Local Fish Species Research Articles

The larva ofTetracanthagyna plagiata, with notes on its biology and comparisons with congeneric species (Odonata: Aeshnidae)

The F stadium larva of both sexes of Tetracanthagyna plagiata is described and figured based on exuviae from which confirmed adult specimens had been reared. Larvae were originally collected in small, slow forest streams in Singapore, and in captivity were fed on local shrimp and small fish species. The known larvae of Tetracanthagyna species, T. degorsi, T. plagiata and T. waterhousei are compared and characters for separating the three species are tabled and figured. T. plagiata larvae reared in captivity exhibited obligate ambush predation and ballistic defaecation.

Dual influences of ecosystem size and disturbance on food chain length in streams

The number of trophic transfers occurring between basal resources and top predators, food chain length (FCL), varies widely in the world's ecosystems for reasons that are poorly understood, particularly for stream ecosystems. Available evidence indicates that FCL is set by energetic constraints, environmental stochasticity, or ecosystem size effects, although no single explanation has yet accounted for FCL patterns in a broad sense. Further, whether environmental disturbance can influence FCL has been debated on both theoretical and empirical grounds for quite some time. Using data from sixteen South Island, New Zealand streams, we determined whether the so-called ecosystem size, disturbance, or resource availability hypotheses could account for FCL variation in high country fluvial environments. Stable isotope-based estimates of maximum trophic position ranged from 2.6 to 4.2 and averaged 3.5, a value on par with the global FCL average for streams. Model-selection results indicated that stream size and disturbance regime best explained across-site patterns in FCL, although resource availability was negatively correlated with our measure of disturbance; FCL approached its maximum in large, stable springs and was <3.5 trophic levels in small, fishless and/or disturbed streams. Community data indicate that size influenced FCL, primarily through its influence on local fish species richness (i.e., via trophic level additions and/or insertions), whereas disturbance did so via an effect on the relative availability of intermediate predators (i.e., predatory invertebrates) as prey for fishes. Overall, our results demonstrate that disturbance can have an important food web-structuring role in stream ecosystems, and further imply that pluralistic explanations are needed to fully understand the range of structural variation observed for real food webs.

Diet composition and feeding of European anchovy Engraulis encrasicolus in Kiel Bight, western Baltic Sea

Diet composition of the expanding southern species European anchovy Engraulis encrasicolus in the western Baltic Sea was investigated. Results revealed an interesting case of bentho-pelagic coupling with potential implications for local fish species through competition for food resources.

Use of Habitats as Surrogates of Biodiversity for Efficient Coral Reef Conservation Planning in Pacific Ocean Islands

Marine protected areas (MPAs) have been highlighted as a means toward effective conservation of coral reefs. New strategies are required to more effectively select MPA locations and increase the pace of their implementation. Many criteria exist to design MPA networks, but generally, it is recommended that networks conserve a diversity of species selected for, among other attributes, their representativeness, rarity, or endemicity. Because knowledge of species' spatial distribution remains scarce, efficient surrogates are urgently needed. We used five different levels of habitat maps and six spatial scales of analysis to identify under which circumstances habitat data used to design MPA networks for Wallis Island provided better representation of species than random choice alone. Protected-area site selections were derived from a rarity-complementarity algorithm. Habitat surrogacy was tested for commercial fish species, all fish species, commercially harvested invertebrates, corals, and algae species. Efficiency of habitat surrogacy varied by species group, type of habitat map, and spatial scale of analysis. Maps with the highest habitat thematic complexity provided better surrogates than simpler maps and were more robust to changes in spatial scales. Surrogates were most efficient for commercial fishes, corals, and algae but not for commercial invertebrates. Conversely, other measurements of species-habitat associations, such as richness congruence and composition similarities provided weak results. We provide, in part, a habitat-mapping methodology for designation of MPAs for Pacific Ocean islands that are characterized by habitat zonations similar to Wallis. Given the increasing availability and affordability of space-borne imagery to map habitats, our approach could appreciably facilitate and improve current approaches to coral reef conservation and enhance MPA implementation.

