Fish welfare is a key factor in ensuring successful cultures. Farmed fish that are stressed have been shown to be susceptible to pathologies and present lower growth rates. The present work seeks to check the efficacy of faecal cortisol as a non-invasive method of assessing acute stress in a commercial cultured fish, the gilthead seabream (Sparus aurata). Typical stress markers (plasma cortisol, glucose and lactate) and faecal cortisol were measured in basal and post-stress (air exposure) state. Plasma and faecal cortisol, and plasma lactate after acute stress varied significantly compared to basal levels. Moreover, faecal cortisol showed a significant correlation with plasma cortisol and lactate. In conclusion, this work describes an easy, non-invasive and practical technique to assess acute stress in farmed fish. Further studies are needed to focus on other practical procedures for chronic stress measurements in sea-farms in order to improve the welfare of these animals.

The replacement of fish oil (FO) with vegetable oil (VO) in feed formulations reduces the availability of n-3 long-chain PUFA (LC-PUFA) to marine fish such as gilthead seabream. The aim of this study was to examine compositional and physiological responses to a dietary gradient of n-3 LC-PUFA. Six iso-energetic and iso-nitrogenous diets (D1–D6) were fed to seabream, with the added oil being a blend of FO and VO to achieve a dietary gradient of n-3 LC-PUFA. Fish were sampled after 4 months feeding, to determine biochemical composition, tissue fatty acid concentrations and lipid metabolic gene expression. The results indicated a disturbance to lipid metabolism, with fat in the liver increased and fat deposits in the viscera reduced. Tissue fatty acid profiles were altered towards the fatty acid compositions of the diets. There was evidence of endogenous modification of dietary PUFA in the liver which correlated with the expression of fatty acid desaturase 2 (fads2). Expression of sterol regulatory element binding protein 1 (srebp1), fads2 and fatty acid synthase increased in the liver, whereas PPARα1 pathways appeared to be supressed by dietary VO in a concentration-dependent manner. The effects in lipogenic genes appear to become measurable in D1–D3, which agrees with the weight gain data suggesting that disturbances to energy metabolism and lipogenesis may be related to performance differences. These findings suggested that suppression of β-oxidation and stimulation of srebp1-mediated lipogenesis may play a role in contributing toward steatosis in fish fed n-3 LC-PUFA deficient diets.

The bioaccessibility of total lipids and fatty acids (FA) in raw and grilled gilthead seabream (Sparus aurata) was determined using an in vitro digestion model. The particular impact of grilling on the FA profile of seabream was also studied. In addition, the influence of lipid class on the bioaccessibility of each FA was analysed. Grilling did not change the relative FA profile, and only the absolute values were altered. However, the relative FA profile varied across lipid classes, being more dissimilar between TAG and phospholipids. Long-chain SFA and PUFA seemed to be less bioaccessible. Moreover, grilling reduced bioaccessibility of protein, fat and many FA, with the highest reductions found in PUFA such as the DHA. Strong evidence supporting a predominantly regioselective action of lipase during in vitro digestion was found, and the impact of this phenomenon on FA bioaccessibility was assessed.

Age and growth of adult gilthead seabream, Sparus aurata were determined from 332 specimens (total N = 476), collected from purse-seiners, in the south-eastern Aegean Sea from November 2006 to January 2007. The fork length and body wet weight ranged from 26.5 to 51.5 cm (mean: 36.6 ± 0.18) and from 375 to 2600 g (mean: 1009.2 ± 14.16), respectively. Age groups were varied between 2 and 7. Growth parameters were estimated as L∞ = 64.97 ± 12.93 cm, K = 0.14 ± 0.07 year−1, t0 = −2.47 ± 1.09 year−1, and index of phi-prime was Φ′ = 2.772 ± 0.51. The length–weight relationship equation of all fish was calculated as W = 0.0515 × L2.737 (r2 = 0.95). The mean condition factor was estimated as 2.058. Mortalities (M, F and Z) and exploitation rate (E) of gilthead seabream from the Aegean Sea were 0.34 year−1, 0.77 year−1, 1.11 year−1and 0.69 year−1, respectively. The result of E indicated that the population was overexploited.