Patrick Kestemont

Effects of microcystins on fish

Microcystins (MCs) are hepatotoxic heptapeptides released into water during or on senescence of cyanobacterial blooms. This review details the different effects of the MCs on fish and discusses their potential consequences in aquatic food webs. In early life stages, exposure to MCs causes, in a dose-dependent manner, perturbations to embryonic hatching, decrease in survival and growth rate, as well as histopathological effects (enlarged and opaque yolk sac, small head, curved body and tail, hepatobiliary abnormalities, ultrastructural alterations in hepatocytes, heart rate perturbations). In adults and juveniles, field and experimental studies demonstrated that after ingestion MCs accumulate mainly in liver but can also be found in muscle and viscera. Microcystin exposure has been shown to affect growth rate and osmoregulation, increase liver enzyme activities in the serum and heart rate, modify behavior, and exert histopathological effects in the liver, intestine, kidneys, heart, spleen, or gills, but the degree to which these effects were seen depends on the exposure route. The detoxication pathway of MCs in fish begins with a conjugation reaction to glutathione catalyzed by glutathione S-transferases, and this is comparable to the reaction demonstrated in other organisms, from plants to mammals. It appears that MC concentrations found in nature can potently affect several trophic levels in the aquatic ecosystems, in particular by inducing failure of sensitive stages (e.g., fish fry) to develop and accumulating in the food chains. The need of further quantitative studies on the sublethal effects, accumulation, and fate of MCs in aquatic food chains still remains.

Size heterogeneity, cannibalism and competition in cultured predatory fish larvae: biotic and abiotic influences

Growth heterogeneity is a central problem in larviculture and especially in predatory species. It can be influenced by a wide range of intrinsic and environmental factors, of which the respective influences are largely unknown. The role of non-interactive (temperature, day length, light intensity, food availability and composition) and interactive factors (stocking density, initial size heterogeneity, hatching time) on growth, survival and size heterogeneity was measured in larvae and post-larvae of the European seabass Dicentrarchus labrax and Eurasian perch Perca fluviatilis. Embryos hatching later than others were found less competitive than those hatching earlier in both species, but to a greater extent in perch. By contrast, the final size heterogeneity in both species was independent from the initial size heterogeneity or recurrent size sorting. High stocking density had a positive effect on perch larvae, no effect on seabass larvae and a negative impact on the post-larvae of both species, owing principally to density-dependent access to food. Day length and light intensity produced contrasting results in larvae and post-larvae. Larvae of both species performed better under bright light and continuous day length. Post-larvae of seabass performed equally well at different light levels but did better under short day lengths, whereas post-larvae of perch were unaffected by day length but performed better under reduced light levels. Increasing food availability resulted in increasing performance of perch larvae, although cannibalism was higher for submaximal than for maintenance rations. The similarity between the two species at the larval stage, and differences at the post-larval stage can be accounted for by the increasing specialisation towards specific environments and niches. Regarding the impact of rearing factors on growth, survival and size heterogeneity, interactive variables impacted essentially on growth and survival, whereas size heterogeneity was chiefly influenced by non-interactive variables, either directly or indirectly via interactive mechanisms such as cannibalism and size-dependent mortality.

Hepatic accumulation and effects of microcystin-LR on juvenile goldfish Carassius auratus L.

After intraperitoneal injection of microcystin-LR (MC-LR) (125 microg kg(-1) body wt.), the concentration of MC-LR in the liver of juvenile goldfish Carassius auratus (30 g body wt.) was assayed by a modified protein phosphatase inhibition method. A temporary accumulation occurred from 3 to 48 h post-injection, followed by a significant decrease between 48 and 96 h. Under our experimental conditions, contamination by MC-LR did not change ionic homeostasis, as attested by blood osmolality values and gill Na(+)/K(+) ATPase activity. Light microscopy observations revealed lesions and cellular necrosis progression, which was concomitant with an increase in enzyme activity of plasma aspartate aminotransferase (AspAT), alanine aminotransferase (AlaAT) and L-lactate dehydrogenase (LDH) and with a decrease of hepatic glutathione-S-transferase (GST) activity. Structural alterations and enzymatic activity modifications became significant within 24 h post-injection. Recovery of hepatocytes on day 21 after MC-LR injection was evident, together with a decrease in the MC-LR equivalent content of the liver.

