Effect of arsenic and cyanobacterial co-exposure on pathological, haematological and immunological parameters of rainbow trout (Oncorhynchus mykiss).

OBJECTIVES: Under environmental conditions, fish are simultaneously exposed to multiple stressors. This study provides new knowledge on the effects of controlled exposure to multiple stressors, namely cyanobacterial biomass and food contaminated with arsenic. METHODS: Rainbow trout were divided into six groups of 25 fish and exposed to different contaminant combinations for 30 days: 1) control group, 2) cyanobacterial biomass, 3 & 4) two groups exposed to arsenic at concentrations of 5 mg.kg(-1) and 50 mg.kg(-1) fish feed, and 5 & 6) two groups exposed to cyanobacterial biomass and arsenic combined. We then evaluated pathological, haematological and immunological parameters at 10, 20 and 30 days after exposure. RESULTS: Marked gross pathological findings were present in groups exposed to arsenic and arsenic/cyanobacteria after 30 days. A strong decrease in haemoglobin concentration was observed in all experimental groups receiving arsenic after 10 days exposure. Total leukocyte count increased markedly in fish exposed to cyanobacterial biomass, and to higher arsenic concentrations by the end of the experiment. Neutrophils decreased significantly at the end of exposure. Similarly, exposure to cyanobacteria and/or arsenic led to suppression of opsonised zymosan particle-induced neutrophil respiratory bursts. CONCLUSIONS: Our results demonstrate that the effects of exposure to toxic cyanobacterial biomass and arsenic on fish are enhanced when the contaminants are combined. In particular, long-term exposure led to disturbances in the white blood-cell count. Modulation of phagocytosis, which is the first line of defence against invading pathogens, suggests that the combined action leads to a decreased ability to control infection.

Combined exposure of carps (Cyprinus carpio L.) to cyanobacterial biomass and white spot disease.

OBJECTIVES: Under environmental conditions, fish can be exposed to multiple stressors including natural toxins and infectious agents at the same time. This study brings new knowledge on the effects of controlled exposure to multiple stressors in fish. The aim of this study was to test the hypothesis that influence of cyanobacterial biomass and an infection agent represented by the white spot disease can combine to enhance the effects on fish. METHODS: Common carps were divided into four groups, each with 40 specimens for 20 days: control group, cyanobacterial biomass exposed group, Ichthyophthirius multifiliis-infected fish (Ich) and cyanobacterial biomass-exposed fish + Ichthyophthirius multifiliis-infected fish. During the experiment we evaluated the clinical signs, mortality, selected haematological parameters, immune parameters and toxin accumulation. RESULTS: There was no mortality in control fish and cyanobacterial biomass-exposed fish. One specimen died in Ichthyophthirius multifiliis-infected fish and the combined exposure resulted in the death of 13 specimens. The whole leukocyte counts (WBC) of the control group did not show any significant differences. Cyanobacteria alone caused a significant increase of the WBC on day 13 (p≤0.05) and on day 20 (p≤0.01). Also, I. multifiliis caused a significant elevation of WBC (p≤0.01) on day 20. Co-exposition resulted in WBC increased on day 13 and decrease on day 20, but the changes were not significant. It is evident from the differential leukocyte counts that while the increase of WBC in the group exposed to cyanobacteria was caused by elevation of lymphocytes, the increase in the group infected by I. multifiliis was due to the increase of myeloid cells. It well corresponds with the integral of chemiluminescence in the group infected by I. multifiliis, which is significantly elevated on day 20 in comparison with all other groups. CONCLUSIONS: We can confirm additive action of different agents on the immune system of fish. While single agents seemed to stimulate the immune response, the combination of both caused immunosuppression.

Influence of cyanobacteria on water activity and dry matter of muscles in the common carp (Cyprinus carpio L.) and rainbow trout (Oncorhynchus mykiss W.).

OBJECTIVES: Cyanobacteria are studied from the viewpoint of the issue of risks to water supply, agriculture and recreational activities for a long time. Cyanobacteria produce a wide range of substances which can be toxic and can influence the safety and quality of fish products. The aim of this study was to determine whether the diet with the content of cyanobacteria can affect the water activity and the dry matter of fish muscle and whether this diet can contribute significantly to the shelf life of fish muscles. METHODS: Common carp (Cyprinus carpio) and rainbow trout (Oncorhynchus mykiss) were used in this study. Both fish species were divided into two groups. The first group of fish was fed with feed with cyanobacteria (3% of dry matter), the second group with feed without cyanobacteria. The water activity and the dry matter were monitored immediately after sampling of the fish muscle on day 7, 14 and 21 (carp) or on day 10, 20 and 30 (rainbow trout) and seven days after every sampling and cold storage (6-8 °C). RESULTS: Feed with the content of cyanobacteria significantly decreased the water activity in muscles of both fish species on day 21 (in carp) and on day 30 (in rainbow trout). The dry matter of fish muscle significantly increased on day 7 and 21 (in carp) and on day 10 and 30, but decreased on day 20 (in rainbow trout). The cold storage significantly influenced the dry matter only. While the dry matter was increased in the common carp (7 days of cold storage after sampling on days 14 and 21), the dry matter decreased in the rainbow trout (7 days of cold storage after sampling on day 10). CONCLUSIONS: The decrease of water activity was found only after longer exposure in the both exposed fish species. The dry matter was influenced far greater and was mostly increased in the both exposed fish species.