Thomas Meinelt

Interaction of cadmium toxicity in embryos and larvae of zebrafish (Danio rerio) with calcium and humic substances

The influence of humic substances (HS) and calcium (Ca) on cadmium (Cd) toxicity was determined using zebrafish (Danio rerio). Embryo and larvae of the zebrafish were exposed to various Cd concentrations (1.8; 2.8; 4.2; 6.2; 9.3 mg/l Cd) for 144 h. Combinations of low (0.2 mmol/l) and high (2 mmol/l) Ca, +HS (5 mg/l C) or -HS were used during Cd exposure. The toxicity of Cd was affected by (1) exposure concentration; (2) exposure time; (3) presence of HS; and (4) the Ca concentration. The results show that Ca and HS protect against Cd toxicity in zebrafish embryos. The best protection was in the high Ca-HS group, followed by high Ca+HS group and low Ca+HS group. The survival in the low Ca-HS group was the worse. Survival in the high Ca-HS group and the high Ca+HS group was similar with the exception of the highest Cd concentration (9.3 mg/l) where the survival of the high Ca+HS group was less than in the high Ca-HS group. The exposure system was modelled using a chemical equilibrium program (MINEQL+) to determine if the likely mechanism causing the anomalous result in the highest Cd concentration. The equilibrium model cannot explain these results, which suggests that this effect has a kinetic basis, such as time needed for Cd to displace Ca already bound by HS.

The evolutionary legacy of size-selective harvesting extends from genes to populations.

Size‐selective harvesting is assumed to alter life histories of exploited fish populations, thereby negatively affecting population productivity, recovery, and yield. However, demonstrating that fisheries‐induced phenotypic changes in the wild are at least partly genetically determined has proved notoriously difficult. Moreover, the population‐level consequences of fisheries‐induced evolution are still being controversially discussed. Using an experimental approach, we found that five generations of size‐selective harvesting altered the life histories and behavior, but not the metabolic rate, of wild‐origin zebrafish (Danio rerio). Fish adapted to high positively size selective fishing pressure invested more in reproduction, reached a smaller adult body size, and were less explorative and bold. Phenotypic changes seemed subtle but were accompanied by genetic changes in functional loci. Thus, our results provided unambiguous evidence for rapid, harvest‐induced phenotypic and evolutionary change when harvesting is intensive and size selective. According to a life‐history model, the observed life‐history changes elevated population growth rate in harvested conditions, but slowed population recovery under a simulated moratorium. Hence, the evolutionary legacy of size‐selective harvesting includes populations that are productive under exploited conditions, but selectively disadvantaged to cope with natural selection pressures that often favor large body size.

Mercury pollution and macrophage centres in pike (Esox lucius) tissues

From June 1993 to October 1994, studies have been carried out on the effects of mercury in the Oder River and pike tissue contamination (muscle, kidney, liver). The mean mercury contents in the sediment range from 0.03 to 1.1 mg/kg dry weight. In the pike muscle, between 0.22 and 0.85 mg/kg, on a wet weight basis, were found. The measured mercury concentrations were analysed in relation to the number of macrophage centres of the liver, spleen and kidney of the pike. Positive correlations between mercury and MC response (0.54 ≤ r ≤ 0.79, p < 0.05) were found in all of these organs. The suitability of the macrophage-centre-response as a possible bioindicator for mercury pollution is discussed in the literature. In our study, the response of MCs was found to be suitable as a biomarker for the impairment of fish health.

Humic substances affect physiological condition and sex ratio of swordtail (Xiphophorus helleri Heckel)

Abstract.Exposure of young swordtail (Xiphophorus helleri) to increasing concentrations of synthetic humic substances (HS1500) significantly effected the physiological condition and slightly effected the sex ratio of the fish. Any exposure enhanced the body mass development of the swordtail compared to the control. No dose-dependent effect of HS on growth was detectable. After a two-week period of stressful handling, the HS-exposed fish recovered quickly whereas growth stagnated in the control fish. The examination of gills, fins, and skins revealed no infestation with ectoparasites. We assume that the growth promoting effect of HS1500 was due to an overall stimulation in metabolism. Furthermore, the sex ratio of fish exposed to HS1500 for 21 weeks slightly shifted in favor of females in a dose-dependent manner. Although the mode of action is still obscure, there is a probability that alkylphenol structures in HS1500 may be responsible for this weak feminization.

