Scale matters: performance of European sea bass,Dicentrarchus labrax, L. (1758), reared in cages of different volumes

Abstract

The effects of rearing volume on on-growing European sea bass performance and stress parameters were investigated for the first time in a pilot aquaculture farm. Fish were held under the same initial stocking densities in triplicate net-pen cages of different sizes (1.4, 45 and 252 m 3 ) for a period of 8 months. Results showed significant differences among the experimental groups in most parameters tested, with better performance in the two larger rearing volumes. In particular, growth rate showed a linear association with rearing volume, being 0.68 g day À1 for the large cage group, 0.56 g day À1 and 0.32 g day À1 for the medium and the small groups respectively. The feed conversion ratio and per cent survival (%) were also better in the large cage group. Fish reared in the small and medium-sized cages showed higher plasma cortisol concentrations than those reared in large cages, which showed low basal cortisol concentrations. Additionally, after an acute chasing stress challenge, fish in the large and small groups, but not the medium group, showed increased cortisol concentrations. Differences also occurred in the ratio of the expression of cortisol receptors, namely the mineralocorticoid (mr) and glucocorticoid receptors (gr). In specific, the ratio of mr to gr mRNA expression in the liver was higher in fish reared in the small cages. These findings verify that experimental scale significantly affects experimental results and is a critical factor for the interpretation of results.

Allostatic Load and Stress Physiology in European Seabass (Dicentrarchus labrax L.) and Gilthead Seabream (Sparus aurata L.)

“…It is shown here that seabass subjected to increasing intensity of (chronic) stress mildly elevate basal plasma cortisol levels (range: 50–200 ng/ml; Figure 2 ) compared to controls; remarkably, basal levels of cortisol in seabass are remarkably high compared to the generally accepted “non-stress” level seen in most fish (up to 20 ng/ml). Seabass is in general characterized by high cortisol values and variation ( 27 , 28 , 39 , 58 , 59 ), and the current results point out that chronic stress can further increase these high (basal) cortisol levels.…”

Repeatability of cortisol stress response in the European sea bass (Dicentrarchus labrax) and transcription differences between individuals with divergent responses

“…unbound) cortisol were measured by the use of a commercial enzyme immunoassay kit (DRG ® Cortisol ELISA, DRG ® International Inc, Germany). The performance of the kit has been previously evaluated with linearity and recovery tests in E. sea bass plasma samples 28 .…”

“…This species shows an intense stress response 25 and is considered susceptible to stress by inducing reproductive dysfunctions and disease outbreaks 26 , which, in turn, hamper production. Moreover, cortisol concentrations are characterized by high variability in both basal and response levels, so between studies 27 as between individuals of the same population 28 . Consequently, it is of great importance to gain better knowledge on the stress physiology of this species by investigating the divergence of the response among individuals, since stress responsiveness can affect their performance 9 21 .…”

Regulation of divergent cortisol responsiveness in European sea bass, Dicentrarchus labrax L.

“…Plasma cortisol and cortisol released in the superfusion medium by the head kidney were measured using a commercial enzyme-linked immunoassay kit (DRG ® Cortisol ELISA, DRG ® International Inc, Germany), previously evaluated in this species [ 29 ]. Plasma ACTH concentrations were assayed by a commercial, specialized for fish, enzyme-linked immunoassay kit (CUSABIO ® Fish Adrenocorticotropic hormone ELISA kit, CUSABIO BIOTECH Co. Ltd, China).…”