Elisabeth Alliot

Quantitative methionine requirement of juvenile sea-bass (Dicentrarchus labrax)

Abstract The methionine (MET) requirement of sea-bass was studied by the nutrient-response relationship using growth rate data and free MET levels in serum and whole blood after feeding. Two series of diets were employed, sharing a common basal diet. This basal diet contained a mixture of soybean, yeast and fish meals as protein source, and was formulated to be deficient in MET whereas the other essential amino acids levels corresponded to the pattern found in sea-bass muscle proteins. Graded levels of MET were obtained by supplementing the basal diet with crystalline MET (S series) or by substituting soybean and yeast meals by fish meal (F series). Fish were fed for 85 days on an optimal ration (1.5%/day). The MET requirement could be determined only with the F series diets using sigmoidal mathematical models. Inflexion points from curves obtained with the data for weight gain and for free MET in the blood were very similar. The MET requirement was estimated at about 1% of dry diet or 2% of dietary protein or 15 mg/day per 100 g live weight. The S series diets allowed us to determine, from growth data, the optimal level of MET supplementation: optimal growth rate occurred with 1.3% total MET content in the diet, with 0.6% in the crystalline form. Further supplementation depressed growth rate. Choices of types of diet, advantages of the biochemical method and use of sigmoidal models for computer fitting of experimental data are discussed.

Influence de la temperature et de la salinite sur la croissance et la composition corporelle d'alevins de Dicentrarchus labrax

Abstract Growth, food conversion, and body composition of sea bass fingerlings, Dicentrarchus labrax , exposed to different temperatures (15 and 22°C) and salinities (6, 11, 24 and 37‰) were studied. Temperature was found to have the more significant influence on these parameters. At the higher temperature, fingerlings grew faster in high and low salinities (6 and 37‰). At the lower temperature, growth was slightly faster at 11 and 24‰. Body composition was affected mainly by temperature; salinity had no significant effect. Trypsin-like activity in the digestive tract was very low at 6‰ and 15°C. Sea bass fingerlings seem to be very tolerant to changes in temperature and salinity of their environment. The results are discussed in the context of fish culture.

Responses of a Mediterranean soft bottom community to short-term (1993-1996) hydrological changes in the Rhone river.

The polychaete fauna of muddy bottoms off the Rhone delta (NW Mediterranean) was seasonally sampled at two sites at 70 m depth, from 1993 to 1996. During this period, five severe flood events occurred. A clustering analysis (distance coefficient of Whittaker) and three way fixed factor ANOVAs (site x season x year) showed strong year-to-year changes in species density and community structure, changes that masked seasonal variations. Total density increased by a factor of 3 and density of most species significantly increased following the first flooding event. Changes in the community structure were due to the successive dominance of a few species. The opportunistic species, such as Cossura sp., Mediomastus sp. and Polycirrus sp., exhibited peaks in density 1-3 months after the flood. These peaks were followed by a drastic decline. For species with a long life span, such as Sternaspis scutata, a slower but continuous increase in density was observed which was maintained for several months. The density fluctuations of these species exhibited a good correlation with river flow with time lags of 1-2 years. The successional dynamics observed are explained according to the geographical origin of the floods and the biology and feeding ecology of species.

Biogeochemical impact of a dilution plume (Rhone River) on coastal sediments: comparison between a surface water survey (1996–2000) and sediment composition

The Rhone River is the major source of nutrients and particulate matter to the Mediterranean basin. Its influence on coastal sediments was investigated by searching for the presence of continental markers. The composition of coastal sediments situated in the area influenced by the Rhone River inputs was compared with surface water salinity time-series records (five years bi-monthly survey). Sediment samples were analysed for grain-size, total and organic carbon and nitrogen, pigments, trace metals, carbohydrates, protein and lipid content. Comparisons show that changes in sediments are associated with the mean extension of the dilution plume of the river. The organic carbon content of sediments does not exhibit spatial changes related to the variations in the overlying water column. A large amount of inorganic carbon is discharged into the sea by the river and results in dilution of the organic carbon in the deposited material. The CaCO3 fraction of the total carbon of sediments is influenced by the river inputs with lower values in front of the river mouth. Changes in the composition of organic matter are linked with the inputs of the Rhone River and associated with variations of concentrations of the chlorophyll b as a marker of the terrestrial origin of the organic matter. Chlorophyll b content of sediments showed statistically significant negative correlation with the five-year bi-monthly mean surface salinity values (slope=−0.0233, R2=0.9437, n=22, p<0.001). Other parameters such as Mn content of sediments exhibit significant positive correlation with chlorophyll b and negative correlation with mean surface water salinity. Labile carbon fraction (carbohydrates, lipids and protein) shows significant correlation both with chlorophyll b and salinity. In the area influenced by the Rhone River dilution plume, there is enrichment in labile organic matter. The amounts of insoluble carbohydrates and phaeopigments suggest that this enrichment is mainly due to detritic organic matter of terrestrial origin. This twofold approach associating a long-term survey of the surface water with analysis of the sediments located beneath seems suitable for achieving a better knowledge of the environment at the sea–continent interface.