Toxicity of peracetic acid (PAA) to tomonts of Ichthyophthirius multifiliis.

The free-living infective theront of Ichthyophthirius multifiliis historically has been thought to be the only stage susceptible to treatment. Here we introduce a technique to determine the toxicity of compounds to the newly released tomont, the encysted tomont and the developing tomites within the tomont that emerge as theronts. The toxicity of Wofasteril E400 (40% peracetic acid, PAA) to free-living forms of I. multifiliis was determined shortly after tomonts were physically removed from the surface of the fish and at 2.5 and 24 h after removal. Results indicate that 0.6 to 0.9 mg l(-1) PAA killed 39 to 82% of the newly released tomonts within 48 h when treated immediately. In a second experiment, tomonts were allowed to settle for 2.5 h after sampling from the skin and then treated for 12 h; concentrations > or =0.5 mg l(-1) PAA produced significantly fewer theronts than the controls. In a third experiment, encysted tomonts that were exposed to PAA 24 h after sampling from the skin and treated for 2 or 4 h produced a variable amount of theronts, but the concentrations tested (0.5 to 3.0 mg l(-1)) did not halt theront production. This research demonstrates that encysted I. multifiliis are less susceptible to chemical treatments.

Size-dependent reproductive success of wild zebrafish Danio rerio in the laboratory

Size-dependent reproductive success of wild zebrafish Danio rerio was studied under controlled conditions in the laboratory to further understand the influence of spawner body size on reproductive output and egg and larval traits. Three different spawner size categories attained by size-selective harvesting of the F(1)-offspring of wild D. rerio were established and their reproductive performance compared during a 5 day period. As to be expected, large females spawned more frequently and had significantly greater clutch sizes than small females. Contrary to expectations, small females produced larger eggs when measured as egg diameter with similar amounts of yolk compared to eggs spawned by large spawners. Eggs from small fish, however, suffered from higher egg mortality than the eggs of large individuals. Embryos from small-sized spawners also hatched later than offspring from eggs laid by large females. Larval standard length (L(S))-at-hatch did not differ between the size categories, but the offspring of the large fish had significantly larger area-at-hatch and greater yolk-sac volume indicating better condition. Offspring growth rates were generally similar between offspring from all size categories, but they were significantly higher for offspring spawned by small females in terms of L(S) between days 60 and 90 post-fertilization. Despite temporarily higher growth rates among the small fish offspring, the smaller energy reserves at hatching translated into lower condition later in ontogeny. It appeared that the influence of spawner body size on egg and larval traits was relatively pronounced early in development and seemed to remain in terms of condition, but not in growth, after the onset of exogenous feeding. Further studies are needed to explore the mechanisms behind the differences in offspring quality between large- and small-sized spawners by disentangling size-dependent maternal and paternal effects on reproductive variables in D. rerio.

Peracetic acid is effective for controlling fungus on channel catfish eggs.

Peracetic acid (PAA) is a relatively new compound suggested for use to treat pathogens in aquaculture. It is approved for use in Europe, but not in the United States. This study determined the effectiveness of PAA for fungus control on channel catfish, Ictalurus punctatus (Rafinesque), eggs. The study consisted of five PAA concentrations (2.5, 5, 10, 15 and 20mgL(-1) ) and an untreated control in a flow-through system. A single spawn was used for each replication (N =4). Eggs were treated twice daily until the embryos developed eyes. When hatching was complete for all viable eggs, fry were counted to determine the percent survival in each treatment. Fungal growth was severe in the untreated controls resulting in 11% survival. Treatments of 2.5, 5 and 10mgL(-1) PAA were significantly different from the controls (P<0.05). The highest percent survival of hatched fry was with 5mgL(-1) PAA administered twice daily; the 2.5mgL(-1) PAA treatment had slightly less survival, but gives a higher margin of safety in case of treatment error. Very little fungus was present in treatments receiving 2.5mgL(-1) PAA or higher, and concentrations of 15 and 20mgL(-1) PAA were toxic to the eggs. The mean survivals in the 0, 2.5, 5, 10, 15 and 20mgL(-1) PAA treatments were 11%, 60%, 63%, 62%, 32% and 0%, respectively. Therefore, PAA may be a compound that merits further investigations regarding its use in U.S. aquaculture.

