Maroudio Kentouri

Normal and abnormal osteological development of caudal fin in Sparus aurata L. fry

Normal osteological development of the caudal fin in gilthead sea bream is described at the larval and juvenile stages. It was used as a standard for the study of a sea bream larval population with characteristic osteological deviations which give rise to abnormal juveniles. Normal specimens were reared under extensive rearing conditions, and abnormal specimens under intensive rearing conditions. The first hypural elements appearing in the abnormal preflexion larvae were deformed and displaced. With development, all elements related to the caudal region (parhypural, hypuralia, epuralia, vertebra centra, neural and haemal processes) formed abnormally. The abnormalities were extra-numerous elements, fusions, deformities and displacements of the elements.

Effect of water currents on the development of skeletal deformities in sea bass (Dicentrarchus labrax L.) with functional swimbladder during postlarval and nursery phase

Abstract Lordosis in reared sea bass was previously related either to the absence of swimbladder, or to bad or late inflation of this organ when damages were irreversible. Our results prove that these explanations are insufficient and that similar deformations may occur frequently in fry with functional swimbladder during the early weaning phase, if currents in tanks are higher than 10 cm s −1 .

The effect of rearing conditions on development of saddleback syndrome and caudal fin deformities in Dentex dentex (L.)

Abstract The development of saddleback syndrome and of caudal fin deformities in Dentex dentex (Linnaeus, 1758) was compared under two rearing methods, extensive (E) and semi-extensive (S). The osteological appearance and the meristic characters of the reared fish were compared to that of D. dentex juveniles, collected from the natural environment. All the wild juveniles were normal in respect to their osteological appearance, while the reared specimens presented skeletal deformities resulting from different rearing methods applied. Saddleback syndrome (4.0–4.4%) and severe external deformities of the caudal fin (14.3–15.0%) characterised exclusively the semi-extensive populations, while the extensive populations presented severe abnormalities of the pre-ural centra (25.0–25.6%) with significantly higher frequency than the S reared fish (5.8%). Saddleback syndrome was expressed as a lack of one to all the hard spines of the dorsal fin, accompanied by shape, number and position abnormalities of the related pterygiophores. Caudal fin deformities were mainly characterised by the lack of the upper lepidotrichia or/and dermatotrichia, accompanied by severe deformities of the supporting elements of the upper lobe. The saddleback syndrome and severe caudal fin deformities were anatomically and ontogenetically related to each other, originating at the early larval stage as a result of abnormalities of the primordial marginal finfold and of the posterior tip of the notochord. In respect to the dominant phenotypes, the meristic characters of the normal reared fish were not differentiated from those of the wild, but they presented higher variability. The results are discussed in view of the aetiology, applications and research targets for the erasure of skeletal malformations.

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.

The opercular complex deformity in intensive gilthead sea bream (Sparus aurata L.) larviculture. Moment of apparition and description

Abstract External morphology, head morphometry and osteology were used for early detection, description and heuristic study of the opercular complex abnormalities of intensively reared gilthead sea bream larvae (Sparus aurata). The first evidence of malformations were observed in larvae of 6.1 mm total length (TL). The abnormalities were fully developed during metamorphosis (11.0–22.0 mm TL), i.e., before the end of the hatchery phase. In 81.4% of the abnormal fish, the problem was unilateral with similar right/left frequency. In 85.5% of the cases, it was associated with severe foldings and twists of the operculum and/or suboperculum and rarely with an atrophy of these bones. The etiology, aquaculture applications and research targets for the erasure of skeletal malformations are discussed.

Diel feeding activity and the effect of time-restricted self-feeding on growth and feed conversion in European sea bass

The feeding rhythm and growth performance of European sea bass Dicentrarchus kzbrar (initial weight 65 g) were studied under free and time-restricted access to self-feeders. Under free access to the feeders, significant feeding rhythms with a nocturnal acrophase were observed, although there was considerable variability between replicates. When access to the self-feeders was restricted to two periods of 4 h day-‘, the feed demand (FD) was reduced at the beginning of the experiment but not at the end, indicating that the period of adaptation, rather than appetite, was affected by such feeding practice. When access to the self-feeders was restricted to only one period of 4 h day- I, two thirds of the replicates eventually displayed FD similar to the fish having free access to feed, indicating that the restricted temporal access to feed could be compensated for. There was no detectable effect of feeding protocol on feed conversion or body composition, but growth was closely related to the total FD. Thus, growth was influenced by the fact that fish subjected to a time-restricted access to feed needed time to adapt to the new feeding situation. The results indicate that sea bass are capable of operating self-feeders, and can easily modify their feeding, resulting in both good growth performance and good feed conversion. Kqvwords: Sea bass; Self-feeding; Growth; Feed conversion

