Using of natural plants as immunostimulant in fish is more useful than antibacterial drugs that cause adversely side effects for fish, environment and consumers. Therefore, we investigated the effect of black cumin seeds, Nigella sativa, as a herbal medicine plant on some immuno-hematological parameters and specific as well as non-specific defence mechanisms of rainbow trout, Oncorhynchus mykiss. Fish were fed with basal diet incorporated with 1, 2.5 and 5% Nigella sativa for 21 days. At the end of experiment, the hematocrit (Hct), leukocyte levels, glass-adherent NBT positive cell activation, serum protein and total immunoglobulin level were determined in fish blood. No significant differences (P >0.05) were found in hematocrit levels of fish fed the diets containing 1 and 2.5% black cumin seeds, but it was significantly (P <0.05) increased in fish receiving diet containing 5% black cumin seeds compared to the control. Glass-adherent NBT positive cell activation and leukocyte level in black cumin supplemented groups showed no significant differences (P >0.05) when compared to the control group. The serum protein and total immunoglobulin levels were significantly (P <0.05) higher than those of the control group. In conclusion, based on the current findings together with the low cost and the immunostimulative effect of black cumin seed, it is recommended to be used in fish feed to minimize the mortalities caused by some pathogens.

Three sympatric morphs of Arctic charr Sulvelinus alpinus occur in Loch Rannoch, Scotland, and are identified by their differing head morphology and diet. These are small-headed benthic, large-headed benthic and pelagic morphs. Six species of endoparasitic helminth were found in the fish, but the morphs had different patterns of infection. Overall infections in pelagic charr were heavier than in large-headed benthics, which were in turn heavier than in small-headed benthics, even though benthic charr live longer than pelagics. Pelagic fish had high prevalences and intensities of pseudophyllidean tapeworms, the intermediate hosts of which are copepods. The prevalence and intensity of metacercariae of Diplostomurn sp. (the intermediate hosts of which are snails) were high in the benthic morphs. The results are discussed in terms of the effects of ecological factors on transmission of helminth parasites to their hosts and the evolution of host-parasite associations. f:, 1995 The Fisheries Society of the British Isles

In this study, the toxic effects on the embryos and larvae of the common carp were used as a model to investigate the synthetic pyrethroid pesticide, cypermethrin, which contaminates aquatic ecosystems. Data obtained from the cypermethrin acute toxicity tests were evaluated using the Probit Analysis Statistical Method. The control and eight test experiments were repeated five times. The number of dead embryos significantly increased in response to cypermethrin concentrations 0.0001, 0.001, 0.01, 0.1, 1, 2, 4 and 8 lg l À1 (p<0.05 for each case). The 48 h LC 50 value (with 95% confidence limits) of cypermethrin for common carp embryos was estimated at 0.909 (0.256-5.074) lg l À1 . Dose-response decreases in hatching success were recorded as 87.4, 85.0, 80.2, 71.4, 56.3, 48.6, 38.8 and 23.5%, respectively. The lowest concentration of cypermethrin (0.0001 lg l À1 ) produced a significant increase in the number of dead larvae compared to the control group (p<0.05). The number of dead larvae significantly increased with increasing cypermethrin concentrations exposed for 1-96 h (p<0.05). The highest concentration (8 lg l À1 ) showed the highest larvae mortality. The 96 h LC 50 value (with 95% confidence limits) of cypermethrin for common carp larvae was estimated at 0.809 (0.530-1.308) lg l À1 . The results of the study suggest that low levels of cypermethrin in the aquatic environment may have a significant effect on the reproduction and development of carp.

In this study, we recovered Schistocephalus solidus plerocercoids from singly and multiply infected three-spine sticklebacks, Gasterosteus aculeatus, transferred them individually to in vitro culture conditions, and quantified their lifetime egg output. We found a significant difference in the relationships between plerocercoid mass and lifetime egg output for parasites recovered from singly and multiply infected sticklebacks. Although egg output was strongly and positively related to plerocercoid mass amongst worms from singly infected fish, for those recovered from multiply infected sticklebacks the relationship was marginally nonsignificant and negative, with small worms achieving high levels of egg production. We suggest 2 hypotheses that may explain differences in the egg production of plerocercoids from singly and multiply infected fish. One possibility is that smaller plerocercoids in asymmetric multiple infections develop precocially, in response to host manipulation strategies of larger worms that decrease survival prospects of the host. Alternatively, small worms in singly infected sticklebacks may be prevented from becoming sexually mature because they face energetic constraints associated with having to overcome the host's immune response alone. We discuss our results in terms of recent studies examining strategic egg production in helminths.

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