Fish dispersal in a seasonal wetland: influence of anthropogenic structures

Knowledge of fish dispersal routes when exploiting temporary habitat is important for understanding the ecology of species and for designing and conducting conservation and land-management activities. We evaluated fish dispersal in a network of seasonal habitats and a permanent fish source (a lake) in a subtropical wetland, in Florida, sampled biweekly from May 2002 to May 2003. Fish dispersal routes were influenced by (1) local physical conditions, (2) anthropogenic alterations and (3) fish species and size. Fish from the source dispersed into 9 of the 25 seasonal sites evaluated, via temporarily formed dispersal corridors between the source and the sites. Low connection depths along the corridors were a key factor, allowing small-bodied species (e.g. Gambusia holbrooki, Elassoma evergladei) to travel farther than large-bodied fish (e.g. Erimyzon sucetta, Lepomis macrochirus). Fish travelled distances of 0.7–4 km. Anthropogenic structures both enhanced (ditches, sand roads) and blocked (a railroad, soil dumps) fish dispersal routes. We demonstrated extensive opportunistic use by fish of seasonal wetlands. Our results indicated that anthropogenic alterations to the landscape can provide habitat for native fish and also allow dispersal of non-native fish and thus should be implemented with care.

Impact of shark-feeding tourism on surrounding fish populations off Moorea Island (French Polynesia)

Shark feeding is widespread throughout tropical, subtropical and temperate marine ecosystems and gives rise to controversy because there is little consensus regarding its management. There are few comprehensive reports that consider how shark feeding with bait might impact local fishes, despite the development of this practice during the last few decades. Although shark feeding might theoretically have parasitological effects on local non-target fish species in the vicinity of feeding areas, this aspect has never been investigated. During an extensive parasitological survey conducted between 2005 and 2007, a total of 1117 fish belonging to six common grouper and snapper species were sampled throughout the entire north coast of Moorea Island (French Polynesia), encompassing three localities where feeding has occurred frequently since the 1990s. Parasites exhibited no spatial patterns except for the infections on the blacktip grouper (Epinephelus fasciatus). On this species, the prevalence of larval cestodes that parasitise sharks as adults and the intensity of their infestation were significantly higher around shark-feeding localities compared with non-shark-feeding localities. Our results suggest for the first time that although long-term shark feeding has parasitological implications, the impacts appear limited, only involve cestode larvae from one host species and do not seem to affect the health of the fish we studied.

Persistent organochlorine pollutants and toxaphene congener profiles in bottlenose dolphins (Tursiops truncatus) frequenting the Turtle/Brunswick River Estuary, Georgia, USA

Although the Turtle/Brunswick River Estuary (TBRE) in coastal Georgia (USA) is severely contaminated by persistent organochlorine pollutants (POPs), little information regarding POPs in higher-trophic-level biota in this system is available. In the present study, polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs; including DDTs, chlordanes, and mirex), and chlorinated monoterpenes (toxaphene) were measured using gas chromatography with electron-capture detection and gas chromatography with electron-capture negative ion mass spectrometry (GC-ECNI-MS) in blubber of free-ranging and stranded bottlenose dolphins (Tursiops truncatus). Mean total PCBs (78.6 +/- 32.4 microg/g lipid) and toxaphene (11.7 +/- 9.3 microg/g lipid) were significantly higher in dolphins sampled in the TBRE than in dolphins stranded near Savannah (GA, USA) 80 to 100 km to the north. Levels of OCPs were several-fold lower than levels of PCBs; moreover, PCBs comprised 81 and 67% of the total POP burden in TBRE and non-TBRE dolphins, respectively. Analyses with GC-ECNI-MS revealed that 2,2,5-endo,6-exo,8,8,9,10-octachlorobornane (P-42a), a major component in technical toxaphene and a major residue congener in local estuarine fish species, was the most abundant chlorobornane in both sets of blubber samples. Mean total POP concentrations (sum of PCBs, OCPs, and toxaphene) approached 100 microg/g lipid for the TBRE animals, well above published total PCB thresholds at which immunosuppresion and/or reproductive anomalies are thought to occur. These results indicate extended utilization of the highly contaminated TBRE as habitat for a group of coastal estuarine dolphins, and they further suggest that these animals may be at risk because of elevated POP concentrations.

A Marquesan coral reef (French Polynesia) in historical context: an integrated socio‐ecological approach

