Sampling operations are not routinely conducted in France to monitor the landings of bluefin tuna caught by purse seiners in the Mediterranean. The length, weight and age frequencies of bluefin caught by this fleet are predicted based on sale records, length-at-age and weight-length relations, trends in fishing and natural mortality rates, and other ancillary data. The resulting length frequencies are more accurate than those predicted by Liorzou and Bigot (1992) using a simpler algorithm, and are spread more evenly across adjacent size classes. Catch-per-unit-effort (CPUE) was expressed as the numbers of age 2 bluefin caught per successful seine fishing trip in the Gulf of Lions fall fishery. CPUE indices were computed by several methods, and compared to that of the spanish baitboat fishery in the Bay of Biscay. The index trends of the french and spanish fleets exhibit a general increase during 1970–95, but the results do not demonstrate whichof these is the best indicator of juvenile abundance. Complementary surveys are required to determine the temporal and spatial distributions of surface schools and fishing effort, and identify the most reliable index of abundance.

The objective of the study was tu evaluate the capacity of rainbow trout to discriminate diets containing micro-granulated or powdered novel fluoroquinolone in comparison with a positive (containing sulfamerazine sodium) and a negative control (placebo). In a first trial, groups of trout had access to a self-feeder containing the placebo feed for 10 days, and then to one of the four feeds during another period of 10 days. Fish reduced their voluntary feed intake (VFI) by more than 50 % when they had access to the positive control, and by more than 20 % when they had access to feed containing micro-granulated premix. There was no significant decrease in VFI when the fish had access to feed containing powdered premix, but in this latter case, an increase in feed refusals was observed. In a second trial, the capacity of the trout to discriminate between two self-feeders containing different feeds was tested. During a first period of 10 days, all the feed hoppers were loaded with the placebo feed, to determine the feeder preference relative to any dietary-independent factor. In the following period of 10 days, fish had access simultaneously to the two medicated fecds. During a third period of 10 days, a validation of the results was attempted, using the placebo feed or the positive control in one of the feeders. It was shown that trout were able to discriminate between the two medicated feeds and that micro-granulated premix was better accepted than powdered premix. In addition, an increase in feed refusals was observed when the preferred feeder was loaded with feed containing powdered premix. It is concluded that this tested fluoroquinolone could decrease significantly VFI. The powdered premix was more detectable by the fish than the micro-granulated premix and led to some refusals.

The aim of the present study is to test the extent to which different intensities of continuous additional light affect somatic growth and sexual maturation in Atlantic salmon postsmolts in sea cages. Postsmolts (9 200 individuals) were randomly distributed among four commercial sized sea cages and exposed to either natural light or natural light + continuous additional light of low, medium or high intensity from January to June. In May the high light intensity group had a signiticantly higher mean live body weight than the other groups, and at the end of the experiment in June, all groups differed in mean gutted weight. There was apositive logarithmic regression between level of light intensity exposure during night and mean gutted weight. A small proportion of fish matured sexually (after 1.5 years in seawater) in the natural light group, whereas no maturation was detected in the light groups. These results suggests that to affect growth and proportion or maturation in Atlantic salmon by additional light, there might be different threshold values of light intensity.

Gastrointestinal evacuation of inert X-ray dense marker by turbot, Psetta maxima, was followed by use of radiography. Groups of individually tagged turbot aged 1 + years (136.5 g), were held at 16 °C and acclimatized to a feeding period of 4 hours per day. Fish were fed on pelleted feed in excess. The experimental design allowed a test of the effects of handling stress and post-prandial feeding on gastrointestinal evacuation. Repeated handling affected feed intake, but there were no significant treatment effects on gastrointestinal evacuation rate. Fish that ingested large meals displayed higher evacuation rates of markers than fish which ingested smaller meals, but total evacuation time was longer for the fish that consumed the largestmeals. Marker particles started to be voided from the gastrointestinal tract approximately 10 hours following initiation of a meal. and evacuation of marker was completed within 52 hours under the holding conditions employed in the present study.

