A study was carried out to investigate the effects of background colour on the growth performance, skin colour, haematology, physiological condition and non‐specific immune responses of goldfish, Carassius auratus. Goldfish were reared in tanks with four different background colours (white, black, blue and red) for 8 weeks. Fish growth performance markedly rose in white background compared with the other treatments. There was no significant difference in haematological parameters or plasma proteins concentrations between treatments. Plasma cortisol of fish reared in red background was significantly higher than that in black and white backgrounds. Plasma antiprotease and lysozyme activities were more than doubled in white and black treatments compared with the red and blue groups. The other immune parameters tested (plasma peroxidase, complement and bactericidal activities) did not significantly change between treatments. Skin carotenoid content and the intensity of fish skin colour extremely diminished in white background. This study revealed that red and blue backgrounds are chronically stressful and immunosuppressive in goldfish. White backgrounds will preferably be used for the culture of goldfish for best fish growth. However, a way to revert the colour loss of goldfish skin reared in white backgrounds remains to be investigated.

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Early-life exposure to mild stressors can assist animals in coping with more stressful events in later life. This study was aimed at investigating how early stress and dietary lipid contents affect growth, hematology, blood biochemistry, immunological responses, antioxidant system, liver enzymes, and stress responses of oscar (Astronotus ocellatus) ( 6.8 ± 0.7  g). Six experimental treatments were HL0Stress (high-lipid diet and without stress), HL2Stresses (high-lipid diet and two-week stress), HL4Stresses (high-lipid diet and four-week stress), LL0Stress (low-lipid diet and without stress), LL2Stresses (low-lipid diet and two-week stress), and LL4Stresses (low-lipid diet and four-week stress). During the ten-week trial, fish fed high-lipid diets grew faster ( 46.41 ± 4.67 vs. 38.81 ± 2.81 ) and had a lower feed conversion ratio (2.21 vs. 2.60) than those fed low-lipid diets ( P < 0.05 ). After acute confinement stress (AC stress), high-lipid groups had higher survival than low-lipid treatments (81.25% vs 72.92%) ( P < 0.05 ). Fish subjected to two-time stress (2Stresses) had a higher survival rate after AC stress (90.63% vs. 62.50%), hematocrit, white blood cell, blood performance, total protein, high-density lipoproteins, cholesterol, triglyceride, alternative complement activity (ACH50), superoxide dismutase, glutathione peroxidase, and alkaline phosphatase levels than those not stressed ( P < 0.05 ). Contrariwise, glucose, cortisol, alanine aminotransferase, and aspartate aminotransferase levels were significantly lower in the 2Stresses groups compared with 0Stress fish ( P < 0.05 ). Collectively, these findings suggest stressing the signs of adaptation in 2Stresses fish. However, a higher number of early stress events (4Stresses) appears to exceed the threshold of manageable stress levels for this species. In conclusion, the HL2Stresses group outperformed the other treatments in terms of growth, health status, and stress responsiveness. Although fish welfare must be considered, these results suggest that early mild stress can result in a greater survival rate after fish are exposed to later acute stress.

In this study, the effect of short-term starvation (0, 1 and 2 weeks) on biochemical parameters and nonspecific immune response of tinfoil barb (Barbonymus schwanenfeldii) was investigated. Fish in three different groups were deprived of feed for 0 (control), 1 (S 1 ) and 2 (S 2 ) weeks, respectively. At the end of the experiment, blood samples were collected for biochemical and immunological analyses. The results indicated that plasma glucose, cholesterol and peroxidase levels and haemolytic complement activity were significantly lower in starved fish for 2 weeks than those in fed fish and in starved fish for 1 week. Plasma lysozyme activity significantly changed in different starvation periods in all treatment groups. However, no significant effect was observed on plasma antiprotease activity. There were significant differences between the control and the food-deprived groups in plasma triglyceride levels. Starvation increased plasma total protein, albumin and globulin in the deprived groups compared with the control group. The results of this study showed significant changes in nonspecific immune parameters, plasma glucose levels and other metabolites in this species after feed deprivation that are indicative of the relationship between starvation effects and the extension of starvation period. ARTICLE HISTORY