Abstract Marine biologists are increasingly aware of the impact that even small human populations can have on coral reefs around the world, while conservationists and fisheries managers have a growing appreciation of the importance of culturally informed management strategies in coral reef conservation efforts. Despite these recognitions, however, examples of integrated field studies are limited. In this paper evidence from various disciplines is used to study the interaction between humans and one of the largest reefs in the Marquesas Islands, at Anaho Bay, Nuku Hiva Island, with the aim of assessing possible anthropogenic impacts over time. First, it reports on a marine biological survey of the benthic substrates of the bay and the taxonomic composition and spatial distributions of the local fish species. Second, it draws on results from an ongoing archaeological study and integrates these with interviews of village elders to gain a historical perspective on the reef and potential human impacts. The biological results indicated that the reef is in a state of decline, although fish densities are moderately high. The archaeological evidence, in turn, demonstrates that human populations have occupied this valley for at least the last 700 years. Throughout this period marine resources have been an important source of both food and raw materials for tools. The archaeological study also highlights aspects of landscape change, both natural and human‐induced, that probably have been detrimental to reef health. Using the combined biological and anthropological data, this paper considers the nexus of factors that have led to the current reef conditions and considers management issues for the future. Key in this regard are processes that have initiated erosion and soil run‐off, and fluctuations in the local human populations. Copyright © 2008 John Wiley &amp; Sons, Ltd.

High fish consumption in French Polynesia and prenatal exposure to metals and nutrients.

French Polynesians consume high quantities of fish and are therefore exposed to seafood-related contaminants such as mercury (Hg) or lead (Pb) and nutrients such as iodine, selenium and long chain polyunsaturated fatty acids (LC-PUFAs). As the developing foetus is sensitive to contaminants and nutrients, a cross-sectional study was conducted in French Polynesia in 2005-2006 to assess prenatal exposure to contaminants and nutrients through fish consumption. Two hundred and forty one (241) delivering women originating from all islands of French Polynesia were recruited and agreed to answer questions on fish consumption and gave permission to collect umbilical cord blood for metals and nutrients analyses. All parameters were found in high concentrations in cord blood samples except for lead. Mercury concentrations averaged 64.6 nmol/L (or 13 microg/L) with values ranging from 0.25 to 240 nmol/L. Of the sample, 82.5% had Hg concentrations above the US-EPA blood guide-line of 5.8 microg/L. Tuna was the fish species which contributed the most to Hg exposure. High selenium and LC-PUFAs may counterbalance the potential risk of prenatal exposure to Hg in French Polynesia. Due to the high fish consumption of mothers, Polynesian newborns are prenatally exposed to high doses of mercury. Although selenium and omega-3 fatty acids may counteract mercury toxicity, informing pregnant women on both the mercury and nutrient content of local fish species is important.

Geographic specificity of Aroclor 1268 in bottlenose dolphins (Tursiops truncatus) frequenting the Turtle/Brunswick River Estuary, Georgia (USA)

Coastal marine resources are at risk from anthropogenic contaminants, including legacy persistent organic pollutants (POPs) with half-lives of decades or more. To determine if polychlorinated biphenyl (PCB) signatures can be used to distinguish among local populations of inshore bottlenose dolphins ( Tursiops truncatus) along the southeastern U.S. coast, blubber from free-ranging and stranded animals were collected along the Georgia coast in 2004 and analyzed for PCB congeners using gas chromatography with electron capture and negative chemical ionization mass spectrometric detection (GC-ECD and GC-NCI-MS). Mean total PCB concentrations (77 ± 34 μg/g lipid) were more than 10 fold higher and congener distributions were highly enriched in Cl 7–Cl 10 homologs in free-ranging animals from the Turtle/Brunswick River estuary (TBRE) compared with strandings samples from Savannah area estuaries 90 km to the north. Using principal components analysis (PCA), the Aroclor 1268 signature associated with TBRE animals was distinct from that observed in Savannah area animals, and also from those in animals biopsied in other southeastern U.S estuaries. Moreover, PCB signatures in dolphin blubber closely resembled those in local preferred prey fish species, strengthening the hypothesis that inshore T. truncatus populations exhibit long-term fidelity to specific estuaries and making them excellent sentinels for assessing the impact of stressors on coastal ecosystem health.

Environmental fate and non-target impact of glyphosate-based herbicide (Roundup ®) in a subtropical wetland

Mai Po Nature Reserve (Hong Kong) is an internationally important wetland for waterbirds. Roundup ®, a formulation based on glyphosate, has been used to control the widespread weeds within the reserve for many years but the fate and non-target impact of the herbicide is unknown. To fill this knowledge gap, we applied Roundup ® by hand-held sprayer to an estuarine and a freshwater pond in the dry season of year 2002. The surface water and sediment were sampled routinely for glyphosate concentrations following one month of application. In situ bioassays using local edible fish species were performed along with the herbicide application. Up to 52% of glyphosate in the surface water was transported to the unapplied regions by wind-driven current in the estuarine pond at 1 DPT (day post treatment). For both ponds, glyphosate concentrations in the water decreased rapidly after 1–3 DPT, but then decreased gradually over time. Both physical adsorption to the bottom sediments and microbial degradation are thought to contribute to these decreases. Interestingly, the persistence of glyphosate in the freshwater pond was longer than in the estuarine system, which is likely due to the considerably higher concentrations of chelating metals (i.e. Cu and Fe) present in the sediment (4.5 and 11-fold higher, respectively) which potentially reduced the bioavailability of glyphosate to the microbial decomposers. Lastly, fishes used in the in situ bioassays (both in applied and unapplied areas) showed similar survival rates, indicating that the use of Roundup ® at the provided application rate posed no serious hazard.