Production, respiration and ammonia excretion of two polychaete species in a north Norfolk saltmarsh

The secondary production of Nereis diversicolor and Scoloplos armiger (Annelida, Polychaeta) was studied at Stiffkey saltmarshes (north Norfolk coast). Production estimation on the basis of monthly sampling (August 1992-July 1993) gives 17.91 C m -2 y -1 for N. diversicolor, 3.37 g C m -2 y -1 for S. armiger. Oxygen consumption of individuals was studied using a respirometer at four temperatures (5, 10, 15 and 20°C). At 15 °C, the relationships between O 2 consumption (mg h -1 ) and body dry weight (mg) is Y=0.003X 0.695 for S. armiger and Y=0.003X 0.498 for N. diversicolor. Ammonia excretion of S. armiger tends to increase with decreasing temperature whereas it increases from 5 to 15°C for N. diversicolor. Carbon loss through respiration for the sampling period is estimated at 32 g C m -2 y -1 for S. armiger, and 31.7 g C m -2 y -1 for N. diversicolor. About 20% of the potential supply of phytobenthic carbon in the marsh would be converted by the populations of both species. Estimations of carbon and nitrogen budgets of S. armiger are discussed.

The Influence of water salinity on the free amino acid concentration in muscle and hepatopancreas of adult shrimps, Penaeus japonicus

Abstract Variations of the total free amino acid (FAA) pool and the content of specific amino acids have been measured in the muscle and hepatopancreas of adult shrimps, Penaeus japonicus , acclimatized at five water salinities: 38, 32, 26, 20 and 14%‰ The FAA content is always higher in muscle than in hepatopancreas at all tested salinites. On the other hand, the hepatopancreas exhibits the highest concentrations of essential amino acids. Two steps in the evolution of FAA content can be observed, the first one regarding decrease in salinity from 38 to 20%‰ and the second one, when salinity goes below 20% ° . The first step can be characterized by a 16% decrease of total FAA content in the muscle and a 36% increase in the hepatopancreas. In muscle, the variations are mainly due to changes in non-essential FAA content, whereas in the hepatopancreas, they are linked to variations in essential FAA content. The other step is characterized by a drastic increase in moisture and decrease in FAA content in both studied organs when water salinity is 14%‰ The total FAA content is about 40% lower in shrimps at 14% ° compared to 38%‰ seawater salinity. During adaptation, the FAA pool (mainly NEFAAs) of muscle seems to be directly related to osmoregulation, whereas in the hepatopancreas, its evolution seems to be linked with energy expenditure and protein synthesis. The results are evaluated in order to elucidate the role of FAA in intracellular osmoregulation and in relation to animal ecology.

Changes in the biochemical composition of tissues in Juvenile Sea bass during forced starvation

Abstract The effects of starvation on sea bass ( Dicentrarchus labrax ) fingerlings (initial average weight 9.5 g) at 19° in sea water were studied. Fish start to die on day 19. Proximate analysis shows that water content increases with starvation time whereas protein and lipid contents decrease. After an initial decline, nitrogen excretion remains stable from day 2 to day 14. Starvation resulted in a reduction of liver, muscle and digestive tract lipids, mainly the triglycerides which are significantly reduced within the first week of starvation. The influence of water temperature on these changes is discussed.

Development of an intensive culture system for sea bass (Dicentrarchus labrax) larvae in sea enclosures

A system for the intensive production of sea bass larvae (Dicentrarchus labrax) in sea structures was developed between 1987 and 1994. In 1994, this system was used successfully for two larval rearing cycles (with 400000 and 420000 2-day-old larvae) at a fish farm. One hundred days after hatching the survival rate was 11%, and the mean weight of fish was 2.5 g. The water temperature varied from 13.9 to 25.4 °C in the cylindro-conical enclosures (40 m3) which were set in the sea. The density of fish larvae at starting time was about 10 1−1. Larvae were fed initially with Artemia nauplii (hatched out on land). Digestive content observations showed that they also fed on natural plankton in the enclosure. Weaning onto microparticles started when the mean length of the larvae reached 12 mm. Temperature variations were largely dependent on the water surrounding the enclosure but the chemical parameters inside were quite different from those of the sea. Many problems solved during the preliminary experiments are discussed, including the control of fouling, but contamination by predators or competitors is still a risk. The natural food web which develops in the enclosure, with the fish larvae as the main predators, seems to be an advantage for larval rearing. The use of such an enclosure system, which is not expensive and is easy to set up at a farm, is discussed.

Nycthemeral variations of ammonia excretion in Penaeus japonicus (Crustacea, Decapoda, Penaeidae)

Abstract Day and night variations (nycthemeral) of ammonia excretion were studied in post-larvae and adults (male and female) of Penaeus japonicus . When the photoperiod was 16:8 ( L D ), ammonia excretion by adults varied only at night, with two maxima: 21.00–23.00 h and 01.00–03.00 h. Ammonia excretion by the post-larvae exhibited variations during the whole day, with four maxima: 21.00–23.00 h, 01.00–03.00 h, 07.00–09.00 h and 13.00–15.00 h. In adults, hourly specific excretion was enhanced during the dark period (× 2). There was no such difference for post-larvae between day and night. The daily specific excretion did not differ between males and females except for some periods of the daily cycle. The daily specific excretion by post-larvae (47.8 μatg NNH 3 NH 4 ·g −1 live weight·24 h −1 ) was about five-fold higher than excretion by adults (10.3 μatg NNH 3 NH 4 ·g −1 live weight·24 h −1 at 23°C). The relationships between behaviour and ammonia excretion variations are discussed.