The effect of artificial feed on blood biochemistry profile and liver histology of wild saddled bream, Oblada melanura (Sparidae)

Floating fish farms attract a great number of wild fish species, changing their behaviour and physiology. The saddled bream, Oblada melanura, sampled from populations aggregated around the Adriatic fish farm and from natural/control populations, were analysed for differences in eleven blood biochemistry parameters and liver histomorphology. The levels of lactate dehydrogenase (LDH), alkaline phosphatase (ALKP) and urea (URE) in cage-associated saddled bream (428.00 ± SD 321.56 U/L, 86.13 ± SD 39.87 U/L and 0.05 ± SD 0.16 mmol/L, respectively) were significantly lower than those observed in the control specimens (1047.06 ± SD 505.56 U/L, 125.75 ± SD 34.70 U/L and 1.99 ± SD 0.73 mmol/L, respectively). In contrast to that, concentrations of aspartate aminotransferase (AST) in cage-associated fish (87.63 ± SD 132.34 U/L) were higher than values noted for the control population (6.55 ± SD 5.90 U/L). URE and AST presented the main variables contributing to the discrimination between two analysed populations. One-way ANOSIM based on the blood parameters showed significant difference between saddled bream that fed around cages and those from the remote waters (R = 0.697; P < 0.01). Hepatocytes of cage-associated fish contained large cytoplasmatic clear spaces indicating excessive accumulation of fat in the hepatocyte cytoplasm. All observed differences can be attributed to contrasting feeding behaviour of sampled populations but basic nutritional differences between them should be quantified in the future. Moreover, further research is necessary to detect their impact on the health status of the fish.

Research highlights
► Oblada melanura around the cages used food pellets as the food resource.
► Change of the feeding pattern affected its blood indices (some values differed. significantly between two studied populations) and liver histomorphology.
► Morphological pattern in liver, known as steatosis, occurred in cage-associated fish.