Evaluation of Alachlor Herbicide Impacts on Nile Tilapia (Oreochromis niloticus) using Biochemical Biomarkers

Herbicide application as a part of agricultural processes may have impacts on nontarget organisms, especially aquatic lives and their environment. Often as a component of sustainable agriculture in tropical countries, fish farming is practiced on farmlands. Thus, to supplement risk assessment studies, it is important to obtain information on the effects these xenobiotics have on local species. Alachlor (2-chloro-N-[2,6-diethyphenyl]-N-[methoxymethyl)acetamide]) is one of the most widely used chloroacetanilide herbicides for the control of annual grasses and many broadleaf weeds. Its extensive use and its persistence in ground and surface water have posed potential risks for human exposure, not only to professional applicators and farmers, but also to general populations. There have been numerous studies on alachlor, but much less investigation of its effects on fish and aquatic species. Alachlor has been listed as carcinogenic and highly toxic to humans despite slight acute toxicity (Orme and Kegley, 2005). Thus, many countries have banned alachlor from their markets. The main objective of this study was to evaluate the effects of alachlor herbicides on relative activities of acetylcholinesterase (AChE) and glutathione-S-transferase (GST) in various tissues of Nile tilapia (Oreochromis niloticus). Nile tilapia, a local fish species of high economic importance, is a benthic omnivorous cichlid commonly found in fish ponds and streams of tropical countries, including Thailand. The effects of short-term contaminant exposure, measured as the biochemical and physiologic responses in Nile tilapia, may be used to assess and monitor alachlor contamination in agricultural settings.

Direct evaluation of macroalgal removal by herbivorous coral reef fishes

Few studies have examined the relative functional impacts of individual herbivorous fish species on coral reef ecosystem processes in the Indo-Pacific. This study assessed the potential grazing impact of individual species within an inshore herbivorous reef fish assemblage on the central Great Barrier Reef (GBR), by determining which fish species were able to remove particular macroalgal species. Transplanted multiple-choice algal assays and remote stationary underwater digital video cameras were used to quantify the impact of local herbivorous reef fish species on 12 species of macroalgae. Macroalgal removal by the fishes was rapid. Within 3 h of exposure to herbivorous reef fishes there was significant evidence of intense grazing. After 12 h of exposure, 10 of the 12 macroalgal species had decreased to less than 15% of their original mass. Chlorodesmis fastigiata (Chlorophyta) and Galaxaura sp. (Rhodophyta) showed significantly less susceptibility to herbivorous reef fish grazing than all other macroalgae, even after 24 h exposure. Six herbivorous and/or nominally herbivorous reef fish species were identified as the dominant grazers of macroalgae: Siganus doliatus, Siganus canaliculatus, Chlorurus microrhinos, Hipposcarus longiceps, Scarus rivulatus and Pomacanthus sexstriatus. The siganid S. doliatus fed heavily on Hypnea sp., while S. canaliculatus fed intensively on Sargassum sp. Variation in macroalgal susceptibility was not clearly correlated with morphological and/or chemical defenses that have been previously suggested as deterrents against herbivory. Nevertheless, the results stress the potential importance of individual herbivorous reef fish species in removing macroalgae from coral reefs.

Sampling effort and fish species richness in small terra firme forest streams of central Amazonia, Brazil

