Histomorphometric evaluation of melanomacrophage centers (MMCs) and CD3+ T cells of two morphs of brown trout (Salmo trutta) fed diets with immunostimulants.

The brown trout (Salmo trutta) is a salmonid residing in riverine and coastal waters throughout the Northern Hemisphere, whose various populations evolved into distinct ecological morphs, differing in their migratory tendencies and preferred habitats. Unfortunately, due to progressing degradation of natural environment, the conservation of these populations is of growing importance and is undoubtedly a challenging task. Therefore, various means to refine the preparatory protocols for restocking using hatchery-reared fish are being pursued, some of which involve the administration of immunity-boosting substances. The current study assessed the effects of two dietary immunostimulants: Bioimmuno (4% inosine pranobex and 96% ß-glucan) and Focus Plus (commercial preparation by Biomar, Denmark) on two morphs of the brown trout - the river trout (S. trutta morpha fario) and the sea trout (S. trutta morpha trutta). Tissue samples were obtained from ∼75 to 100g fish after 0, 2 and 4 weeks of experimental feeding. Multi-factorial analysis of conducted histological measurements of melanomacrophage centers (MMCs) revealed no changes of their parameters within spleens, but showed a decrease of the occupied tissue area and MMC counts in the livers, progressing with time regardless of the applied diet. Immunohistochemical analysis of CD3+ T cells showed their increased recruitment into mucosal folds of pyloric caeca in the 2-week sampling of trouts fed with the diet with 2% Bioimmuno addition, but this effect was not present in the 4-week sampling. When studying all groups jointly within each morph, there was a significant difference in terms of maintained CD3+ T cells levels, as sea trouts showed significantly higher tissue areas occupied by these cells than river trouts, both in the pyloric caeca and hepatic parenchyma. The study revealed that feeding with a diet enriched with Bioimmuno for 2 weeks may be a favorable enhancement of rearing protocols of brown trout stocks prior to their release, but more studies need to be conducted to test the possibility of an even shorter feeding period.

Muscle Tissue Quality of Raw and Sous-Vide Cooked Wild and Farmed Pikeperch.

The aim of the study was to compare the chemical and fatty acid composition, colour, and sensory quality of wild and farmed pikeperch. Raw wild pikeperch had a higher moisture and ash contents, as well as pH value, but lower fat and protein contents than farmed pikeperch. In sous-vide fillets, a higher fat and a lower protein content were noted in farmed fish. Slight differences in colour attributes between farmed and wild fish affected neither chroma nor hue in raw and sous-vide fillets. Wild and farmed fish fillets prepared using sous-vide were scored similarly in the sensory assessment. Although wild fish had a more beneficial fatty acid composition demonstrated by a higher proportion of polyunsaturated fatty acids, including eicosapentaenoic and docosahexaenoic, a higher fat concentration in farmed pikeperch resulted in obtaining similar or even higher concentration of these fatty acids in sous-vide fillets. Regardless of the origin of pikeperch it might be recommended as a valuable part of a daily diet.

Effect of Different Routes of Vaccination against Aeromonas salmonicida on Rearing Indicators and Survival after an Experimental Challenge of Pikeperch (Sander lucioperca) in Controlled Rearing.

Bacterial diseases are a significant problem in the controlled rearing of fish. Furunculosis (Aeromonas sp.), flavobacteriosis (Flavobacterium sp.), and pseudomonadosis (Pseudomonas sp.) are currently the most frequently identified diseases in recirculating aquaculture systems of various fish species. Such a situation is also observed in pikeperch rearing. Due to the emerging difficulties of effective prophylaxis using commercial vaccines, interest in the use of autovaccinations is increasing, not only in ichthyopathology but also in other veterinary fields. Our research aimed to assess the effect of the vaccination method on the overall condition of the fish and survival after the experimental infection with Aeromonas salmonicida. Pikeperch were vaccinated by (1) bath, (2) a single i.p. injection, or (3) feed. The fish were measured and weighed on day 0 and after 28 and 56 days of the experiment. Specific growth rate, daily growth rate, condition factor, and feed conversion ratio were calculated. On days 7, 14, 21, and 28 of the experiment, ceruloplasmin and lysozyme levels were rated. In addition, a challenge test was performed. The obtained results showed that the method of vaccination is important and affects the growth of fish, the overall condition of fish, and survival after experimental infection.