Wild Atlantic mackerel, Scomber scombrus, were kept in net cages and fed a high energy salmon diet rich in (n–3) polyunsaturated fatty acids for 8 months. Analyses of whole body and muscle were performed at regular intervals on 1 and 2-year-old fish. The percentage of lipid and dry matter increased in whole body and muscle as the fish weight incrcased from catch to market size over the course of the following year. In all groups of fish examined the sum of fatty acids (n–3) as the percentage of total lipid in muscle decreased from 33 to 26%, while the sum of monoenoic acids increased with 10% from 39 to 49%. Vitamin E concentration of muscle increased substantially during feeding. The oxidation status of the fish muscles was very good at the end of the feeding period, with thiobarbituric acid values of less that 3 µmol kg−1. At theend of the feeding experiment large fish to be sold at market were starved for two weeks. Analyses of the nutritional and oxidative state of muscle showed that transport, slaughter and storage did not affect the lipid content or the fatty acid composition. Low and stable thiobarbituric acid values were observed, while vitamin E content significantly decreased during processing and storage at −30 °C, which indicates that vitamin E was an effective antioxidant in mackerel muscle.

This is an overview of the hormones which may be involved in food intake control in fish, and some hypothetical pathways of their action are given based on mammalian knowledge. Most of the observed effects of these hormones may result from four types of mechanisms, each hormone acting by one or several as follows: (1) hormones could have a direct effect on central nervous system centres, associated with food intake behaviour or via vagal afferent neurons; (2) an indirect effect may occur via the gut which slows gastrointestinal transit, thus resulting in stomach distention which activates vagal afferent neurons; (3) they could have an indirect effect, acting directly on intermediary metabolism via glucose, free fatty acids or amino acids mobilization or storage; (4) the last possible pathway is an indirect effect by modifying directly or indirectly secretions of other hormones involved in food intake control. Some of these hormones (CCK, PYY, glucagon, adrenalin) act as short-term factors which regulate meal ingestion and are generally inhibitory factors. On the other hand, other hormones (GH, TH, and leptin) require more time to modify foodintake behaviour, and appear as stored calorie regulators. However, the orientation of hormones to short-term or to long-term action is not always clear as it has been noted for insulin and glucocorticoids, and may depend on the hormonal and metabolite environment.

The capability of turbots to use self-feeders was studied using 3 groups of 100 juveniles. Feeding activity reached a plateau after 20 days. Almost all feeding activity was observed during the photophase, and the acrophase was associated with dawn. The proportion of nocturnal demands was the highest in the replicate with the lowest feed efficiency, suggesting that feed waste was mainly occurring during nocturnal feeding activity. During the last 30 days of the experiment, demands were only rewarded during two periods of 2.5 h.day−1. Feed efficiency was improved and was homogeneous between the three tanks, but the voluntary feed intake was reduced. It is concluded that turbots are able to use self-feeders but they do not adapt quickly, and they are not able to compensate a reduction of feed access by increasing demand activity during the access period.

The incorporation of an attractant mixture by substitution of an equivalent amount of basal dietary mixture was studied in terms of feed intake and growth performance in European seabass juveniles (mean initial weight : 17 g) fed plant-protein rich diets during 21 days. Three diets had as main protein sources; fish meal, or one of two soy protein concentrates (S and E). To the basal mixture of these last two diets, as well as to a corn-gluten based diet, an attractant amino acid mixture was added at a 2.5% level. Daily feed intake was measured throughout the experimental period. Feed intake and weight gain were highest in seabass fed the fish meal based diet. In those fed the soy protein concentrate diets, the addition of the attractant mixture improved growth significantly; voluntary feed intake and feed efficiency were also ameliorated in thesegroups. In terms of growth, feed intake and protein utilisation, lowest values were found in fish fed with the corn-gluten rich diet, supplemented with the amino acid mixture.