Kyphosis in reared sea bass (Dicentrarchus labrax L.): ontogeny and effects on mortality

The ontogeny and the effects of vertebral kyphosis on the mortality rate of reared sea bass (Dicentrarchus labrax) are described. The first evidence of deformities was observed in individuals of 10 mm total length (TL) in the form of light malformations or bilateral asymmetries of individual vertebrae. At 14 mm mean TL, the 18.2% of the reared fish presented severe vertebral kyphosis at the pre-haemal region. Kyphosis continued to develop and presented its maximum incidence at 17 mm TL (24.8%). The centre of the deformity was mainly located on vertebrae 5–6. Kyphotic specimens presented a lethargic behaviour. After 17 mm mean TL, the incidence of the deformity decreased exponentially over time due to the heavy mortality of the affected fish (24.8% kyphosis incidence in the surviving fish vs. 52.6% in the dead fish collected from the tank, p<0.01). For the first time, it was shown that although a skeletal deformity could have little effect on the final quality of the reared juveniles, it can significantly affect the mortality rate and thus the productivity of the hatcheries. The results are discussed with respect to the aetiology, applications and research targets for the erasure of skeletal malformations from the reared fish.

Effect of heavy metals on fish larvae deformities: A review

Heavy metals have been associated with many fish deformities in natural populations and in laboratory produced specimens as well. Deformities in general have devastating effects on fish populations since they affect the survival, the growth rates, the welfare and their external image. Although the embryonic stage in respect to heavy metal exposure has been extensively studied, there is not much information available as to what happens in fish larvae and adults. In the present article, we present the available information on the effect of heavy metals on fish larvae deformities. We also address the need for more research towards the effects of metals on the subsequent life stages in order to assess the long-term consequences of heavy metal poisoning on fish organisms and possibly correlate these consequences with the environmental contamination (use as biomarkers).

Mesocosm: a reliable technology for larval rearing of Diplodus puntazzo and Diplodus sargus sargus

Species diversification is today considered as a major issue for the sustainable development of the Mediterranean aquaculture. For successful propagation of any species however, larval rearing is considered a bottleneck and therefore the development of appropriate tools is essential. Mesocosm is a semi-intensive technology that facilitates larval rearing of several species integrating principles of both intensive and extensive aquaculture, which solves biological problems and many of their technical, human and economical consequences. The extensive (and now even the semi-extensive) strategy is used in the most critical segments of the rearing process during the early developmental stages, when larvae are still extremely weak, sensitive to intensive environment, easily stressed and difficult to feed. The intensive strategy is used as soon as larvae are considered mature enough to be reared easily using classical methods. The technology was used for the rearing of two species, with potential for aquaculture, the sharpsnout seabream (Diplodus puntazzo) and the white seabream (Diplodus sargus sargus). Three groups of each species were monitored for a period of 50–70 days post hatching. Survival for both species was about 54% at the end of the trials. Sharpsnout seabream larvae reached 19.6 ± 0.9 mm total length and 107.2 ± 31.9 mg body weight 50 days post hatching. White seabream larvae 60 days post hatching reached 32.7 ± 2.7 mm total length and 450 ± 70 mg body weight. In order to verify the economical viability of the technology, the individual production cost for each species was estimated and reached ¢0.027 for white seabream and ¢0.043 for sharpsnout seabream. Results indicate the reliability of the technology for the larval rearing of the two species.

Methanol as alternative carbon source for quicker efficient production of the microalgae Chlorella minutissima: Role of the concentration and frequence of administration

Autotrophic cultures of the marine microalgae Chlorella minutissima were performed at 13 000 lux continuous illumination in 1 l chambers fertilised with 0.25 g l−1 F2 medium and different doses of methanol. This was administered in two ways during two parallel experimental series of 10 days: 0.05, 0.1, 0.5, 1.0 and 5.0% methanol (v/v) in one unique dose at the beginning of the culture and 1/10 of these (i.e. 0.005, 0.01, 0.05, 0.1 and 0.5% methanol (v/v)) in daily doses for the 10-day culture period. Low concentrations of methanol induced a faster increase of cell density and dry weight than control, while high concentrations induced symptoms of toxicity. The higher cell densities and quicker growth were observed in the experiments with daily administration of 0.005 and 0.1% (v/v) methanol, while those with one dose presented an initial boosted growth but a final cell density lower than control. The role of methanol as alternative carbon source for microalgae, as well as its possible impact on the quality of biomass production and on the environment, are discussed.