Ontogeny of the digestive enzyme activity of the pikeperch (Sander lucioperca) under culture condition.

The pikeperch (Sander lucioperca) is a species with a high potential for aquaculture and a valuable food with high market acceptance. The aim of the study was to evaluate the functional ontogeny of digestive enzyme of pikeperch from hatching to 45 days-post fertilization, 777 degree-day (DPF, dd) under culture condition. The average total length (TL) of larvae measured at hatching was 3.6 ± 0.4 mm (5 DPF; 67 dd) and at the end of experiment (45 DPF, 777 dd) was 27.1 ± 1.1 mm. The survival rate was 80-90% during the experiment period. Inhibition zimography reveals the presence of nine bands with proteolytic activity in the digestive tract of juvenile pikeperch. Zimography results during the ontogeny revealed that in larvae at 8 DPF (108 dd) and 13 DPF (189 dd), three bands were presented. The variations observed in the enzymatic activity reflected a high amount of total protease activity at 10 DPF (133.5 dd). Regarding pepsin, its activity was observed for the first time at 26 DPF (378.9 dd). Lipase activity remained constant from hatching to 26 DPF (378.9 dd). The highest amount of α-amylase activity was detected at 15 DPF (211.5 dd) and 45 DPF (777 dd). The low lipase enzyme activity suggested that live feeds with low lipid were more suitable than diets containing high lipid levels; larvae had also early capability to digest nutrient-dense diet that was high in protein. According to results the pikeperch larvae possess after the exogenous feeding, a functional digestive system with high activities that indicated the gradual development of the digestive system.

The effectiveness of human chorionic gonadotropin in stimulation of second spermiation in pikeperch Sander lucioperca during the spawning season.

The aim of the present study was to evaluate the effectiveness of human chorionic gonadotropin (hCG) in stimulation of second spermiation in already reproduced pikeperch males during the same spawning season. Fish (mean weight 919.9 ±â€¯236.9 g) were divided into the control saline-injected group, and two groups injected with 200 and 400 IU hCG/kg body weight. Forty-eight hours following injection (at a temperature of 16.7 °C) the percentage of fish producing useable amounts of semen increased from 30% in the control group up to 80% in the treated fish and the highest volume of semen was recorded in fish treated with 400 IU/kg BW hCG. Spermatocrit (50.7 ±â€¯9.1%) and sperm concentration (17.5 ±â€¯5.0 × 109 spermatozoa/mL) were significantly higher in control fish than those recorded in hCG-treated fish (24.8 ±â€¯7.7% and 8.1 ±â€¯2.4 × 109 spermatozoa/mL in 200 IU/kg; 32.3 ±â€¯17.6% and 10.9 ±â€¯7.5 × 109 spermatozoa/mL in 400 IU/kg). No significant differences were observed between the groups with respect to sperm motility (as a spermatozoa activity time and percentage); however, a change in plasma alkaline phosphatase activity was found in the group injected with 400 IU/kg of hCG. The lack of significant differences in plasma metabolites and cortisol between control and hCG-treated fish indicated that the hCG had no effect on the stress response. Testosterone levels were significantly increased in the hCG-treated fish, whereas no significant differences in 17ß-estradiol were recorded. No differences between the groups in plasma levels of thyroid hormones suggested lack of hCG-induced effect on hypothalamus-pituitary-thyroid axis. The results of this study demonstrated that the spermiation of already reproduced pikeperch males could be induced by hCG during the same spawning season. Based on the results on semen volume and concentration, injection with hCG could improve the efficiency of pikeperch reproduction to reduce the number of brooders and costs of juvenile pikeperch production.

Short-term effects of 17ß-estradiol on physiological responses in stellate sturgeon Acipenser stellatus.

There is no evidence of the effect of 17ß-estradiol (E2) administration on stress response and related metabolites after a short-period in chondrostean. In this study, we examined whether E2 is capable of inducing the hypothalamus-pituitary-interrenal axis activity. To accomplish this, sexually immature Acipenser stellatus were injected intraperitoneally with saline or E2 (5mg/kg body mass) and sampled 0, 1, 3, 6, 12, 24, 48, and 72h later. Plasma E2, cortisol, glucose, lactate, hematocrit (Hct), total protein (TP), cholesterol, triglyceride, alkaline phosphatase activity (ALP), calcium (Ca), and phosphorus concentrations were examined. Plasma levels of E2 significantly increased after 1h in E2-injected fish and remained high after 12h. E2 injection enhanced plasma TP and Ca concentrations, but had no effect on other parameters. Injection of either saline or E2 enhanced plasma glucose, lactate, TP, and Ca concentrations, but had no effect on Hct, cholesterol, triglyceride, and ALP. The results demonstrated that acutely elevated level of E2 did not lead to intense changes of stress metabolites and altered biochemical changes compared to the fish in control or saline treatment groups. Therefore, we found no exhibition of E2 on the rate of cortisol synthesis or stress indicators in this species, while E2 could modulate some other related metabolites on vitellogenesis pathway.