Small streams are important components of the landscape in terra firme forests in central Amazonia and harbor a large number of fish species. Nevertheless, the lack of a common sampling protocol in studies of this ichthyofauna hinders comparisons among available results. This study evaluates how the length of stream reach sampled affects estimates of local fish species density in 1st, 2nd, and 3rd order streams, and proposes a mean minimum sampling length that best approximates the absolute number of species in a given stream segment. We sampled three streams in the Biological Dynamics of Forest Fragments Project's study sites, between May and August 2004. At each stream, one 1st order, one 2nd order, and one 3rd order segment was sampled. We sampled five 20-m reaches in each stream segment. Three to four people collected along each reach for 45 to 60 minutes. We used Jaccard's coefficient to estimate the similarity of species composition among stream reaches and segments. Estimates of species richness were obtained with Jackknife 1 and Bootstrap algorithms and species accumulation curves. We used simple linear regressions to look for relationships between species density and fish abundance and between species density and the volume of 100-m stream segments. Species density in 1st order stream reaches was slightly higher than in 2nd and 3rd order stream reaches, whereas fish abundance was apparently higher in 3rd order reaches. Similarity in fish species composition between 20-m reaches was low for all studied streams. Species density values in pooled 100-m stream segments represented 71.4% to 94.1% of the estimated values for these streams. Species density showed a direct relationship both with volume of the sampled stream segment and fish abundance. It seems plausible that larger streams contain a higher number of microhabitat types, which allow for the presence of more fish species per stream length. Based on the values of asymptotes and equations for species accumulation curves, the mean minimum sampling length that best estimates the absolute number of species in a stream segment is 180 m ± 20 sd for 1st order segments; 213 m ± 23 sd for 2nd order segments, and 253 m ± 30 sd for 3rd order stream segments.

Effects of habitat complexity on Caribbean marine fish assemblages

Sets of artificial reefs were replicated in 5 bays off Tortola in the British Virgin Islands to investigate the effects of habitat complexity on fish assemblages. Increasing percentage hard sub- strate and the number of small reef holes increased fish abundance on reefs. The observed number of species (Sobs) occurring on each reef increased with increasing rugosity, variety of growth forms, percentage hard substrate, and variety of refuge hole sizes. A rarefied or abundance-corrected spe- cies richness measure (Srare) was calculated to take the varying fish abundances into account. After this correction, rugosity was the only variable that significantly increased fish species-richness. Experimental reefs of different height (20 and 60 cm) did not have significantly different fish abun- dance or species richness. The presence of long-spined sea urchins Diadema antillarum increased Sobs and total fish abundance on artificial rock-reefs and in seagrass beds, but the effect was most pronounced in seagrass beds where shelter was a strongly limiting factor. These results indicate that complex habitats or animals such as D. antillarum that provide shelter to fish are essential for main- taining fish biodiversity at local scales. The most important aspects of complexity are rugosity, hard substrate and small refuge holes. Artificial reefs may be used to mitigate habitat damage in impacted areas, and if management objectives are to increase local fish abundance and species richness, the reefs should provide a stable substrate where this is unavailable, have a rugose surface with many small refuge holes, and have a variety of growth forms.

Trials of rabbitfish Siganus rivulatus production in floating cages in the Red Sea

Three trials were conducted on an important local fish species the Rabbitfish Siganus rivulatus in the Red Sea at the Fish Farming Center, Jeddah, Saudi Arabia. The first trial was to investigate the production of this species in three densities (80, 100 and 120/ m³). In the second trial S. rivulatus was reared in two different sets of floating cage sizes (small of 10m³ and large of 60m³). The last trial was carried out to determine the suitable feeding rate (7.5% and 15% of body weight) of a locally formulated feed. Results of the first trial showed no significant difference in the final weight and survival rates at the three stocking rates of S. rivulatus. Correlation analysis showed a negative influence of increasing stocking density on growth and survival. However, for the second and the third trials; a highly significant difference (P<0.05) was observed between feeding rates and cage sizes favoring the lower feeding rate of 7.5% and the smaller cages of (10m³) respectively.

Environmental Factors Influencing Local Fish Species Richness and Differences between Hydroregions in South‐Western France

AbstractThe aim of this study was to investigate the influence of 5 typological variables on the spatial distribution patterns of fish species richness in south‐western France, and, subsequently, to analyse differences in the number of species occurring in 6 major hydroregions located within the overall study area. The data were collected at 329 sampling sites. General Linear Modelling was used to assess the influence of each typological variable on local fish species richness, and to determine the differences in local fish species richness between the 6 hydroregions. Local species richness was significantly influenced by altitude, slope and catchment area, whereas distance from the source and stream width showed no significant relations with local richness. The Côteaux de Gascogne hydroregion had a significantly lower species richness, whereas no significant differences occurred among other neighbouring hydroregions. These results were congruent with the spatial distribution patterns of freshwater invertebrate species richness in the area, which were analysed in previous studies. At such a regional scale, we suggest that congruent patterns between fish and invertebrate species richness are almost certainly a result of similar responses by different taxa to environmental conditions, rather than to biotic interactions. (© 2004 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Technical and economical evaluation of periphyton-based cage culture of tilapia ( Oreochromis niloticus) in tropical freshwater cages