The effects of estrogenic and androgenic endocrine disruptors on the immune system of fish: a review

During the last decade, a number of studies have shown that, in addition to their classically described reproductive function, estrogens and androgens also regulate the immune system in teleosts. Today, several molecules are known to interfere with the sex-steroid signaling. These chemicals are often referred to as endocrine disrupting contaminants (EDCs). We review the growing evidence that these compounds interfere with the fish immune system. These studies encompass a broad range of approaches from field studies to those at the molecular level. This integrative overview improves our understanding of the various endocrine-disrupting processes triggered by these chemicals. Furthermore, the research also explains why fish that have been exposed to EDCs are more sensitive to pathogens during gametogenesis. In this review, we first discuss the primary actions of sex-steroid-like endocrine disruptors in fish and the specificity of the fish immune system in comparison to mammals. Then, we review the known interactions between the immune system and EDCs and interpret the primary effects of sex steroids (estrogens and androgens) and their related endocrine disruptors on immune modulation. The recent literature suggests that immune parameters may be used as biomarkers of contamination by EDCs. However, caution should be used in the assessment of such immunotoxicity. In particular, more attention should be paid to the specificity of these biomarkers, the external/internal factors influencing the response, and the transduction pathways induced by these molecules in fish. The use of the well-known mammalian models provides a useful guide for future research in fish.

The effect of PIT tags on growth and physiology of age-0 cultured Eurasian perch Perca fluviatilis of variable size.

Abstract For many biological reasons, it is often necessary to tag and monitor fish from a very early age. However, tagging can adversely affect fish, especially for high tag to body weight ratios. To determine the minimum size for passive integrated transponders (PIT) tagging in juvenile perch Perca fluviatilis , surgical implantation was evaluated in fish ranging from 1.67 to 10.62 g (55–96 mm FL). The survival, gonadal development, and capacity of tagged perch to store abdominal fat was affected neither by the tagging procedure, tag presence, nor tag to body weight ratio. Four months after tagging, no tag had caused internal damage or had been expelled, despite about 95% of them becoming encapsulated by host tissues. Negative effects from tagging were restricted to slower healing rates, and depressed growth of fish with high tag to body weight ratios during the first post-tagging days, which was compensated for by catch-up growth within less than 2 weeks. Surgical PIT tagging can be confidently applied to perch weighing less than 2 g, but the collection of biological data should be delayed by about 2 weeks after tagging. X-ray photographs revealed variable orientations of tags (95% CI: 26°) and slight (ca. 4°) changes of orientation over time. These discrepancies may affect the probability that the tag is detected by automatic data entry stations, and should be compensated for by using smaller antennas (≤87% of maximal antenna size).

Corticosteroids: Friends or foes of teleost fish reproduction?

Reproduction in vertebrates is controlled by the Hypothalamus-Pituitary-Gonad axis and the main hormone actions have been extensively described. Still, despite the scattered information in fish, accumulating evidence strongly indicates that corticosteroids play essential roles in reproductive mechanisms. An integrative approach is important for understanding these implications. Animal husbandry and physiological studies at molecular to organismal levels have revealed that these corticosteroids are regulators of fish reproductive processes. But their involvements appear strongly contrasted. Indeed, for both sexes, corticosteroids present either deleterious or positive effects on fish reproduction. In this review, the authors will attempt to gather and clarify the available information about these physiological involvements. The authors will also suggest future ways to prospect corticosteroid roles in fish reproduction.

Comparison of the nutritional status of goldfish (Carassius auratus) larvae fed with live, mixed or dry diet

Abstract The aim of this work was to study the influence of three diets on the nutritional status of goldfish larvae. The evaluation criteria for food quality were: growth and survival of the larvae, proteolytic activity of a trypsin-like enzyme as well as the structure and ultrastructure of the hepatopancreas. Immediately after the resorption of the yolk sac, the goldfish larvae were distributed into 9 rearing tanks (700 larvae each) under constant photoperiod (L:D 16:8) and temperature (24°C). The fish were offered three different diets: D1 ( Artemia nauplii), D2 ( Artemia nauplii + 50% dry feed) and D3 (dry feed). After a 21-day experiment, best results for growth and survival were obtained with diets D1 and D2 ( P P Artemia and mixed diets). The liver and hepatocyte structures of the larvae fed D1 and D2 diets showed no signs of anomaly, contrary to what was observed in D3-fed larvae (irregularly linked hepatocytes, numerous blood vessels, absence of Golgi apparatus but high lysosome number in the hepatocytes).

