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This study aimed to assess the effect of constant darkness applied to fish during controlled breeding on reproductive traits in domesticated females of Eurasian perch. Based on the assumption that keeping fish in constant darkness during the reproduction operation may reduce stress, suspected to be responsible for variable spawning effectiveness in this species. Two conditions were assessed (16 h light per day [group 16L] and constant darkness [group 0L], two tank replicates per condition). The reproductive protocol involved a 7-day-long adaptation period for group 0L where photoperiod was reduced by 2.3 h a day down to constant darkness. After the adaptation period, two hormone injections (salmon gonadoliberin analogue) were applied to both groups: priming (10 µg/kg) and resolving (25 µg/kg) with a 7-day interval between them. During the study, morphometric indices were recorded and blood, brain, and pituitary samples were collected to assess stress markers and determine hypothalamic-pituitary-gonadal axis functioning via measuring blood plasma hormones, as well as gonadoliberin and gonadotropins (luteinising hormone [LH] and follicle-stimulating hormone [FSH]) transcript abundance (n = 7 for each group at each sampling point). In addition, kinetics of the final oocyte maturation (FOM) process, ovulation rate, and egg quality of each group was monitored (n = 12 for each group). The results indicated that there were no differences in terms of morphometry, FOM kinetics, and most stress indices between groups throughout the experiment, except haematocrit, which increased immediately following the acclimation period in fish kept in darkness. Constant darkness negatively affected plasma levels of 17α,20ß-dihydroxy-4-pregnen-3-one (DHP) and LH transcript expression at the time of the second hormone injection. This indicated that exposure to constant darkness negatively affected priming of the hormonal dose applied, resulted in the disruption of ovulation, and reduced ovulation rates (50%) for group 0L, as compared to 16L (91%). The findings of this study clearly indicate that constant darkness may have significant deleterious effects on reproductive traits throughout out-of-season induced, hormonally supported, controlled reproduction. Therefore, we advise against the use of constant darkness when managing broodstock reproduction in domesticated Eurasian perch.

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The aim of this study was to compare physiological responses in Siberian sturgeon (Acipenser baeri) induced by propofol and CO2 anaesthesia. Two procedures were applied during the experiment. In procedure I, blood samples were collected immediately after exposure (1, 2, 5, 10 min) to the anaesthetic. In procedure II, fish were exposed to the anaesthetic for 10 minutes and then were moved to anaesthetic free water. Blood was sampled after 5, 10, 20 or 30 min of recovery time. Gasometrical and biochemical analyses were performed on collected blood. In CO2 anaesthetized fish strong hypercapnic acidosis was revealed. The drop of the HCO3-/CO2 ratio, from 28:1 in control fish up to 4:1 in CO2 anaesthetized ones, proved that the compensation mechanism is not capable of preventing acidosis during CO2 anaesthesia in Siberian sturgeon. In contrast, only moderate, respiratory acidosis occurred in sturgeons anaesthetised with propofol. Hypercapnic acidosis during CO2 anaesthesia was followed by a fourfold increase of ammonia level in the blood. Glucose level, increasing only during recovery time, indicates that a secondary stress response occurred when awareness of anaesthetized fish had been restored.

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Propofol, 2,6-diisopropylphenol, seems to be a good candidate as a fish anaesthetic, however, no study regarding propofol influence on fish has yet been reported. The aim of this study was to examine propofol pharmacokinetics in rainbow trout (Oncorhynchus mykiss) following bath exposure. Fish (n = 100) were exposed to an aqueous propofol bath at 12°C and 17°C; propofol concentration in the bath was 10 mg L(-1). Plasma concentration-time profiles were determined using LC-MS, and pharmacokinetic parameters were calculated. Propofol was absorbed quickly at both temperatures. Its concentration reached 13.8 ± 2.7 µg mL(-1) and 16.1 ± 2.1 µg mL(-1) at 12°C and 17°C, respectively, during the first minute of exposure. Blood plasma propofol decreased rapidly to 6.8 ± 0.7 µg mL(-1) and 6.3 ± 2.2 µg mL(-1) at 12°C and 17°C respectively, during the first 10 minutes of the recovery. The half-life time of propofol was 1.5 h and 1.1 h at 12°C and 17°C, respectively. We found propofol anaesthesia in trout effective and safe. However, it caused a gradual decrease of respiratory rate, and therefore a specific anaesthesia protocol should be developed.

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Laboratory-bred goldfish were experimentally infected with Contracaecum rudolphii, either directly (with nematode larvae) or indirectly via infected zooplankton. Intensity and prevalence of infection were markedly higher in fish exposed to the infected zooplankton than in goldfish exposed to nematode larvae. When transmitted to fish via the zooplankton, larvae developed much faster and, after 8 weeks, became firmly encysted in the intestine wall. The digestive tract of larvae isolated from the intestine wall showed a well-developed ventriculus, ventricular appendix and intestinal caecum. The mouth was surrounded by three lips. When free-living larvae induced infection, they rapidly penetrated the intestine wall and migrated to internal organs (e.g. liver). The primordial lips of those larvae were poorly visible, the ventricular appendix was short, and the intestinal caecum was absent. During the 10-week experiment, no encysted larvae were found in fish infected with free-living larvae.

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The premise that free amino acid or dipeptide based diets will resolve the nutritional inadequacy of formulated feeds for larval and juvenile fish and improve utilization of nitrogen in comparison to protein-based diets was tested in stomachless fish, common carp (Cyprinus carpio L.) larvae. We examined the postprandial whole body free amino acid (FAA) pool in fish that were offered a FAA mixture based diet for the duration of 2 or 4 weeks. We found that the total amount and all indispensable amino acids concentrations in the whole body decreased after a meal. We then fed juvenile carp with dietary amino acids provided in the FAA, dipeptide (PP), or protein (live feed organisms; brine shrimp Artemia salina nauplii, AS) forms. Histidine concentrations in the whole fish body increased in all dietary groups after feeding whereas all other indispensable amino acids decreased in FAA and PP groups in comparison to the AS group. Taurine appears to be the major osmotic pressure balancing free amino acid in larval freshwater fish which may indicate a conditional requirement. We present the first evidence in larval fish that in response to synthetic FAA and PP diets, the whole body indispensable free AA concentrations decreased after feeding. This study shows that amino acids given entirely as FAA or PP cannot sustain stomachless larval fish growth, and may result in depletion of body indispensable AA and most of dispensable AA. The understanding of these responses will determine necessary changes in diet formulations that prevent accelerated excretion of amino acids without protein synthesis.

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