Jan Mareš

Accumulation of Microcystins in Nile Tilapia, Oreochromis niloticus L., and Effects of a Complex Cyanobacterial Bloom on the Dietetic Quality of Muscles

The aim of this study was to investigate the kinetics of accumulation and elimination of microcystins in the tissues of Nile tilapia (Oreochromis niloticus) and to evaluate the effect of cyanobacterial exposure on fish muscle quality (levels of total fat and ash, protein, dry matter and the composition of saturated, monounsaturated and polyunsaturated fatty acids). Fish were exposed for 28xa0days to a natural cyanobacterial bloom with total microcystin concentration around 1,200xa0μgxa0g−1 biomass dry weight. The hepatopancreas accumulated microcystins up to 350xa0ngxa0g−1 fresh weight, but concentrations in muscle were generally below the detection limit (2xa0ngxa0g−1 fresh weight). Following the exposure, fish were moved to the clean water, but only minor microcystin removal from the hepatopancreas was observed during a 4xa0week depuration period. Exposures of tilapia to the complex cyanobacterial bloom had only minor and temporary impacts on the investigated parameters of dietetic quality.

Concentrations of microcystins in tissues of several fish species from freshwater reservoirs and ponds

The aim of this study is to summarise the determination of concentrations of microcystins (MCs) in muscle and liver of freshwater fish species caught in stagnant waters of the Czech Republic. Within the years 2007–2009, 351 muscle samples and 291 liver samples of 16 freshwater fish species derived from four fishponds, and four water reservoirs were analysed. MCs were detected in 53 liver samples. The highest concentrations of microcystins were determined in liver samples of carnivorous fish species; 50.3xa0ng/g of fresh weight (FW) in perch (Perca fluviatilis) and 22.7xa0ng/g FW in pikeperch (Sander lucioperca). MCs in liver were detected in other five fish species; asp (Aspius aspius), pike (Esox lucius), common carp (Cyprinus carpio), grass carp (Ctenopharyngodon idella) and European eel (Anguilla anguilla). Concentrations of MCs in liver of nine fish species (European bream, whitefish, tench, silver carp, European catfish, roach, chub, crucian carp and rudd) were below the detection limit of 1.2–5.4xa0ng/g FW for different MC congeners. However, the concentrations of MCs in all muscle samples were below the detection limit. The assessment of MCs concentrations might be influenced by the detection method used. Due to the concentrations of MCs being below the detection limit in muscle samples of all fish species analysed, it seems that there might be a low potential threat for human health in case of fish muscle consumption.

Prediction of mercury bioavailability to common carp (Cyprinus carpio L.) using the diffusive gradient in thin film technique

The mercury bioaccumulation by common carp (Cyprinus carpio L.) tissues (gills, skin, eyes, scales, muscle, brain, kidneys, liver, and spleen) and the capability of the diffusive gradient in thin film (DGT) technique to predict bioavailability of mercury for individual carps tissues were evaluated. Carp and DGT units were exposed to increasing concentrations of mercury (Hg2+: 0xa0μgxa0L-1, 0.5xa0μgxa0L-1, 1.5xa0μgxa0L-1 and 3.0xa0μgxa0L-1) in fish tanks for 14 days. In the uncontaminated fish group, the highest mercury concentration was determined in the muscle tissues and, in fish groups exposed to mercury, the highest mercury concentration was determined in the detoxification (kidneys) and input (gills) organs. A strong and positive correlation between the rate of mercury uptake by the DGT technique and the rate of mercury accumulation by fish tissues (gills, skin, scales, and eyes) was observed.

In vivo effects of microcystins and complex cyanobacterial biomass on rats (Rattus norvegicus var. alba): Changes in immunological and haematological parameters

Toxic cyanobacteria represent a serious health and ecological problem in drinking and recreational waters worldwide. Some previous toxicological studies investigated effects of isolated microcystins on laboratory rodents including mice and rats. However, much less attention has been paid to more realistic exposure situations such as the effects of MCs accumulated in food. The objectives of the present study were to provide a simple model simulation of the food chain in order to evaluate impacts of microcystins (MCs) on rat immune and haematologicalparameters. Impacts of feeding experimental rats with a diet containing fish meat with and without microcystins and complex toxic biomass have been studied during a 28 day exposure. Red blood cell parameters (RBC counts, haematocrit values, MCH, MCV and MCHC) showed significant differences in experimental groups (pxa0≤xa00.05, pxa0≤xa00.01) in comparison with the control group. We also detected an immunomodulatory effect in the experimental groups. NK cells and γδ+ T lymphocytes were significantly increased in peripheral blood in the group exposed to isolated microcystin in the food. Significant change in the ratio of CD4+ and CD8+ cells (increase of CD4+ and a drop in CD8+) was found in the group with added cyanobacterial biomass with low concentration of MCs. The greatest changes in lymphoid organs were observed in the same groups. There was an increase of spleen subpopulations of γδ+ T lymphocytes as well as of IgM+ lymphocytes (B lymphocytes) and CD8+ T lymphocytes. Indeed, the modulation of CD4+ and CD8+ of peripheral lymphocytes was associated with similar changes in thymic lymphocytic subpopulations. In summary, food containing fish meat with considerable doses of microcystins (or toxic cyanobacterial biomass) induces significant changes in RBC parameters and influence preferably innate part of the immune system represented by NK cells and by gamma-delta T cells, which are known to play role as a bridge between adaptive and innate immune response.

