ABSTRACT:This review summarizes the current knowledge on the contribution of metals to the development of oxidative stress in fish. Metals are important inducers of oxidative stress in aquatic organisms, promoting formation of reactive oxygen species through two mechanisms. Redox active metals generate reactive oxygen species through redox cycling, while metals without redox potential impair antioxidant defences, especially that of thiol-containing antioxidants and enzymes. Elevated levels of reactive oxygen species lead to oxidative damage including lipid peroxidation, protein and DNA oxidation, and enzyme inactivation. Antioxidant defences include the enzyme system and low molecular weight antioxidants. Metal-binding proteins, such as ferritin, ceruloplasmin and metallothioneins, have special functions in the detoxification of toxic metals and also play a role in the metabolism and homeostasis of essential metals. Recent studies of metallothioneins as biomarkers indicate that quantitative analysis of mRNA expression of metallothionein genes can be appropriate in cases with elevated levels of metals and no evidence of oxidative damage in fish tissue. Components of the antioxidant defence are used as biochemical markers of oxidative stress. These markers may be manifested differently in the field than in results found in laboratory studies. A complex approach should be taken in field studies of metal contamination of the aquatic environment. Keywords: ROS; metallothioneins; glutathion; superoxide dismutase; antioxidant defenceList of abbreviations ALA-D = aminolevulinic acid dehydratase; BNF = β-naphthoflavone; CAT = catalase; GPx = glutathione peroxidise; GR = glutathione reductase; GSH = glutathione; GSSG = glutathione disulphide; GST = glutathione S-transferase; LPO = lipid peroxidation; MDA = malondialdehyde; MTs = metallothioneins; NADPH = nicotinamidadeninedinucleotide phosphate (reduced); ROS = reactive oxygen species; SOD = superoxide dismutase

Stress load on harvest‐size common carp (Cyprinus carpio L.) just before harvest, during harvest and during the post‐harvest storage were assessed using haematological and biochemical indices. The study was carried out at the 60 ha Dřemliny pond for 28, 7 and 1 day before harvest, during 3‐day harvest and after a 28‐day post‐harvest period. Indices monitored included the relative spleen weight (SSI), erythrocyte count (Er), haemoglobin levels (Hb), haematocrit (PCV), MCV, MCH, MCHC, leucocrit (Bc), differential leucocyte count (leucogram), blood plasma cortisol, glucose, total proteins (TP), cholesterol and chloride. During harvest, a significant decrease of SSI (P<0.05; P<0.01), increase of PCV (P<0.01), decrease of Bc (P<0.01, P<0.05), lymphopenia (P<0.05) and neutrophilia (P<0.01) were observed. A significant increase in the levels of blood plasma cortisol was found 1 day before harvest (P<0.05) due to draining off the pond before harvest itself, hyperglycaemia was observed 1 day before harvest (P<0.05) and during harvest (P<0.01); a decrease, on the other hand, was found in cholesterol and chloride levels (P<0.01). The relationships between oxygen content in water and SSI and MCHC were positive (P>0.05) and between oxygen and glucose were negative (P>0.01). A 28‐day post‐harvest storage returned the indices investigated back to physiological interval of values. Persistently lower levels of Bc, lymphopenia, neutrophilia and lower TP concentrations are indicative of deepening immunosuppression during the post‐harvest storage period. Changes of haematological and biochemical indices during harvest in relation to hypoxia, fish handling and higher stocking rates are also discussed.

As the use of ingredients of plant origin has increased in aquaculture, the potential for mycotoxin poisoning in fish has increased accordingly. Feeding fish with mycotoxin‐contaminated feed can lead to a breakdown in health, manifested as tissue damage or through immunosuppression. Both effects can lead to an increase in mortality. To date, however, there have been few reports of mycotoxins in feed at toxic concentrations. The aim of this study was to describe the effects of those toxic mycotoxins most commonly found as contaminants in fish feed. In terms of fish health, the most harmful mycotoxins are aflatoxin B1 and Fusarium mycotoxins. The most sensitive fish species was rainbow trout, Oncorhynchus mykiss. Future research in the field of mycotoxicosis in fish should be focused on the effects of combinations of mycotoxins.

The aim of study was to evaluate the effect of atrazine exposure (5, 15, 20, and 30 mg·L−1) on common carp and the ability of regeneration. During 96 h exposure we observed abnormal behavior in fish exposed to 20 and 30 mg·L−1. Mortality and histological alterations were noticed only in the group exposed to 30 mg·L−1. Most experimental groups showed significantly (P < 0.05) lower values of haemoglobin, haematocrit, leukocyte, and lymphocyte and significantly higher values of monocytes, segmented and band neutrophile granulocytes, and also metamyelocytes and myelocytes. A significantly lower (P < 0.05) leukocyte count was also recorded in experimental groups (5 and 15 mg·L−1) after recovery period. Statistically significant (P < 0.05) alterations in glucose, total protein, lactate, phosphorus, calcium, and biopterin as well as in activities of ALT, AST, ALP, and LDH were found in most experimental groups. These changes were most apparent in the groups exposed to 20 and 30 mg·L−1. Most of the indices were found to be restored after the 7-day recovery period with the exception of LDH, ALT, and lactate in the group exposed to 15 mg·L−1. Our results showed that atrazine exposure had a profound negative influence on selected indices and also on histological changes of common carp.

ABSTRACT:The presence of mycobacteria was studied in Bull Rock Cave ("Byci skala") and the water catchment area of Jedovnice Brook ("Jedovnicky potok") using direct microscopy after Ziehl-Neelsen (ZN) staining, culture examination and molecular techniques. Mycobacteria were detected in 47.1% of a total of 68 samples. The mycobacterial genes hsp65 and dnaA were detected and sequenced in 37 (74.0%) out of the 50 cave environmental samples and in 10 (55.6%) out of the 18 samples of water catchment sediments. Nine species of slowly growing mycobacteria (M. terrae, M. arupense, M. gordonae, M. lentiflavum, M. parascrofulaceum, M. parmense, M. saskatchewanense, M. simiae and M. xenopi) and two subsp. (M. avium subsp. avium and M. avium subsp. hominissuis) were detected. Fourteen species of rapidly growing mycobacteria (M. chelonae, M. chubuense, M. poriferae, M. flavescens, M. fortuitum, M. porcinum, M. rhodesiae, M. gilvum, M. goodii, M. peregrinum, M. mageritense, M. vanbaalenii, M. gadium and M. insubricum) were detected. The highest mycobacterial presence was documented by ZN staining and/or culture examinations in earthworm castings and bat guano (73.3% positivity out of the 15 samples) in the cave environment and in the water sediments collected under the outflow from the wastewater treatment plants (77.8% positivity out of nine samples). The highest total organic carbon (TOC) was detected in wooden material and earthworm castings with pH values between 5.0 and 7.7 in the cave environment and in water sediments collected under the outflow from the wastewater treatment plants with pH between 5.8 and 7.0. It could be concluded that the karst cave environment with its running surface water contaminated with different microorganisms or chemical substances creates favourable conditions not only for animals (especially earthworms) but also for mycobacteria. This fact is also demonstrated by the presence of these mycobacteria in the cave environment mainly in earthworm castings and bat guano.