Long-term effects of intraperitoneal injection of estradiol-17ß on the growth and physiology of juvenile stellate sturgeon Acipenser stellatus.

Juvenile stellate sturgeon Acipenser stellatus were intraperitoneally injected with estradiol-17ß (E2; 0 and 5 mg/kg fish) to investigate the possibility of sex reversal and also determine the changes in biochemical parameters. Five-month-old fish (40.9 ± 1.1 g) were injected every 3-week interval during a 190-day trial. At the termination of the experiment, final weight and other growth parameters including weight gain and specific growth rate, hepatosomatic and viscerosomatic indices were not affected by repetitive injection of E2. Hematological features of E2-treated fish showed significant reductions in number of red blood cells, hemoglobin concentration, hematocrit value and mean corpuscular hemoglobin (P < 0.05), but no significant changes were observed in number of white blood cells, mean corpuscular volume and mean corpuscular hemoglobin concentration (P > 0.05). Calcium, phosphorus, glucose, triacylglycerol, cholesterol, total protein and estradiol concentrations were significantly increased in fish injected with E2 (P < 0.001). Plasma progesterone and testosterone levels were noticeably lower in fish injected with 5 mg/kg E2 rather than the control fish (P < 0.001). Histological observations of gonads showed that all fish injected with 5 mg/kg E2 apparently feminized, while 66.6 % of the control group was female. These results revealed that the injection of E2 is an effective method for feminization of stellate sturgeon without having significant inhibitory effects on growth and survival.

Physiological changes in male and female pikeperch Sander lucioperca (Linnaeus, 1758) subjected to different photoperiods and handling stress during the reproductive season.

Pikeperch broodstocks were exposed to different photoperiods: constant light (24L:0D), constant darkness (0L:24D), and 12 h light, 12 h darkness (12L:12D), for 40 days. Half of the broodstocks of each photoperiod were exposed to handling stress at a specific time of the day. Results showed that cortisol and lactate did not reveal any significant difference. However, glucose levels in females increased in the stress-free darkness period in comparison with stressful darkness photoperiods (0L:24D-s). Red blood cells in males and white blood cells in females showed a significant difference under different photoperiod regimes. Both sexes showed no significant difference in the differential count of leukocytes under different photoperiods and handling stress. Constant photoperiods and handling stress affected the hematological parameters, particularly, the number of lymphocytes and neutrophils in females. Our findings revealed that due to a long-term exposure to stressors, pikeperch brooders become adapted to stressful conditions.

Effects of different photoperiods and handling stress on spawning and reproductive performance of pikeperch Sander lucioperca.

The objective of this study was to control the reproductive cycle of pikeperch (Sander lucioperca) through determining the effects of different photoperiods and handling stress on the reproduction quality, timing and quality of spawning, fertilization, sex steroids, and cortisol concentrations. In this study, 72 pikeperch broodstocks with an average weight of 1367 ± 55.3 g were exposed to different photoperiods including constant light (24L:0D), constant darkness (0L:24D), and 12 h of light, 12 h of darkness (12L:12D) for 40 days. Half of the broodstocks of each photoperiod treatment were exposed to handling stress at a specific time of the day. Applying different photoperiods caused changes in the timing of broodstocks' spawning, so that fish under 24L:0D spawned earlier than those of other photoperiods, and stressed fish of the 0L:24D photoperiod had a delayed spawning compared to others. Also, the spawning of the broodstocks at different photoperiods which were exposed to handling stress was either delayed or did not occur at all. The highest and lowest spawnings were observed in the morning and at night, respectively. Fertilization percentage, number of eggs per gram, sex steroids including estradiol, progesterone, and testosterone, as well as cortisol and calcium concentrations did not show any significant difference in different photoperiods and handling stress. In stressed males of the 24L:0D photoperiod, there only was a significant decrease of testosterone concentration compared to the beginning of the experiment. Results indicated that the spawning performance of pikeperch broodstocks could be considerably stimulated using an effective photoperiod. Similarly, pikeperch broodstocks in culture systems are usually affected by handling stress, and this stress could lead to a poor reproductive performance and inhibition of spawning.