Effect of rearing density on the blood and tissues of mullet (Mugil cephalus L.)

This study evaluated the biological effects of high stocking density on mullet (Mugil cephalus). Fifty fish, caught from Faro lake, were divided into two groups, a low-density control group (n = 15), stocked at 3.4 kg/m³ in an 800 l tank and a high-density experimental group (n = 35), stocked at 8.4 kg/m³ an 800 l tank. The ammonia concentration in the control group tank reached 0.3 mg/l after 2 days while that in the experimental tank reached 5 mg/l. Haematological parameters and serum protein profiles were determined following blood sampling. An Unpaired T-test showed significant differences between the two groups on Red Blood Cell Count, Haematocrit, Haemoglobin, White Blood Cell Count, Mean Corpuscular Haemoglobin, Mean Corpuscular Haemoglobin Concentration, total proteins, albumin and α-globulins. In the experimental group, the disappearance of prealbumin and the γ-globulin fraction was particularly evident. Histopathological changes indicated that mucosal electrolytic failure was the main function compromised. This could eventually lead to death. The findings suggest that mullet is sensitive to stocking density linked to ammonia toxicosis.