Chronic ulcerative dermatopathy in cultured marine fishes. Comparative study in sharpsnout sea bream, Diplodus puntazzo (Walbaum).

Chronic ulcerative dermatopathy (CUD) also known as chronic erosive dermatopathy, hole-in-the-head, head and lateral line erosion syndrome (HLLE) and lateral line depigmentation (LLD) is a chronic disease of unknown aetiology that affects the lateral line canals of the head and the trunk of various fish species. It has been described only in freshwater species although there are reports that it also affects marine fish. Here, we describe the disease in cultured sharpsnout sea bream using histology and scanning electron microscopy and identify several marine species as CUD sensitive. The results of this study correlate the development of the disease with the use of borehole water, indicating that the aetiology is probably associated with water quality rather than nutritional imbalance or infectious agents.

Thermally induced phenotypic plasticity of swimming performance in European sea bass Dicentrarchus labrax juveniles.

The vulnerability of embryonic and larval stages of European sea bass Dicentrarchus labrax to environmental temperature and the longer-term consequences for the early juveniles was demonstrated. This phenotypic plasticity was highlighted by subjecting D. labrax at 15.2 +/- 0.3 or 20.0 +/- 0.4 degrees C (mean +/-s.d.) up to metamorphosis and then at the same temperature (18.5 +/- 0.7 degrees C). After 4-6 weeks at the same temperature, the measurement of critical swimming speed at four exercise temperatures (15, 20, 25 and 28 degrees C) showed a significantly higher swimming capacity in the fish initially reared at 15 degrees C than for fish initially reared at 20 degrees C. This performance was correlated with significant differences in the phenotype of red muscle. Thermally induced phenotypic plasticity was clearly demonstrated as an important mechanism controlling swimming performance in early juveniles of D. labrax.

Evidence of temperature-dependent sex determination in the European sea bass (Dicentrarchus labrax L.).

To test the hypothesis that sex determination in the European sea bass (Dicentrarchus labrax L.) Can be affected by the incubating temperature during the very early developmental stages, eggs from the same batch of spontaneously spawned broodstock were divided at the stage of half-epiboly into three groups according to rearing temperature: G13 = 13 degrees C, G15 = 15 degrees C, and G20 = 20 degrees C. Temperature treatment lasted until the middle of metamorphosis (17-18 mm total length, [TL]), and, with the exclusion of water temperature, all biotic and abiotic conditions were identical for the three experimental groups. The on-growing phase was performed under ambient photoperiod and temperature conditions for all groups. Sex proportions were determined by histological examination of the gonads of fish at 308, 467, and 568 days posthatch (DPH). At 308 DPH (TL: 135-201 mm), 100% of the specimens had differentiated into males and females. A significantly higher (P < 0.01) proportion of females was found in groups G13 (72-74%) and G15 (67-73%) than in group G20 (24-28%). At the final sampling there was no statistically significant difference in body weight between the experimental groups. However, in all groups, female fish were larger than males (P < 0.001). Results provide for the first time clear evidence that temperature during the very early developmental stages is the crucial factor affecting the process of sex differentiation of the sea bass, with low rearing temperatures (13 or 15 degrees C) resulting in sex proportions consistently skewed in favor of females.

Seasonal variations and maturity stages in relation to differences in serum levels of gonadal steroids, vitellogenin, and thyroid hormones in the common dentex (Dentex dentex).

Seasonal variations in serum concentrations of 17beta-estradiol (E(2)), vitellogenin (Vg), testosterone (T), 11 ketotestosterone (11-KT), and thyroid hormones (T(4), l-thyroxine; and T(3), 3,5, 3'-triiodo-l-thyronine) were investigated during the first, second, and third reproductive cycles in intensively reared populations of common dentex, Dentex dentex, and correlated with gonadal development and spawning. In females, there were baseline E(2) values (<0.10 ng/ml) and negligible Vg concentrations during the postspawning and pregametogenesis period (June to December), and these increased thereafter to peak during the spawning period. Maximum T(3) and T(4) serum concentrations were found around spawning. There was a positive correlation during vitellogenesis and final maturation between Vg and T(3) (r(2) = 0.366). In addition, Vg and T(3) concentrations were statistically higher in the stages of vitellogenesis and final maturation than at the other stages (P<0.001). Minimum T(3) and T(4) concentrations (October) coincided with the decrease in water temperature and the associated decrease in the daily feeding rate and the specific growth rate. In males, as in females, seasonal changes in serum levels of T and 11-KT were well correlated with gonadal development. The presence of males in the stage of completed spermiogenesis in December coincided with the surge in both androgens and this increase lasted until the end of the spawning period. There were no significant differences in serum T(3) and T(4) levels among the maturity stages. The observed seasonal changes in serum gonadal steroids and Vg reflected the pattern of oocyte development and the spawning behavior of common dentex and were typical of the patterns described in most multiple spawners studied to date. Thyroid hormones may enhance early ovarian development and stimulate vitellogenesis in female dentex.

Unilateral eye abnormalities in reared Mediterranean gilthead sea bream.

Eye abnormalities in reared gilthead sea bream (Sparus aurata) were investigated clinically and by histological techniques. A significant number of fish had a cataract in one eye and ocular inflammation including gross exophthalmos. In a small number of fish gas bubbles were observed in the anterior chamber of the eye. Histological examination provided no evidence of an infectious process and a possible behavioural aetiology is discussed.