Impact of inducing general anesthesia with Propiscin (etomidate) on the physiology and health of European perch (Perca fluviatilis L.).

The aim of the study was to describe the course and timing of the different stages of anesthesia induced with Propiscin (etomidate) on juvenile European perch (experiment I) and to describe the effect of immersing specimens of this species had on selected hematological and biochemical parameters (experiment II). The study was conducted on material with body weights (BW) of 162.98 (experiment I) and 171.60 g (experiment II). In experiment I, general anesthesia was induced with two different anesthetic concentrations (1 or 2 ml l-1; anesthesia time 10 min). In experiment II, blood was drawn for hematological and biochemical analyses from the fish that had been exposed to anesthetic immersion baths with two different concentrations of Propiscin (1 and 2 ml l-1) and for different exposure times (3 and 10 min). Blood samples were collected immediately following immersion (0 h) and 24 h later (24 h). Specimens that were immersed at the higher concentration of anesthetic achieved subsequent stages of general anesthesia two times faster (P ≤ 0.05). However, during recovery, some statistically significant differences were observed, but these lasted only until stage I was achieved. Among the hematological parameters (0 h), significant differences were observed in hematocrit (HCT) and mean corpuscular volume (MCV), while among the biochemical determinations (0 h), statistically significant differences were noted in the concentrations of glucose, calcium, lactate, and ammonia. After 24 h, the levels of these parameters in all fish groups returned to initial values. The hematological and biochemical tests conducted permit concluding that the anesthetic tested, at the concentrations (1 and 2 ml l-1) and the exposure times of up to 10 min at which it was tested, is safe and can be used successfully to induce general anesthesia in perch.

The effects of surgically implanted dummy tags on the survival, growth performance, and physiology of pikeperch (Sander lucioperca).

The aim of this work was to determine the impact of surgically implanted telemetry transmitters (TTs) on the growth, survival, hematological and biochemical indexes, and wound healing in juvenile pikeperch (Sander lucioperca) (body weight 60-90 g). Two incision suturing methods were used-silk sutures (experiment I-group ST) or tissue adhesive (experiment II-group GT). After tagging, the fish were held in a recirculating system for 35 days. No statistically significant differences were noted in the growth or condition indexes analyzed among the fish tagged with TT compared with those from the control groups (untagged). Substantial individual variability was noted, however, in the parameters examined in both the control and tagged groups. Among the hematological indexes, statistically significant differences were only noted in experiment I. Lower values of mean corpuscular volume and mean corpuscular hemoglobin were noted in group ST. Among the biochemical parameters, creatinine was statistically significantly threefold lower, magnesium and alkaline phosphatase (ALP) levels were lower, and ammonia levels were higher in group ST than in the control group. In experiment II, significant differences were only noted for ALP. Tissue adhesive was the superior and more effective method for closing the incision after TT implantation in juvenile pikeperch. This type of suturing facilitated faster healing, and it had less of an impact on juvenile pikeperch welfare.

Propiscin--A safe anaesthetic for pikeperch (Sander Lucioperca L.).

The aim of this work was to determine the impact of etomidate (Propiscin) dose (1 and 2 ml l-1) and exposure time (2 and 10 min) on the biochemical and haematological parameters of juvenile pikeperch (Sander lucioperca) [mean body length (Lc) 25.9 cm; body weight (W) 189.9 g] that were reared in a recirculating aquaculture system (RAS). Significant changes in the mean values of total protein, globulin, calcium, magnesium, and ammonia were noted in all groups immediately following exposure. The greatest changes in the haematological indicators were observed in groups subjected to 10-min exposure at both doses of the anaesthetic. The specimens from these groups had higher values for white blood cells (WBC), red blood cells (RBC), haemoglobin (HGB), haematocrit (HCT), and mean corpuscular volume (MCV). Statistically significant differences in these same parameters were also noted in the groups of fish exposed to the anaesthetic for 2 min at a dose of 2 ml l-1, but they were not as pronounced. Twenty-four h following exposure to etomidate, all blood parameters in the experimental groups were comparable to those of the control group. Etomidate can be recommended as a safe, effective anaesthetic for pikeperch.

