Browsing by Author "Bonga, Sjoerd W."
Now showing 1 - 9 of 9
Results Per Page
Sort Options
Item Calcium Homeostasis in Low and High Calcium Water Acclimatized Oreochromis Mossambicus Exposed to Ambient and Dietary Cadmium(2007) Pratap, Harish B.; Bonga, Sjoerd W.The effects of cadmium administered via ambient water (10 µg/l) or food (10 µgCd/fish/day) on plasma calcium, corpuscles of Stannius and bony tissues of Oreochromis mossambicus acclimated to low calcium (0.2 mM) and high calcium (0.8 mM) water were studied for 2, 4, 14 and 35 days. In low calcium water acclimated fish, ambient cadmium induced significant hypocalcemia, while the structure and morphometry of type-1 and type-2 cells of corpuscles of Stannius were not affected on day 2 and 4. Subsequently on day 14 and 35, recovery of plasma calcium to normal levels was observed followed by a decrease in corpuscles of Stannius index (CSI), cell size, volume of granular endoplasmic reticulum (p<0.05) of type-1 cells in both, fish exposed to ambient or dietary cadmium. The type-2 cells were not affected. In high calcium water acclimated fish both, ambient and dietary cadmium caused a significant reduction of plasma calcium levels on day 2 and 4. In these fish, there was a significant transient increase in the size of corpuscles of Stannius on day 4, followed by recovery on day 14 and 35. Ultrastructural observations of corpuscles of Stannius revealed that cadmium did not cause any cellular damage on type-1 and type-2 cells during 35 days exposure. In low or high calcium water acclimatized tilapia exposed to ambient or dietary cadmium had no effect on the calcium and phosphate composition of the scales, operculum and vertebrae. Thus, it is unlikely that recovery of hypocalcemia was due to the dissolution of calcium from bony tissues. This study also revealed that cadmium does not mediate stimulation of the corpuscles of Stannius gland, and that high Ca2+ water had a protective effect against ambient and dietary cadmium.Item Changes in Morphology and Growth of the Mudskipper (Periophthalmus Argentilineatus) Associated with Coastal Pollution(Springer Link, 2006) Kruitwagen, Guus; Pratap, Harish B.; Hecht, Thomas; Bonga, Sjoerd W.In this paper a comparison is made between the growth and morphology of barred mudskippers (Periophthalmus argentilineatus) from six mangrove forests along the coast of Tanzania. The fish populations from unpolluted sites consisted of different size classes, whereas only small sized fish were present in the polluted Mtoni mangroves. Age estimation based on the examination of otoliths revealed that the mudskippers followed similar growth patterns in all sites with limited pollution. However, the age estimates from the polluted Mtoni site revealed an abnormal growth pattern. The occurrence of unilateral anophthalmia in the Mtoni mudskippers suggested that these fish were affected by pollutants during early development. The study showed that the presence of urban and industrial wastes from Dar es Salaam city, as indicated by isotopic enrichment, correlated with abnormal growth and developmental effects in mudskippers. We hypothesize that pollution might also affect fish species that use the mangroves as a temporary habitat.Item Effect of Ambient and Dietary Cadmium on Pavement Cells, Chloride Cells, and Na+/K+-Atpase Activity in the Gills of the Freshwater Teleost Oreochromis Mossambicus at Normal and High Calcium Levels in the Ambient Water(Elsevier, 1993) Pratap, Harish B.; Bonga, Sjoerd W.The effects of cadmium on the gills of the African freshwater cichlid Oreochromis mossambicus in water with normal and relatively high calcium concentrations were studied for periods up to 35 days. The exposure was either through the ambient water or via the diet. Changes in the ultrastructure of the gill epithelium upon exposure to cadmium in the ambient water indicated degeneration of pavement cells and chloride cells, and acceleration in the turnover of the chloride cells. Studies of the Na+/K+-ATPase activity of the gills indicated that a transient increase in the total number of chloride cells was not associated with an increase, but rather a decrease of the total ion-exchange