Effects of Cadmium Exposure on Embryogenesis of Stagnicola elodes (Mollusca, Gastropoda): Potential Consequences for Parasite Transmission

Experiments on the toxicity of cadmium (Cd2+) to the embryonic development of Stagnicola elodes (Mollusca, Gastropoda), obligatory first intermediate host of numerous trematodes of pathogenic importance, were carried out as part of a study on the effects of metal pollution on host-parasite relationships. Freshly laid snail eggs were exposed to Cd concentrations of 0, 0.02, 0.2, and 2.0 mg Cd2+/L, and survival and embryogenesis were examined for 30 days. Mean survival time (± SD) of the control group was 23.1 (± 5.3) days compared with 10.1 (± 3.2) at 0.02 mg Cd2+/L, 3.9 (± 0.7) at 0.2 mg Cd2+/L, and 1.1 (± 0.08) at 2.0 mg Cd2+/L. Mortality patterns of all test groups differed significantly from each other, demonstrating that the percentage of surviving individuals at any given time was inversely related to Cd concentration. Concentration-dependent effects of Cd exposure on snail embryogenesis were noted. While embryos of the control group developed properly and started hatching on day 16, eggs exposed to 0.02 mg Cd2+/L exhibited a prolonged gastrula period and failed to hatch. Eggs in the 0.2 mg Cd2+/L group were blocked in the gastrula stage on day 5, whereas individuals exposed to 2.0 mg Cd2+/L died in the morula stage on the second day. Data showed that Cd severely affects S. elodes embryogenesis. By implication, Cd contamination at concentrations ≥0.02 mg Cd2+/L will thus decrease transmission success of various trematodes by decreasing intermediate host snail abundance.

Paternal body size affects reproductive success in laboratory-held zebrafish (Danio rerio)

Across many fish species, large females tend to exhibit higher individual reproductive success due to elevated fecundity and the provisioning of better conditioned eggs and offspring compared to small females. By contrast, effects of paternal body size on reproductive success are less well understood. We disentangled the maternal- and paternal-size dependent effects on reproductive output and early life history in zebrafish (Danio rerio). In the laboratory, females and males from four size categories (small, medium-sized, large and very large) were allowed to spawn freely in a full factorial design with 10 replicates per size combination. As expected, larger females produced more eggs and better conditioned offspring compared to smaller females. Male body size further contributed to zebrafish reproductive success: offspring sired by large males exhibited higher hatching probability and these offspring also hatched earlier and larger than offspring fertilized by small males. However, the largest males experienced lower mating success and received fewer eggs than males of the smaller size classes. While male body size substantially affected reproductive success in zebrafish, it remained unclear whether and to what degree direct paternal effects (e.g., related to sperm quality) or indirect paternal effects stemming from differential allocation patterns by females were the mechanism behind our findings. Answering this question constitutes an important future research topic.

Veränderung der Zinktoxizität in Wässern geringer und hoher Wasserhärte unter dem Einfluß eines synthetischen Huminstoffes

ZusammenfassungIm Ei-Brut-Test mit Zebrabärblinge wurde die Wechselwirkung von Zink mit einem Huminstoff (HS) bei unterschiedlichen Wasserhärten untersucht. In weichem ungepuffertem Wasser reduziert sich die Toxizität von Zink durch die Zugabe von 5 mg HS/l extrem. Eine Nutzung von HS als Antidot bei Anwesenheit Fische gefärdender Zinkkonzentrationen in weichem Wasser ist somit möglich. In hartem Wasser vermag der Huminstoff durch Wechselwirkung mit den Härtebildnern seine entgiftende Wirkung und den protektiven Effekt hoher Wasserhärten gegen Schwermetalle durch Bindung härtebildender Ionen (Ca2+, Mg2+) an die Huminsäuren zu verändern. Die Toxizität von Zink gegen Embryonon und Larven des Zebrabärblings wurde dabei erhöht.AbstractIn soft water 5mg/l of a synthetic dissolved humic substance (HS) reduced the toxicity of zinc against zebrafish embryo and larvae. The appliation of this HS as an antidot against fish hazardous zinc concentrations particulary in soft water is possible. In hard water the HS is able to change the detoxification effect of high water hardness because of the interaction between the calcium and magnesium ions and the HS. In this case the protective effect of high water hardness against trace metals is reduced because of the adhesion of hardness producing ions (Ca2+, Mg2+) with the HS.