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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