capacity of the chloride cells. Macrophages, lymphocytes, rodlet cells and neutrophilic granulocytes infiltrated the filament epithelium. Recovery of the gills was observed after 35 days. Dietary cadmium caused similar, although delayed, effects. High water calcium concentration reduced the impact of water-borne cadmium, but had no ameliorating effect on dietary cadmium. The data indicate that the disturbance of ion regulation in fish caused by sublethal levels of dietary cadmium is the result of effects of the metals on the gills rather than on the kidney.Item Effect of Waterborne and Dietary Cadmium on Plasma Ions of the Teleost Oreochromis Mossamicus in Relation to Water Calcium Levels(1989) Pratap, Harish B.; Fu, H.; Lock, R. A. C.; Bonga, Sjoerd W.The effects of cadmium administered via ambient water or food on plasma ions of the African freshwater cichlidOreochromis mossambicus were studied for 2, 4, 14, and 35 days, in low calcium (0.2 mM) and high calcium (0.8 mM) water. In low calcium water, an environmentally relevant concentration of 10 g/L water-borne cadmium induced a significant and dramatic hypocalcemia on days 2 and 4. Recovery of plasma calcium was observed on days 14 and 35. Hypermagnesemia was observed on day 2, but normal levels were already found on day 4. In high calcium water adapted fish, the extent of hypocalcemia and hypermagnesemia was less pronounced than in fish from low calcium water. Water-borne cadmium caused no significant changes in plasma phosphate, sodium, potassium, or osmolality. On days 2 and 4, dietary cadmium (averaging 10 g Cd/fish/day) caused hypermagnesemia and hypocalcemia in low calcium wateradapted fish. Recovery was observed on days 4 and 14, respectively. In fish from high calcium water, dietary cadmium caused a significant reduction in plasma calcium on day 4 only; plasma magnesium was unaffected. Hyperphosphatemia was apparent on day 14, irrespective of the water calcium concentration. No changes in plasma sodium, potassium, or osmolality were found.The results show that sublethal concentrations of cadmium, administered via the water as well as via the food, affect calcium and magnesium metabolism in tilapia. High water calcium ameliorates the effects of both water and dietary cadmium on plasma calcium and magnesium levels.Among the various heavy metal pollutants, cadmium is frequently present in natural water bodies as a result of discharges from industrial processes or other anthropogenic contamination. The harmful effects of cadmium on mammals and other terrestrial animals have been widely studied and reviewed (Flicket al. 1971; Vallee and Ulmer 1972; Webb 1979; Korte 1983; Foulkes 1986). Aquatic vertebrates such as fish, live in very intimate contact with the environment through their gills. This makes them very susceptible to aquatic pollutants.Since it is well established that freshwater fish take up most of the ions necessary for homeostasis from the water via the gills (Eddy 1982), cadmiuminduced plasma ionic disturbances are apparently caused by impaired uptake and diffusional losses of ions via these organs (Larssonet al. 1981; Giles 1984). Ionic disturbances have also been reported after exposure of fish to sublethal concentrations of heavy metals. For example, changes in the plasma ionic composition have been observed in fish exposed to copper and zinc (Lewis and Lewis 1971; Spry and Wood 1985), mercury (Locket al. 1981), and chromium (Van der Putteet al. 1983). With respect to cadmium, exposure of rainbow trout to sublethal levels induced hypocalcemia, with reduced plasma sodium, potassium, chloride and increased plasma magnesium (Giles 1984). In European flounder, cadmium-induced hypocalcemia and elevated levels of plasma phosphate, magnesium and potassium were observed (Larssonet al. 1981).In addition to water, food could also be a source of cadmium for fish, since it accumulates in aquatic organisms through trophic transfers (Anonymous 1971; Williams and Giesy 1978; Coombs 1979). Indeed, Bryan (1976) concluded that food as a source of Zn, Mn, Co, and Fe for molluscs, crustaceans and fish was more important than water. From various studies on both water-borne and food-containing