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.

Experimental assessment of the probabilistic maturation reaction norm: condition matters.

The probabilistic maturation reaction norm (PMRN) describes an individual's probability of maturing at a given age as a function of size and other relevant phenotypic traits. Population-level shifts in the PMRN are often interpreted to indicate genetic as opposed to phenotypic changes in maturation in fish. Inferences derived from trends in the PMRN have been challenged, warranting an experimental assessment of the method. This was accomplished in a laboratory experiment using zebrafish (Danio rerio). Fish were reared under different food levels to induce variation in growth and maturation. Plasticity in maturation was not entirely captured by the demographic age- and length-based PMRN. Adding condition to the PMRN captured a greater amount of environmental variation in maturation probability. Nevertheless, significant differences in the PMRNs among the food levels remained after accounting for the influences of age, size and condition on maturation probability indicating plasticity of the PMRN. This was particularly pronounced between fish held on low food levels as compared with fish experiencing abundant resources, with the latter experiencing higher size-specific maturation probabilities. Our analysis emphasizes the need for incorporating salient physiological traits influencing maturation, such as condition, to make accurate inferences about documented shifts observed in the position of PMRNs on maturation trends in wild fish stocks.

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.

Toxicity of peracetic acid (PAA) to tomonts of IIchthyophthirius 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.

Effects of cadmium exposure on embryogenesis of Stagnicola elodes (Mollusca, Gastropoda): potential consequences for parasite transmission.

Experiments on the toxicity of cadmium (Cd(2+)) 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 Cd(2+)/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 Cd(2+)/L, 3.9 (+/- 0.7) at 0.2 mg Cd(2+)/L, and 1.1 (+/- 0.08) at 2.0 mg Cd(2+)/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 Cd(2+)/L exhibited a prolonged gastrula period and failed to hatch. Eggs in the 0.2 mg Cd(2+)/L group were blocked in the gastrula stage on day 5, whereas individuals exposed to 2.0 mg Cd(2+)/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 >or=0.02 mg Cd(2+)/L will thus decrease transmission success of various trematodes by decreasing intermediate host snail abundance.

[Antiparasitic effects of peracetic acid (PAA) against infective stages (theronts) of white spot disease, Ichthyophthirius multifiliis in vitro]. / Antiparasitäre Effekte von Peressigsäure (PES) gegen infektiöse Stadien (Theronten) der Weisspünktchenkrankheit, Ichthyophthirius multifiliis in vitro.

White spot disease, caused by the protozoan parasite Ichthyophthirius multifiliis (I. multifiliis), invades nearly all fresh water fish species and causes huge economic losses. In Germany no protocide substance is legal for the treatment of I. multifilis. As an alternative substance the peracetic acid (PAA) was tested to treat the free invasive stage (theront) of the parasite. PAA concentrations of 0.3 ppm were able to kill all theronts in 120 min in our investigations. As a result of these investigations we recommend an interval-application of 0.3 to 0.5 ppm PAA for 30 to 150 min. This application should be prolonged for two life cycles of the parasite. Biotic parameters as e. g. fish species, and age as well as abiotic parameters as e. g. temperature, pH and organic load of the water could possibly influence the efficiency of the PAA application and should therefore be taken into account while picking the dosage and length of the PAA exposure.

[Application of peracetic acid for the treatment of juvenile sander (Sander lucioperca) during Ichthyophthirius multifiliis infestation]. / Einsatz von Peressigsäure zur Behandlung juveniler Zander (Sander lucioperca) bei Ichthyophthirius-multifiliis-Befall.

White spot disease caused by the ciliate protozoan parasite Ichthyophthirius multifiliis (I. m.), is one of the most dangerous diseases in aquaculture and ornamental fish breeding worldwide. The parasite is characterized by three developmental stages: a reproductive tomont, an infective theront and a parasitic trophont. In sander (Sander lucioperca) breeding I. m. causes serious economic losses. After banning of the traditional therapeutic agent malachite green we have to face a state of emergency for the treatment of the ichthyophthiriasis in Germany. The peracetic acid (PAA), characterized by positive therapeutical properties, might close this gap. The purpose of our investigations was the determination of the toxicity of PES to juvenile sander as well as the evaluation of the therapeutic effectiveness of the substance to combat I. m. For juvenile sander (length 3 cm) we determined a 24-h-LC50 of 1.14 (0.97; 1.3) ppm PES. In two investigations PAA was applied in daily intervals of 0.5; 1, 3, 5 and 24 h and concentrations of 0.5; 1; 1.5 and 2 ppm to treat I.-m.-infection in sander. In test I all sander (length 9 cm) died as a result of the I.-m.-infection. However, the PAA exposed fish survived longer than the PES-free controls! This might be due to a disinfection of other pathogens by PAA. In test II, the fish (length 12 cm) were less infected than fish in test I. Four of six fish died in the group exposed with 2 ppm PAA for 24 hours. The abundance of I.-m.-trophonts was determined in mucus, fin and gill tissues of all fish. Significant differences could not be observed between test I and test II because of dissimilar: 1. exposure in time and concentration, 2. age and condition of the fish and 3. homogenity of the variances. Therefore, no therapy strategy was successful while fighting the parasitic trophonts protected by the overlaying fish tissues. We speculate that a successful therapy of I. m. with PAA is, as known e.g. for malachite green, only possible while fighting the free living stages theronts and tomonts. This will be part of our subsequent investigations.