Impact of butyl benzyl phthalate on development of the reproductive system of European pikeperch, Sander lucioperca (L.).

The effect of butyl benzyl phthalate (BBP) on the sex differentiation process of fish is practically unknown. The experimental material of this study was juvenile European pikeperch [Sander lucioperca (L.)], which is gonochoristic, undergoes immediate sex differentiation, and has a fixed gonad differentiation period. The fish were fed a diet supplemented with BBP (during the sex differentiation phase: age 61-96 days post hatch) in the following quantities: 1.0; 2.0; 4.0; 8.0; 16.0 g BBP kg-1 feed. The control feed was a xenobiotic-free base feed. In the present experiment lasting 10 weeks, the survival and growth of fish, the histopathological changes of the fish gonads and the sex ratio were evaluated. After administration of the two highest doses of BBP, growth inhibition of the fish was observed. BBP also seriously disturbed the gonadal differentiation process of pikeperch. All analysed concentrations of BBP delayed testicular development and, at concentrations of 4.0, 8.0 and 16.0 g BBP kg-1, induction of the feminisation process was observed. The sex ratio was distinctly disrupted in groups receiving 8.0 and 16.0 g BBP kg-1.

Impact of diets with different proportions of linseed and sunflower oils on the growth, liver histology, immunological and chemical blood parameters, and proximate composition of pikeperch Sander lucioperca (L.).

The aim of the study was to determine the impact of applying different proportions of linseed (LO) and sunflower (SFO) oils in pikeperch diets on growth, histological changes in the liver, immunological and blood chemical parameters. The fish were fed isoenergetic and isoprotein feeds containing SFO (group 100SFO) or LO (group 100LO) in quantities of 67 g kg/feed, and a mixture of oils: 47 g SFO and 20 g LO kg/feed (group 70SFO/30LO) and 20 g SFO and 47 g LO kg/feed (group 30SFO/70LO). Dietary ratios of polyunsaturated fatty acids from the n-3 and n-6 series (n3/n6 index) were 0.36-2.15. Pikeperch were reared for 56 days in three replicates for each dietary treatment. Various dietary oils and ratios of n3/n6 did not impact fish growth, feed conversion ratio, viscerosomatic and hepatosomatic index, and size of the hepatocytes. Feeding the fish high quantities of LO and SO oils (groups 100LO and 100SFO) reduced the immunological response of the phagocytes and lymphocytes in the fish. Moreover, this resulted in significant differences among groups in the quantity of linolenic and linoleic acid in whole fish bodies, viscera, fillets, and livers. Various quantities of vegetable oils in the fish diets did not impact the quantity of arachidonic, eicosapentaenoic and docosahexaenoic acid in the fillets and livers. The immunological index and low quantities of linoleic acid in the fillets obtained in group 30SFO/70LO indicate that the n3/n6 dietary ratio of 1.35 was the most advantageous for feeding juvenile pikeperch feeds with vegetable oils.

Influence of heavy metals and 4-nonylphenol on reproductive function in fish.

Many industrial and agricultural chemicals (including heavy metals and alkylphenols) present in the environment have adverse effects on the reproductive function in fish. Three studies were conducted to assess toxicity of these chemicals towards reproduction of freshwater fish. It was shown that heavy metals added to the diets accumulate in brain tissue of carp, and this accumulation results in inhibition of the secretion of noradrenaline and stimulation of the secretion of dopamine in the hypothalamus. These processes results in a disturbance of hormonal equilibrium of the hypothalamo-pituitary system, which can unfavorably influence the efficiency of artificial spawning in fish. Quality of salmonid and sturgeon sperm was impaired after in vitro exposure to heavy metals. The degree of this toxic effect was species-specific. It was demonstrated that sperm motility parameters appeared to be good indicators of adverse effects of heavy metals fish sperm. The protection role of seminal plasma against toxic effects of heavy metals was suggested for salmonid fish. Oral application of 4-nonylphenol (NP) disrupted reproduction in pikeperch. In juvenile fish a decrease in the percentage of males and an increase of intersex fish was observed in relation to dose of NP and time of exposure to this alkylphenol. Exposure of adult males to the NP led to the reduction in fecundity, milt quality and fertility.