Impact of microcystin containing diets on physiological performance of Nile tilapia (Oreochromis niloticus) concerning detoxification.

Nile tilapia (Oreochromis niloticus) were fed by diets supplemented with cyanobacteria containing in part the cyanotoxin microcystin-LR (MC-LR) to determine the potential impacts on detoxification. Four different diets were prepared based on a commercial diet: (1) control, (2) MC-5% (containing 5% dried Microcystis sp. biomass with 4.92 μg MC-LR g(-1) diet), (3) MC-20% (containing 20% dried Microcystis sp. biomass with 19.54 μg MC-LR g(-1) diet), and (4) Arthr-20% (containing 20% dried Arthrospira sp. biomass without MC-LR). Blood and liver samples were taken after one, 7, and 28 days and protein has been determined in plasma and liver. In the liver, impacts on detoxification were measured by glutathione-S-transferase (GST) activities and gene expression of multi drug resistance protein (MDRP). Plasma protein did not change between all four diets at any sampling time whereas liver protein was significantly elevated already after one day in Arthr-20% and after 28 days in both, MC-20% and Arthr-20%. Biochemical measurements of GST activities revealed no significant impact at any sampling time. In order to characterize the potential effect of MC-LR on MDRP, RT-qPCR method was established. However, as for GST activities no significant changes in MDRP gene expression have been observed. Thus, in summary, oral exposure of MC-LR containing cyanobacteria to Nile tilapia via feed ingestion did not impact significantly detoxification in liver concerning GST activities and MDRP expression despite biochemical composition concerning liver protein was significantly elevated by the diets containing 20% cyanobacteria biomass, regardless whether they contained MC-LR or not.

Haematological indices are modulated in juvenile carp, Cyprinus carpio L., exposed to microcystins produced by cyanobacterial water bloom

This study evaluated the influence of toxic cyanobacterial water blooms on the blood indices of the common carp, Cyprinus carpio L. Experimental fish were exposed to a natural population of cyanobacterial water blooms (mainly Microcystis aeruginosa and M. ichthyoblabe), which contained microcystins [total concentration 133-284 μg g⁻¹ (DW), concentration in water 2.8-7.4 μg L⁻¹]. Haematological indices showed marked changes in fish exposed to the cyanobacterial population in comparison with the control group. Statistical evaluation of the influence of cyanobacterial water blooms on biochemical indices of the juvenile carp showed a distinct decrease in albumin, alanine aminotransferase, total bilirubin, calcium, cholesterol, glucose, phosphorus and iron when compared to controls. Values of red blood counts [haemoglobin, haematocrit (PCV), mean corpuscular haemoglobin and mean corpuscular haemoglobin concentration] and lactate were significantly increased compared to controls. After exposure to cyanobacterial water bloom, the carp were kept in clean water to monitor the persistence of biochemical indices. The influence of cyanobacterial populations on calcium, cholesterol, glucose, lactate, phosphorus and PCV persisted up to 28 days after conclusion of the experiment. Duration of exposure, toxicity and density of cyanobacterial water blooms had an important impact on individual haematological indices.

The food of roach, Rutilus rutilus (Actinopterygii: Cypriniformes: Cyprinidae), in a biomanipulated water supply reservoir

Roach, Rutilus rutilus (Linnaeus, 1758); bream, Abramis brama (Linnaeus, 1758); and European perch, Perca fluviatilis Linnaeus, 1758 typically dominate fish stocks in water supply reservoirs (drinking water reservoir) of the Czech Republic (Pivnicka 1992). Roach are feeding generalists, usually utilising the most available food resource (Hellawell 1972, Prejs and Jackowska 1978, Prejs 1984, Horppila and Nurminen 2009). Such dietary plasticity allows it to find food in habitats offering less than ideal conditions for other species, whose feeding demands may be greater (Barus and Oliva 1995). Planktonic crustacean such as Cladocera and Copepoda tend to dominate in the food of younger age classes; Tarvainen et al. (2002), for example, found 0+ roach (71–90 mm) to be exclusively zooplanktivorous (Bosmina, Chydorus), while Hammer (1985) observed the same cladoceran species dominating roach fry diet in Lake Lankau (Germany). Similarly, Vasek et al. (2006) as well as Peterka and Matěna (2009) have both described ACTA ICHTHYOLOGICA ET PISCATORIA (2014) 44 (1): 15–22 DOI: 10.3750/AIP2014.44.1.03

Proliferative kidney disease in rainbow trout ( Oncorhynchus mykiss ) under intensive breeding conditions: Pathogenesis and haematological and immune parameters