metals, reviewed by Dallingeret al. (1987), there is evidence that uptake of heavy metals such as Cd, Cu, Co, Pb, Hg, and Zn from food is also the predominant pathway in freshwater fish. Koyama and Itazawa (1977) reported significant hypocalcemia and elevated plasma phosphate levels in cadmium-fed carps. Similarly, plaice and thornback ray both accumulated more cadmium from food than from seawater (Pentreath 1977). In general, cadmium concentrations in natural waters are extremely low and a more important route of cadmium uptake by fish may be represented via the gut. Experiments with dietary cadmium may therefore yield more representative information for field situations.In this investigation, we have compared the effects of a sublethal concentration of cadmium administered via the water or via the food in the African cichlid fishOreochromis mossambicus (tilapia). Plasma ions and osmolality were determined. Cadmium was administered at sublethal concentrations, in the order of magnitude that may occur in natural waters (10 g Cd/L). In many studies aimed at evaluating the effects of cadmium on fishes, high concentrations (>1 mg Cd/L) of cadmium have been used. Hence severe physiological, behavioral and detrimental effects have been reported. Such high concentrations are rarely found in nature, except in cases of spillage or heavily polluted waters. The Working Group on Cadmium Toxicity (EIFAC 1977) has suggested that chronic exposure to low cadmium concentrations is more relevant to understanding the mechanisms involved in the intoxication process in teleost fish.We further studied the influence of relatively low and high calcium concentration of the water on the toxic effects of cadmium. The effects of water hardness (mainly Ca2+ and Mg2+ ions) on heavy metal toxicity have been demonstrated in various species of teleosts (Prtet al. 1985). Increased toxicity of cadmium to fish in soft water as compared to hard water has been demonstrated in catfish and guppies (Kinkade and Erdman 1975), goldfish (McCartyet al. 1978), striped bass (Palawskiet al. 1985), brook trout (Carrollet al. 1979) and rainbow trout (Calamariet al. 1980; Pascoet al. 1986). Similar observations on teleosts exposed to zinc, copper and lead (Sinleyet al. 1974; Zitko and Carson 1976; Judy and Davies 1979; Laurn and McDonald 1986) indicate a protective role of calcium against the toxic effects of heavy metals. It was also investigated whether the protective effect of the water-calcium concentration is limited to water-borne cadmium only, or also applies to dietary cadm Effect of waterborne and dietary cadmium on plasma ions of the teleost Oreochromis mossamicus in relation to water calcium levels (PDF Download Available).Item Effects of Water-borne Cadmium on Plasma Cortisol and Glucose in the Cichlid Fish Oreochromis Mossambicus(1990) Pratap, Harish B.; Bonga, Sjoerd W.1.1. Freshwater cichlids Oreochromis mossambicus (tilapia) were exposed to 10 μg Cd/l in ambient water for 2,4, 14 and 35 days. Plasma cortisol and glucose levels were determined to evaluate if cadmium induced a typical stress response in these fish.2.2. Exposure to cadmium for 2, 4 and 14 days elicited a significant elevation of plasma cortisol levels.3.3. A significant hyperglycemia occurred on days 2 and 4 in cadmium-exposed fish.4.4. During long-term exposure to cadmium (35 days), the plasma cortisol and glucose levels returned to control values. This recovery after 35 days indicates the ability of tilapia to adapt to low cadmium concentrations in the ambient water.Item Flamingos Mass Mortalities (Harmful Algae 2006)(Elsevier, 2014) Kruitwagen, G.; Hecht, T.; Hecht, Harish B.; Bonga, Sjoerd W.Limnological studies were conducted in three alkaline lakes (Lake Big Momela, Manyara and Embagai) with the aim of investigating the cause of mass mortality of the Lesser Flamingos in Lake Manyara and Lake Big Momela during July–August 2004. High concentrations, up to 150 million filaments per liter of the potentially toxic planktonic cyanobacterium Arthrospira fusiformis were found in surface scum of Lake Big Momela where Lesser Flamingos were dying at a rate of between 15 and 50 individuals per day during the study period. Gut