Dynamics of Anguillicola crassus larval infections in a paratenic host, the ruffe (Gymnocephalus cernuus) from the Oder River on the border of Germany and Poland.

The course of infection of 2-year-old ruffe (Gymnocephalus cernuus L.) from the Oder River (Germany/Poland) with third-stage larvae (L3) of Anguillicola crassus (Nematoda: Anguillicolidae) was investigated at monthly intervals between March 1994 and March 1995. Of 230 fish examined, 152 (66%) harboured viable L3. Monthly prevalences fluctuated between 12 and 96%; mean intensities ranged from 1.0 to 5.6 L3 per infected fish. Temperature-dependent differences in infection were noted with the prevalence and mean intensity of infection being significantly higher (Chi-Square test and Mann-Whitney-U-test, respectively; ) at water temperatures less than 10 degrees C (cold period) than at those above (warm period). These differences remained significant even after the division of fish samples into two size classes (8.5-10.5 cm, 11-13 cm). Although the paratenic hosts may acquire infections year round, the results suggest that ruffe become infected mainly during the cold season and that the host's feeding ecology determines the final course of infection.

Effects of mercury and chromium upon longevity of Diplostomum sp. (Trematoda: Diplostomidae) cercariae.

Laboratory experiments were carried out to examine the impact of mercury and chromium upon survival of Diplostomum sp. cercariae. Freshly emerged cercariae were exposed to solutions of either mercury, at concentrations ranging between 0.1 and 100 microg/l, or chromium at concentrations from 2 microg/l to 2 mg/l. The mortality patterns and mean survival times (MSTs) of the exposed parasites were determined by the Kaplan-Meier estimator and were compared (log-rank test) with corresponding patterns and estimators of the unexposed controls. Mercury concentrations > or = 10 microg/l caused statistically significant changes in the mortality pattern of Diplostomum sp. cercariae and reduced MST by at least 9 h compared with the control group, in which MST was 42 h. Cercariae exposed to chromium solutions had statistically significant changes in mortality pattern only at a concentration of 2 mg/l and exhibited a reduction in MST of 8 h compared with the control (MST = 41 h). The results show for the first time that longevity of Diplostomum sp. cercariae can be reduced by direct exposure to heavy metals. Ecotoxicological effects of mercury are manifested at lower concentrations than those of chromium, and thus potentially have a higher impact on parasite populations and communities.

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.

Influence of aqueous sediment extracts from the Oder River (Germany/Poland) on survival of Diplostomum sp. (Trematoda: Diplostomidae) cercariae.

Laboratory experiments were carried out to test whether the life span of Diplostomum sp. cercariae is affected by contamination of its aquatic environment. Freshly emerged cercariae therefore were exposed to either standardized water, Oder River (Germany/Poland) or Lake Odersee (Germany) extracts of aqueous sediments; mortality patterns and mean survival times (MSTs) were compared. Cercariae added to extracts of aqueous sediments from the Oder River and Lake Odersee exhibited impaired survival with significantly different mortality pattern and reduced MST compared to that of controls. A significant negative correlation (r = -0.843, p < 0.05) was found between MST and mercury content of sediments, indicating a potential impact of mercury on survival of Diplostomum sp. cercariae. The results indicate that contamination of freshwater habitats may influence the viability of free-living transmission stages of helminth parasites of fish and may thus be of epizootiological significance.

Ecology of proteocephalus torulosus in the blue bream (Abramis ballerus) fromthe oder river on the borders of germany and poland

During studies on the ecology of fish helminths, the tapeworm Proteocephalus torulosus (Batsch, 1786) was frequently found in the intestine of the blue bream (Abramis ballerus) from the Oder River (Germany/Poland). In total, 633 fish, ranging between two and 16 years old, were sampled at monthly intervals over a two year period during 1993-1995. Statistically significant differences in the seasonal occurrence of the parasite in its fish host were observed. In 1993, the prevalence remained at a high level, ranging between 61. 9 and 100%. During the summer of 1994, this value decreased to 5.5% and remained low for the rest of the year. The pattern of mean intensity of infection was similar to that of the prevalence. In 1993, the mean intensity varied between 8.4 and 31.8 worms per infected fish, with a continual loss of worms being observed in the summer of 1994. Changes in the amount of suspended particulate matter in water have been identified as the main cause of these observed differences in the course of infection of blue bream.

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 < or = r < or = 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.