Proliferative kidney disease (PKD) is an endoparasitic disease of salmonid fish caused by Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea). This study presents a comprehensive view on PKD development in rainbow trout (Oncorhynchus mykiss) reared at an intensive fish breeding facility, with focus on mortality, pathology/histopathology, haematological findings and immune functions. Diseased and reference fish were sampled monthly and time course of natural infection was followed up from the onset of clinical signs (September 2014) to full recovery (January 2015). PKD- associated cumulative mortality was 30% with a peak value in October, while immunohistochemical testing indicated a continuous significant decrease in T. bryosalmonae numbers from September to December; with no parasites detected in January. During peak clinical infection, a significant decrease in red blood cell counts, haematocrit values, haemoglobin concentration, along with a reduction in lymphocytes and a significant phagocyte elevation corresponding with an increase in phagocyte oxidative burst were measured in comparison to control animals. Complement activity and total immunoglobulin plasma concentrations were also elevated, though only during the initial monitoring period (September). Individuals surviving PKD, recovered and were able to fully regenerate both renal structure and haematopoietic parameters to normal levels. Changes in the red blood cell parameters indicate anaemia and a decreased oxygen transportation capacity during the clinical disease phase. Together with an increased oxygen demand at higher temperatures and decreased oxygen solubility this could lead to decompensation and elevated mortality. The stimulation of immune parameters, and especially oxidative phagocytic burst, is likely to have had a strong effect on both, regeneration and elimination of the pathogenic agent.

Seasonal changes in immune parameters of rainbow trout (Oncorhynchus mykiss), brook trout (Salvelinus fontinalis) and brook trout × Arctic charr hybrids (Salvelinus fontinalis × Salvelinus alpinus alpinus).

Despite the high number of studies concerning seasonality of immune response in fish, information for some fish species is still scarce. Here, we assess seasonal changes in leukocyte counts and several immune parameters in three groups of farmed salmonids, i.e. brook trout (Salvelinus fontinalis), brook trout x Arctic charr hybrids (Salvelinus fontinalis x Salvelinus alpinus alpinus) and rainbow trout (Oncorhynchus mykiss) reared under the same conditions and fed with the same feed. Fish were sampled in five periods of the year (late April, early July, late August, early November and early February) and leukocyte counts, respiratory burst of blood phagocytes, lysozyme concentration in skin mucus and total complement activity were measured. Generalized linear models using fish body length as a continuous predictor and sampling period and fish species as categorical predictors, were significant for each of the parameters analysed. The highest seasonal variations in measured parameters were found in rainbow trout and lowest in hybrids. Our results confirm that measures of innate and adaptive immunity are strongly affected by season in all three groups of salmonids. The results will contribute to the improved assessment of immunocompetence in farmed fishes, essential for future sustainable development in aquaculture.

The influence of physicochemical properties of water on plasma indices in brook trout (Salvelinus fontinalis, Mitchill) reared under conditions of intensive aquaculture

The breeding of salmonids in intensive aquaculture has increasing importance in terms of high quality fish crude. The aim of our study was to figure out if the physicochemical properties of water can influence the physiological condition of fish organism. Blood samples were taken from the heart of 86 healthy, randomly selected brook trout (Salvelinus fontinalis) with the standard length of 242.3 ± 10.8 mm and body mass of 261.10 ± 29.81 g. Sampling was done on three trout farms in the Czech Republic in the period between autumn 2009 and summer 2011. Blood plasma was analysed for the presence of 23 plasma indices by automated blood plasma analyser. Chemical properties of water had a significant (P < 0.001) influence on the content of alkaline phosphatase, cholinesterase, amylase, lipase, total protein, albumin, P, Ca and K in plasma of the brook trout. Plasma indices were influenced especially by water temperature, oxygen saturation, and the content of ammonium ions, total nitrogen, iron and conductivity. This is the first complex study focusing on the influence of chemical and physical composition of water on blood plasma indices of brook trout. Fish, salmonids, biochemical variables, chemical properties, fish farming Development of intensive aquaculture requires the examination of the state of health of fish including also approaches that involve clinical biochemical diagnostics. Such approaches serve to identify the onset of any organ failure caused by the use of wrong feeds and to draw attention to changes in the abiotic factors of the environment and to any complications due to infection or parasitic invasion. To identify as many pathological deviations as possible, it is advisable to use more than one test reflecting the basic metabolic functions (Řehulka and Minařik 2008). Fish blood plasma chemistry is a promising area in fish biology and clinical pathology although it requires further research particularly in assessment of normal range. More studies need to be performed with a focus on the clinical analysis of blood as an indicator of the physiological state of the brook trout in aquaculture (Diouf et al. 2000; Řehulka and Minařik 2007). Moreover, apart from the inevitable differences in, e.g. methodology, fish size and strains, season and physiological condition, it is often difficult to find an exhaustive set of blood chemistry which estimates for trout in a single study (Manera and Britti 2006). The aim of the present study was to assess plasma indices in brook trout (Salvelinus fontinalis) from aquaculture system. The basic characteristics of fish organism physiological condition through selected biochemical indices of the blood plasma were examined.