G. Koumoundouros

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.

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.

Growth and Body Composition of Zebrafish (Danio rerio) Larvae Fed a Compound Feed from First Feeding Onward: Toward Implications on Nutrient Requirements

Although zebrafish is used as a major model species for understanding a number of biological functions and mechanisms involved, there is practically no information on the nutritional requirements of this cyprinid. The rearing practices, especially with regard to feeds and feeding, also vary considerably. To obtain base line information on the nutrient requirements and to develop a standard diet, we initiated the present work of feeding zebrafish larvae with a formulated feed right from first feeding onward. Growth of zebrafish fed the compound feed was very good, reaching a total length of 23 ± 4 mm in 9 weeks with a survival rate of 89% ± 4%. We present the first ever published data on whole-body composition in terms of essential amino acids (ideal protein profile), total, neutral and polar fatty acid profiles, minerals, and trace elements. Results obtained here show clearly that zebrafish can be reared with formulated feed right from mouth opening without resorting to any live prey.

Imbalanced dietary ascorbic acid alters molecular pathways involved in skeletogenesis of developing European sea bass (Dicentrarchus labrax).

The influence of dietary ascorbic acid (AA) on growth and morphogenesis during the larval development of European sea bass (Dicentrarchus labrax) was evaluated until 45days post hatching. Diets incorporated 0, 5, 15, 30, 50 or 400mg AA per kg diet to give AA-0, AA-5, AA-15, AA-30, AA-50 and AA-400 dietary treatments, respectively. Dietary AA levels lower than 15mg/kg reduced larval growth and survival was affected in specimens fed diets devoid of AA. Globally, disruption of the expression of genes involved in AA and calcium absorption in the intestine (SVCT-1, TRPV-6), skeletogenesis (BMP-4, IGF-1, RARγ) and bone mineralization (VDRβ, osteocalcin) were observed in groups fed doses lower and higher than 50mg AA/kg diet. Such disturbances detected at molecular level were associated with disruptions of the ossification process and the appearance of skeletal abnormalities.