Influence of arsenic and cyanobacteria co-exposure on plasmatic parameters of rainbow trout (Oncorhynchus mykiss W.).

OBJECTIVES: Fish can be exposed under environmental conditions to multiple stressors including natural toxins and environmental or feed contamination at the same time. This study brings new knowledge about 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 arsenic in feed can combine to enhance the effects on fish. METHODS: Rainbow trouts were sorted into six groups, each with 25 specimens: control group (fed with commercial feed), groups exposed to toxic cyanobacterial biomass (81 mg x kg(-1) MCs of feed), two groups exposed to arsenic (concentration of 5 mg x kg(-1), and 50 mg x kg(-1) of fish feed) and two groups exposed to combination of cyanobacterial biomass and arsenic in two concentrations mentioned above. The experiment lasted 30 days. During the experiment we evaluated the influence of co-exposure on plasmatic parameters mentioned above. Samples were collected on days 10, 20 and 30 of exposure. RESULTS: Biochemical analysis revealed a significant decrease in calcium (T20) and an increase in natrium (T10) and chlorides (T10) values in combined cyanobacterial and arsenic exposures. Our results showed a significant decrease in the values of magnesium after exposure to higher concentration of arsenic compared to control and feeding with addition of cyanobacterial biomass groups. The changes of other monitored plasmatic parameters were not significantly increased or decreased in comparison with controls. CONCLUSIONS: Our results confirmed the hypothesis that influence of toxic cyanobacterial biomass and a chemical agent represented by arsenic can combine to enhance the effects on fish. This work originally shows that while the single agents in sub-lethal doses do not cause changes in the plasmatic parameters, their co-exposure leads to the significantly decrease or increase of the electrolytes of rainbow trout.

Fish tapeworm Khawia sinensis: an indicator of environmental microcystins?

OBJECTIVES: Parasites have recently been recognized as accumulation indicators that take up and bio-concentrate substances from environmental pollution. Interestingly, helminths of fish are known to accumulate metals from the ambient environment and to contain several orders of magnitude higher concentrations than hosts. While the majority of reports mention inorganic toxin accumulation in parasites, studies concerning effects of organic pollution are infrequent and little is known about the potential of parasites to bio-accumulate microcystins. METHODS: The parasite-host system of tapeworm Khawia sinensis and common carp (Cyprinus carpio) was used to address this issue. Both the tapeworms and livers were dissected from experimental carps orally exposed to cyanobacterial biomass for 20 days. The total dose of microcystins amounted to 27 mg/kg of feed, i.e., 0.4 mg/kg of fish mass a day. Microcystin concentrations in tapeworms and carp liver tissues were measured using the LC-MS/MS method. RESULTS: Considering the three measured microcystin variants LR, YR and RR, only MC-RR was detected and its concentrations in tapeworms and carp liver tissue amounted to 5.78±3.78 ng/g and 2.11±0.74 ng/g fresh weight (p<0.05), respectively. CONCLUSIONS: Here we show accumulation of microcystin MC-RR in the tapeworm Khawia sinensis, a parasite of common carp (Cyprinus carpio). As this is the first report addressing this issue, further studies will be necessary to examine this specific parasite-host system.