Effects of Background Color on Growth, Stress, Biochemical, Hematological, and Immunological Responses, and Expression of Growth-Related Genes in Oscar Fish (Astronotus ocellatus)

The aim of the current study was to assess the impacts of tank color on the growth, stress, biochemical, hematological, and immunological responses, and expression of growth-related genes in juvenile Oscar (Astronotus ocellatus). Therefore, a total of 120 fish (9.14 ± 0.34 g) were distributed into 12 aquariums (60 × 50 × 35 cm) and divided into four treatments (aquariums with blue, white, yellow, and red colors) in three replicates (10 fish per aquarium). The fish were daily hand-fed ad libitum in three meals at 7:00, 12:00, and 17:00 hr for 56 days. Results showed that Oscar fish cultured in the red aquariums had higher final weight and weight gain and lower feed conversion ratio. Plasma cortisol, glucose, and lactate values of fish were significantly higher, and the amount of white blood cells was lower in the blue aquariums compared to other tank colors. Plasma triglyceride values were significantly higher in the white and yellow groups than the blue aquariums. Moreover, fish cultured in yellow and red aquariums had significantly higher melatonin levels than the blue aquariums. Plasma cholesterol, total protein, albumin, complement 3, and total immunoglobulin values were highest in Oscar fish cultured in the red aquariums. Also, lysozyme and alternative complement (ACH50) activities and complement 4 values of fish cultured in yellow and red aquariums were meaningfully higher compared to blue and white groups. Growth hormone relative gene expression levels were meaningfully higher in Oscar fish cultured in white, yellow, and red aquariums than the blue aquariums. Furthermore, insulin-like growth factor-1 (IGF-1) relative gene expression levels were significantly higher in fish cultured in yellow and red aquariums compared to those cultured in blue and white tank colors. Thus, the most suitable tank color for rearing juvenile A. ocellatus is red, while blue tank color is unsuitable.