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Plasma chemistry, lipid metabolism and vitellogenin gene expression of captive Sterlet sturgeon Acipenser ruthenus were studied in different maturity stages. A total of 32 fish were sampled, and maturity stages were identified on the basis of histological criteria and direct observation. Females were classified to four groups: previtellogenic, vitellogenic, post-vitellogenic, and atresia. Blood, gonad and liver tissue samples were taken through non-lethal biopsy. Our results showed that plasma levels of glucose, cholesterol, triacylglycerol, high-density lipoprotein, low-density lipoprotein, very low-density lipoprotein, calcium, phosphorus, alkaline phosphatase activity, albumin and total protein increased during ovarian development and were highest at post-vitellogenic stage. The lowest amounts in atresia stage demonstrate that lipid and energy imbalance was related to reabsorption and digestion of the yolk. These results suggested that the VLDL was the main plasma lipoprotein component of Sterlet. We determined that lipoprotein lipase and hepatic lipase activity increased during vitellogenesis process which suggested the role of lipase enzymes in regulating blood lipid metabolism. RT-PCR analysis indicates that Vitellogenin (VTG) mRNA could be detected both in livers and ovaries of female Sterlet. Throughout the study, the expression level of VTG gene showed an increase both in ovaries and in livers reaching its peak at late vitellogenesis stage. This strongly indicated a relation between VTG mRNA and ovarian development.

Summary The objective of this study was to evaluate the feeding rate of the great sturgeon (Huso huso) young of the year (YOY) and to investigate the effects of different feeding rates in maintaining the weight of fish during short periods of winter starvation. Six feeding rates of 0.2, 0.4, 0.6, 0.8, 1.0% body weight (BW) day−1 and feeding to satiation were considered for the first experiment. Each feeding rate was randomly assigned to three replicate tanks, with continuous feeding throughout a 5‐week winter period of water temperatures below 10°C. Fifteen fish were held in each of 18 tanks with an average initial body weight of 219.6 ± 6.9 g. After 5 weeks of feeding, the best performance was observed in fish fed 1% BW day−1, but negative growth was observed in fish fed 0.2% BW day−1. In the second experiment, fish were deprived of feed for 3 weeks at winter temperatures. Weights and condition factors of all fish decreased during starvation, while the differences in mean weight before and after the starvation period were not significant in fish fed a level of 0.2% BW day−1 and those fish fed to satiation. No mortality was recorded in either experiment. Results of this study indicate that a feeding rate of 1% BW day−1 would be sufficient for commercial fish farming of YOY of this species to maintain them over winter. Also, to maintain fish weights and prevent weight loss in overwintering ponds, a feeding rate of around 0.3% BW day−1 seems appropriate for hatcheries.

The dynamics of stress responses in small, juvenile pikeperch Sander lucioperca (as a representative teleostean) and small, juvenile Persian sturgeon Acipenser persicus (as a chondrostean) were determined during capture and transportation for release into rivers. Blood samples were obtained from juveniles from a pond, channel, and loading basin and at 1.5 and 24 h after loading. Samples were analyzed for cortisol, glucose, and lactate concentrations, and mortality was recorded. Plasma cortisol concentrations increased, reaching a maximum in Persian sturgeon from the channel and pikeperch from the loading basin. Significant increases in plasma glucose concentrations were observed in samples from the channel and at 1.5 h after loading for Persian sturgeon and pikeperch, respectively. Similarly, significant decreases in lactate concentrations were observed 1.5 h after loading in both species. The results of this study show the sensitivity of these species to stress during transportation. They suggest a higher resistance to transportation stress by the sturgeon than the pikeperch, but it is highly recommended that transportation procedures and capture techniques be modified so that they are appropriate for the species.