Effect of stocking density on the dynamics of cannibalism in sibling larvae of Perca fluviatilis under controlled conditions

The effect of stocking density (10, 31.6 and 100 larvae l 1 ; three replicates per treatment) on the day-by-day dynamics of survival, growth and cannibalism was examined in sibling perch larvae reared from eyed-egg stage in 100-l cages (16L:8D, 20.0F0.5 jC, O2z6.0 mg l 1 ; feeding in excess with live Artemia nauplii during the photophase) during the first 3 weeks of exogenous feeding. Larvae unable to achieve the transition to exogenous feeding died in between 7 and 11 days post-hatch. Later, mortality from causes other than cannibalism never exceeded 1% day 1 . Cannibalism did not start before days 10–11 and first consisted in the incomplete ingestion of prey attacked tail first, exclusively. This type of cannibalism never caused losses higher than 2.0% of the initial stock, and ceased after days 16–18. From days 12–14 onwards, differential growth was apparent, and cannibals turned to complete cannibalism of small prey ingested head first, which caused greater losses (28–53% of the stock). Increasing the stocking density did not compromise growth and decreased the overall impact of cannibalism through several complementary mechanisms: (i) a postponed emergence of cannibalism, (ii) a lower proportion of cannibals in the population, and (iii) probably a lower rate of cannibalism per capita as predation was complicated and less directed at high stocking density. D 2003 Elsevier Science B.V. All rights reserved.

Growth and nutritional status of Eurasian perch Perca fluviatilis fed graded levels of dietary lipids with or without added ethoxyquin.

Abstract An 8-week experiment was conducted to establish the optimal dietary lipid levels in relation to feed intake, growth rate, lipid storage and nutritional status of juvenile Eurasian perch. All diets contained 40% crude protein and graded levels (ranging from 6% to 18%) of stabilized (addition of ethoxyquin as antioxidant) or unstabilized (no addition of ethoxyquin) menhaden oil as lipid source. Feed intake was high in all groups fed diets containing stabilized lipid and intermediate in fish fed 6% dietary lipid without ethoxyquin. On the other hand, feed intake was significantly lower in fish fed 12% and 18% unstabilized dietary lipid but increased during the experiment, indicating an habituation of perch to accept oxidised lipid diets. Dietary lipid concentrations and addition of ethoxyquin significantly influenced weight gain and feed efficiency, the best results being obtained at 12% and 18% stabilized lipid, while the poorest growth was recorded at high concentration of unstabilized lipids (18%). Fatty acid composition of perch tissues (muscle, viscera and liver) was significantly affected by the dietary treatments. At 12% and 18% dietary lipid, the addition of ethoxyquin significantly increased the total polyunsaturated fatty acid concentration in perch liver and muscle as well as the n−3/n−6 ratio. Concentrations of linolenic, eicosapentaenoic and docosapentaenoic acids were low in fish fed unstabilized lipid diets while docosahexaenoic acid was not influenced by the absence of ethoxyquin. Ultrastructure observations revealed noticeable modifications in the hepatocytes of fish fed high lipid diets, with a large accumulation of lipid droplets in the cytoplasm and a marked reduction of mitochondria and rough endoplasmic reticulum.

Reproductive cycle and plasma levels of sex steroids in female Eurasian perch Perca fluviatilis

Abstract From April 1995 to April 1996, the annual reproductive cycle of the Eurasian perch Perca fluviatilis was studied at the Fishfarming Lindre Center (Moselle, France). At monthly intervals (at intervals of 10 days during the periovulatory period), 5 females were caught and dissected. From sampled organs, the gonado-, hepato- and viscerosomatic indexes (GSI, HSI, VSI) were calculated, oocyte diameters (OD) and the plasma levels of testosterone (T), 17β-estradiol (E 2 ), 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and protein-phosphorus (PPP) were measured. After the sexual resting period observed from May to August (GSI 2 , 17,20β-P and PPP were low during the sexual resting period. E 2 and PPP levels increased significantly at the onset of the oogenesis in September, then the E 2 level raised abruptly in November (3–4 ng · mL −1 ). In December, the T level increased rapidly to 15–20 ng · mL −1 . The testosterone, E 2 and PPP levels remained very high until spawning, indicating the existence of active vitellogenesis. The highest HSI (2.1–2.2 %) recorded in winter confirmed this. During the periovulatory period, a peak of E 2 (4 ng · mL −1 ) appeared, whereas T level diminished. In this study, 17,20β-P levels remained low (0.2–0.6 ng · mL −1 ) and relatively constant. No 17,20β-P peak was observed during the periovulatory period. Sampling at 10 day intervals was probably inadequate to specify the hormonal variations related to the final oocyte maturation and the ovulation.