Jean-Louis Gaignon

Selection method of new candidates for finfish aquaculture: the case of the French Atlantic, the Channel and the North Sea coasts

At present, European marine fish farming is based on sea bream and sea bass. A trend for diversification is sustained by the diversity of environmental conditions, by the availability of new production techniques such as recirculating systems, by an increase in rearing yields, by new market trends and by the possibilities to reduce risks of disease outbreak. Already reared fish species were chosen considering a limited number of criteria such as a high selling price and the availability of juveniles or breeders in the wild. This paper proposes a new selection method of fish species as candidates for aquaculture development on the French Atlantic, the Channel and the North Sea coasts. Using a three-phase procedure, candidates were selected among 20 000 fish species. Final classification was carried out using a panel of 22 criteria, taking into account inquiries conducted in France with aquaculturists but also with the main actors of distribution and transformation channels and with consumers. Cod (Gadus morhua) was selected by the present work as the first candidate for aquaculture development on the western coasts of France. This work also highlights the high interest of Gadoids for aquaculture development in this area.

Thermal induction of gynogenesis and triploidy in Atlantic salmon (Salmo salar) and their potential interest for aquaculture

Abstract Triploid and gynogenetic progenies were produced in Atlantic salmon with moderate thermal shocks (26–29°C) applied soon after fertilization. Yields of gynogenetics were high (60–70% of control at start feeding); gynogenetics proved to be all female and could be helpful in the establishment of populations of sex-reversed females to produce all-female livestock in that species. All-triploid groups were also obtained with a wide range of thermal treatments and good survival (66–89% of control at start feeding). Nevertheless, at the age of 2.5 years, triploids displayed lower survival and growth in weight than their control, which may limit their practical interest for aquaculture.

Gill (Na+K+)-ATPase activity and smolting in Atlantic salmon (Salmo salar L.) in France

Abstract A survey of the gill (Na + K + )-ATPase activity in yearling Atlantic salmon reared in a hatchery in Brittany was conducted during 3 years. In 1982, in a French strain, the gill enzymatic activity increase occurred in the second half of March, after the equinox. The growth rate was variable in the population and two clear length modes appeared during the fall and winter, the larger fish presenting obvious smolt characteristics. There is a clear relationship between the limiting size found only from the intensity of the level of the gill enzyme activity and the size separating the two length modes. The large fish mode corresponds to the smolts. In 1983, in a Norwegian strain, ATPase activity began to increase earlier, and in 1984, in the same strain, increased even earlier, well before the equinox. Temperature, rather mild in Brittany in winter, remained at the same value and cannot be involved in the enzyme activation. Growth rates and absolute size are probably able to modify the receptivity of the fish to environmental parameters, and subsequently to modify the date of smoltification.

Effects of rearing conditions on growth and thyroid hormones during smolting of Atlantic salmon, Salmo salar L.

Smolting Atlantic salmon, Salmo salar L., grew faster in large (22.5 m2) than in small tanks (4 m2). Their tri-iodothyronine (T3) levels were higher in small than in large tanks on 26 March and 2 April; and their thyroxine (T4) levels were higher in small than in large tanks from 26 March to 11 April, but surged simultaneously in all tanks. T4 appears related to fish length until the beginning of April, but not after the surge. The fish grew faster at low water velocity and flow (9 cm/s, and 20 l/min) than at high (40 cm/s, and 90 l/min). Their T3 levels were consistently lower at high flows; and their T4 levels surged simultaneously under low, but earlier at high flows.

Effect of some repetitive factors on turbot stress response

The stress response of the turbot, Scopthalmus maximus (L.), to repetitive factors including netting, air exposure, blood sampling and hand-stripping, were tested using two different tank sizes as well as two blood sampling techniques. Exposure of juvenile fish to air for 1-4 min had no immediate effect on plasma cortisol concentrations or haematocrit values. Similarly, the serial netting of immature fish from tanks did not significantly modify plasma cortisol concentrations, haematocrit or osmolarity values. Hand-stripping of mature males was more disturbing than air exposure. The cumulative effect on plasma cortisol levels and osmolarity of stress factors such as netting, air exposure, blood sampling and stripping applied simultaneously to mature males in a 16 m3 tank and repeated twice daily for several days was recorded. The level of cortisol increased from 5 ng ml-1 to 300 ng ml-1 after 10 days of treatment, while an osmoregulatory imbalance and fish death were observed. Moreover, adaptation of fish to smaller tanks seemed to improve the increased plasma cortisol levels and death rate. Reduction in the number of stress factors applied greatly decreased both the range of physiological responses and the death rate. In order to avoid a cumulative stress response, handling of fish should therefore be reduced to a minimum.

CHANGES IN THE DYNAMICS OF STRUCTURED WATER AND METABOLITE CONTENTS IN EARLY DEVELOPING STAGES OF EGGS OF TURBOT (PSETTA MAXIMA)

Abstract The dynamics of structured water and the contents in main metabolites were determined using two techniques of nuclear magnetic resonance (NMR) for the developing eggs of the flatfish Psetta maxima . The unfrozen water (structured water), and its thermodynamic properties were modified during embryogenesis, especially in two developmental stages, from ova to morula (8 h), and from organogenesis (70 h) to the pre-hatching stage (128 h). These modifications were closely related to the metabolization of vitelloproteins and consequently to the concentration of aminoacid and choline compounds.