A 3-month study (March–June) was carried out in the Meghna–Gumti River (Bangladesh) to assess the potential for periphyton-based cage aquaculture. The growth of genetically improved farmed tilapia (GIFT) strain ( Oreochromis niloticus) was monitored during a trial conducted in nine 2.5-m 3 floating cages. The importance of periphyton in tilapia diets was assessed using three treatments. In the first treatment, the periphyton biomass was increased using additional substrates placed in the cage. In the second treatment, additional substrates were used and the diet was supplemented with a locally available compound feed. The third treatment had no additional substrate but received some supplementary feed. The effect of grazing on periphyton biomass was also assessed in a parallel experiment. Biomass was assessed by measuring ash, ash-free dry weight (AFDW), chlorophyll a, phaeopigments and respiration. Net production of fish ranged from 0.12 to 0.19 kg m −3 month −1 and specific growth rate (SGR) from 0.7% to 0.95% body weight day −1. Jaw abnormalities affected 33% of fish and reproduction was observed in fish as small as 35 g. Productivity of a 1 m 2 of net located in the uppermost 50 cm of the water column, however, was estimated at 0.94 g fish day −1. The periphyton biomass dropped in just 2 days from 1.12 to 0.34 mg/cm 2 after the introduction of the fish in the cage. The fish fed on plankton, artificial supplementary feed and periphyton growing on substrate in the cage. Filter feeding and grazing on the cage net appeared to be the most important source of energy. The effect of the additional substrates placed in the cages was marginal. The periphyton-based cage aquaculture described here was not economically viable and the main economic constraints were the costs of cage material (net and bamboo poles) and fry. Periphyton-based cage culture could be made more profitable by using local fish species, less expensive cage design, better substrate and by using adapted management techniques to improve periphyton productivity.

Presence of Planktothrix sp. and cyanobacterial toxins in Lake Ammersee, Germany and their impact on whitefish (Coregonus lavaretus L.).

Due to the increasing oligotrophy of Lake Ammersee, southern Germany, metalimnic Planktothrix have become one of the dominant planktonic species causing regular blooms. Whitefish (Coregonus lavaretus) is the dominant local fish species with great importance for the fishing industry. Recently, whole age groups of this fish species have disappeared and since 1991, average body-weight has decreased. The causes for this remain unclear. Planktothrix species produce the cyclic peptide toxin desmethyl microcystin-RR, which inhibits glycogen metabolism and has detrimental effects on the development of aquatic organisms. During blooms, gut contents of whitefish displayed a blue discoloration, possibly representing phycobiliproteins typical for cyanobacteria. This study aimed to elucidate the impact of Planktothrix blooms on fish population dynamics. Planktothrix cell counts, performed by epifluorescence microscopy, showed blooms to contain up to 80,000 cells/ml. Microcystin levels of 1-5 micrograms/mg dry weight in Planktothrix extracts and 0.08 microgram/l in water samples, were determined via HPLC and protein-phosphatase inhibition assay. Planktothrix filaments were detected in gut contents of whitefish. In addition, microcystins could be detected in gut contents via ELISA. Similarly, immunoprobing with microcystin-antibodies demonstrated microcystin-protein adducts in liver homogenates of whitefish caught during Planktothrix blooms. Furthermore, Planktothrix extracts proved cytotoxic to trout hepatocytes as determined by MTT reduction. Whitefish eggs and larvae, obtained during blooms in winter 1998 and 2000 in a Lake Ammersee hatchery, were studied for developmental progress. Malformations typical for cyanobacterial toxin exposure were observed.

Methodology for Predicting Cooling Water Effects on Fish

The mathematical model presented here predicts the long-term effects of once-through cooling water systems on local fish populations. The fish life cycle model simulates different life stages of fish by using appropriate expressions representing growth and mortality rates. The heart of the developed modeling approach is the prediction of plant-caused reduction in total fish population by estimating recruitment to adult population with and without entrainment of ichthyoplankton and impingement of small fish. The model was applied to a local fish species, gilthead (Sparus aurata), for the case of a proposed power plant in the Aegean region of Turkey. The simulations indicate that entrainment and impingement may lead to a population reduction of about 2% to 8% in the long run. In many cases, an impact of this size can be considered rather unimportant. In the case of sensitive and ecologically valued species facing extinction, however, necessary precautions should be taken to minimize or totally avoid such an impact.