content analyses indicated that A. fusiformis was the main food item in moribund flamingos. Mouse bioassay suggested that the crude microalgal extract dominated by A. fusiformis was toxic with all mice close to death becoming lethargic, with loss of balance, uncoordinated movements, intermittent tremors, dyspnoea with gasping followed by respiratory arrest. This observation gives circumstantial evidence that A. fusiformis at such high concentrations was toxic to the Lesser Flamingo in Lake Big Momela. # 2005 Elsevier B.V. All rights reserved.Item Importance of different carbon sources for macroinvertebrates and fishes of an interlinked mangrove-mudflat ecosystem (Tanzania).(2010) Bonga, Sjoerd W.; Mgaya, Yunus D.; Lugendo, Blandina; Nagelkerken, Ivan; Kruitwagen, G.Mangroves function as important shelter and feeding habitats for marine fauna, but the degree to which mangrove-derived carbon contributes to local food webs has long been debated. In this study, stable isotope analysis was used as a technique to elucidate the role of mangrove carbon in the diets of the macroinvertebrate and fish fauna of an intertidal fringing mangrove forest and adjacent intertidal/subtidal mudflats in a macrotidal Tanzanian estuary. The expectation was that sessile species and those with low motility depend to a larger extent on local carbon sources than highly motile species. A clear distinction in δ13C was present between primary producers from mangrove and mudflat habitats. Macroinvertebrates revealed a gradient in their δ13C where Sesarma crabs were the only species that directly utilised mangrove carbon by feeding on mangrove leaves/detritus. Uca crabs and the gastropod Littoraria scabra showed a higher dependence on microphytobenthos from the mangrove substratum. Among the fish fauna, the amphibious mudskipper was the only species to which the mangroves were accessible during low tide. Consequently this was the only fish species for which it was clear that it fed in the mangrove habitat, most commonly on mangrove-associated Uca crabs. All other species of sessile as well as motile macroinvertebrates and fish from the mangrove and mudflat habitat showed a high degree of utilisation of mudflat carbon. Overall, mangrove carbon thus contributed little to the mangrove and mudflat food webs, despite the high tidal amplitude and the resulting potential for exchange of carbon and fauna in the estuary studied here. Utilisation of mangrove carbon appears to depend more on the ecology of the species in consideration (e.g., species-specific use of zones within the mangrove habitat) than on their potential motility or tolerance to exposure during low tide.Item Mineral Composition and Cadmium Accumulation in Oreochromis mossambicus Exposed to Waterborne Cadmium(2004) Pratap, Harish B.; Bonga, Sjoerd W.Item Status of Pollution in Mangrove Ecosystems along the Coast of Tanzania(2008) Kruitwagen, Guus; Pratap, Harish B.; Covaci, Adrian; Bonga, Sjoerd W.Worldwide, mangrove forests are under threat of the accumulation of pollutants, which may be imported into mangrove ecosystems through the waters from rivers and streams. The distribution, behaviour, and accumulation of these imported chemicals in the ecosystem are largely defined by the hydrology of the mangroves, the geochemical properties of sediments, and the class of pollutants (e.g. heavy metals, organotins, organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs)). The properties of the mangrove sediments provide good binding opportunities for a number of these pollutants: hydrophobic organic pollutants adsorb to the extensive surfaces that are provided by the fine particulate sediments of estuaries and mangroves. Metals are trapped in mangrove sediments through the formation of complexes with sulphides (Lacerda et al., 1991), particulate organic carbon, or iron oxyhydroxides (Chapman et al., 1998). As a consequence, anthropogenic pollutants are filtered from the water layer and accumulate in the sediments of estuaries and mangroves (Bayen et al., 2005; Bhattacharya et al., 2003; Tam and Wong, 1995; Tam and Yao, 2002). Depending on the speciation of chemicals, the pollutants can accumulate in the tissues of biota