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Effects of culture densities on feed demand, behavioural tests and on the hepatic and cerebral oxidative status in tilapia (Oreochromis sp.)

Abstract:

The present study examines whether fish density affects behavioural tests, feed demand, and different parameters indicative of the oxidative status of the liver and brain of Orechromis sp. to identify welfare indicators for fish culturing. The fish were maintained at two commercial densities (5.6 and 16.2 kg/m3) and hand fed for 4 weeks (four replies/treatment). At the third week, two replies at each density were provided for self-feeders. At the fourth week, fish were subjected to behaviour tests and sampled for oxidative status studies. To examine the effect of chronic stress caused by the density of farming and animal response to acute stress on oxidative stress, six fish/treatment was sampled before behaviour testing and six fish/treatment after behaviour testing. To study behavioural tests 10 fish/treatment were submitted three behaviour tests: an open-field test followed by a neophobia test and an object presentation repeat test. The oxidative stress was determined by quantifying free malondialdehiyde (FrMDA), protein-bound malondialdehyde (PrMDA), protein hydroperoxides (PrOH), hydroperoxides (LOOH) and thiobarbituric acid reactive substances (TBARs). In addition, the total antioxidant capacity (TEAC) and expression and activity ofglucose-6-phosphate dehydrogenase were determined. No differences among treatments for oxidative status were found. Under acute handling stress, both lots, LD/HF and HD/HF, in both tissues increased the parameters indicative of oxidative damage in brain (p < 0.05). The feeding behaviour shows a diurnal activity in low-density, while high-density didńt demand feed. The results suggested that farmed tilapia culture at a density of 16 kg/m3shows slightly altered fish behaviour, and only significant differences were observed open field test in low density fish, between self-feeder and hand feeding groups. The object presentation repeat, showing higher exploration movement in high-density fish regarding low density and hand −feeding fish. Furthermore, the fish at high density did not use demand-feeders and showed a decrease in the expression and activity of G6PDH. These two markers can be used to assess the welfare status of tilapia and to study the welfare status in other farmed fish.