in actively growing rainbow trout (Oncorhynchus mykiss): interactions between dietary and waterborne copper uptake

Juvenile rainbow trout Oncorhynchus mykiss were exposed to diets with low (12.6 nmol g(-1)), normal (50.4 nmol g(-1)) or elevated (4437.5 nmol g(-1)) Cu concentrations in combination with either low (5.8 nmol l(-1)) or normal (48.5 nmol l(-1)) waterborne Cu levels over a 50-day period, during which body mass increased up to fivefold. A nutritional requirement for Cu was demonstrated based on growth response and whole body and tissue Cu status. Simultaneous low Cu levels in both the water and the diet depressed growth by 31 % over 7 weeks. There were reductions in both specific growth rate (SGR, 1.95 versus 2.55 % day(-1)) and food conversion efficiency (FCE, 53-59 % versus 75-80 %) over weeks 0-4, but these effects disappeared in weeks 4-7. Elevated concentrations of dietary Cu did not affect SGR or FCE. Low levels of dietary and waterborne Cu decreased, and high levels of dietary Cu increased, the Cu concentrations in whole body, liver, carcass, gut and gills. Copper levels in the liver strongly reflected the exposure conditions with a corresponding fivefold decrease and a 22-fold increase in Cu concentration. Restricting available Cu caused an exponential decline in whole body Cu concentration from 0.0175 to 0.0069 micromol g(-1) and increased the uptake of waterborne Cu (measured with (64)Cu) by the gills. Conversely, high levels of dietary Cu caused a linear increase in whole body Cu concentration to approximately 0.170 micromol g(-1) and depressed the uptake of waterborne Cu. Waterborne Cu uptake contributed the majority (60 %) of the body's Cu accumulation under Cu-deficient conditions while dietary Cu contributed the majority (99 %) at high dietary levels of Cu. True bioavailability of dietary Cu decreased with increasing levels of dietary Cu concentration, although the absolute amount retained increased. These findings demonstrate an important interaction between dietary and waterborne Cu uptake in fish and provide compelling evidence of a key role for the gill in Cu homeostasis

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.

The thermostability of haemoglobins from the hot-spring fish, Oreochromis alcalicus grahami: comparisons with antarctic and temperate species

1. 1. The thermostability of haemoglobin was measure in three species of fish living at different environmental temperatures (ET). 2. 2. The time (min) for 50% denaturation (T1/2d) of the haemoglobin at 2 mg ml-1 in 50 mM phosphate buffer, pH 7.3 was 46.4±1.7 for Oreochromis alcalicus grahami (ET, 35 to 42°C), 43.1±1.9 for Oreochromis niloticus (ET, 18 to 26°C) and 19.2±0.3 for the Antarctic teleost, Notothenia coriiceps (ET, -1.5 to 1°C) (Mean ±SEM, N=5-7 preparation). In contrast, T1/2d for haemoglobin from birds and mammals is usually in excess of 500 min. 3. 3. These results suggest that the lower thermostability of haemoglobins in fish relative to birds and mammals is not solely a function of differences in body temperature

Effect of TRIS and bicarbonate as buffers on anesthetic efficacy of tricaine methane sulfonate in zebrafish (Danio rerio)

Tricaine methane sulfonate (TMS), often called MS-222, is the most common anesthetic used with fishes. Because it is very acidic (pKa about 3) it must be neutralized especially when used in soft fresh water. Much of the literature on fish anesthetics recommends neutralizing with bicarbonate. However, much of the zebrafish literature uses the protocol in “The Zebrafish Book” that recommends neutralizing with TRIS. Three considerations when comparing these buffers are: first, TRIS has the advantage that the pH tends to remain constant, whereas the pH of solutions containing bicarbonate tends to increase as CO2 diffuses from the water to air; second, the CO2 produced by bicarbonate may have some sedative effects in and of itself; and third, there is some evidence that the efficacy of TMS changes with pH. In the present study, we compared the efficacy of TMS using these two buffers and show that there is no substantial difference in anesthetic properties in zebrafish