La fécondité par acte de ponte du listao Katsuwonus pelamis de l'ouest de l'océan Indien a été étudiée à partir de 281 femelles dont les tailles (longueur à la fourche) sont comprises entre 43 et 73 cm et dont les ovaires étaient à un stade de maturité sexuelle avancé. Le liquide de Gilson, utilisé comme agent conservateur et dissociateur des ovocytes, a une action importante et rapide (5 jours) sur le rétrécissement des ovocytes. Des comptages effectués à l'aide d'une cuve de Dollfus sur des sous-échantillons d'ovocytes dissociés, montrent que pour une même période d'activité sexuelle (février), la fécondité du listao du canal de Mozambique est semblable à celle des listaos du sud du plateau des Seychelles. Bien qu'une activité sexuelle du listao soit notée tout au long de l'année, la fécondité individuelle varie d'une saison à l'autre et ce, pour un même secteur géographique. Cette fécondité individuelle par acte de ponte varie de 80 000 œufs pour des femelles de 44 cm provenant de la côte nord-ouest de Madagascar à 1,25 millions d'œufs pour des femelles de 75 cm pêchées autour des Seychelles. La fécondité relative correspondante évolue donc entre 40 et 130 œufs/g de poids de corps. Pour cette espèce, le nombre de pontes successives a été estimé à 4 par an.

Survival of Silurus glanis ovulated oocytes (ova) measured by the capacity of normal development i.e. percentage of normal and abnormal hatched larvae after in vivo and in vitro storage and exposure to sperm activating or immobilizing solutions and urine was studied. In the case of ovulated oocytes left in the ovaries, total hatching and abnormal hatched larvae (in % of hatching) were respectively 74 and 8.2% immediately after ovulation, 77 and 8.6% after 2 h, 54 and 18% after 4 h, and 38 and 50% after 6 h of storage. Four and 6 h stay of ovulated oocytes in ovaries resulted in a significant increase of abnormal hatched larvae (p < 0.01). For the ova stored in vitro, the capacity to undertake a full embryonic development after fertilization was not significantly changed either after 8.5 h at 19 °C or 3.5 h at 25 °C; there was no ova survival at all after 3.5 h storage at 8 °C, 12 h at 19 °C and 8.5 h at 25 °C. There was a significant increase of abnormal larvae after 3.5 h at 25 °C (74%, p < 0.001) and after 8.5 h at 19 °C (37%, p < 0.05). Exposure of non inseminated ova to water buffered to pH 7.0 (5 mM Tris-HCl) to sperm activating solution (17 or 41 mM NaCl, 5 mM Tris-HCl, pH 8.0) or to immobilizing solution (200 mM NaCl, 30 mM Tris-HCl, pH 7.0) resulted in a regular and rapid decrease of their capacity of development; this was 10% of normal hatched larvae within 4 min in water, and within 6-8 min in the NaCl solutions. A similar situation was observed after exposure to urine with a loss of embryonic development of 30% within 3 min. These results indicate that all steps of the whole procedure of gamete collection and artificial insemination should be carried out rapidly as soon as possible after ovulation.

The pursuit of sustainable fisheries requires a broad vision of fishery science as the scientific study of fishery systems. This implies the incorporation into fishery science of research on fishery management, fishing processes, fisher behaviour and the human dynamics of fishery systems. Such research requires (a) more extensive multidisciplinary linkages, with an increased role for economic and social science research, and (b) more day-to-day linkages between people, namely those involved in fishery science and in management, together with fishery stakeholders. This paper reviews potential directions for fisheries research, and suggests a corresponding range of multidisciplinary research priorities, focused on analysis of: (a) the fishery management system, at both strategic and operational levels, (b) fisher behaviour andresponse to regulations, (c) "human dynamics" in fisheries, and (d) fishery systems modelling.

Taking into account that the relationship between metabolic substrate and the characteristics of the diet is essential for understanding the mechanisms associated with the use of the components of a certain food substance, the aim of this study was to examine the metabolic substrate used by Penaeus setiferus, P. schmitti, P. duorurum and P. notialis postlarvae PL 35–40 (35–40 days after metamorphosis) fed purified diets with different levels of proteins (40, 50, 60 and 65%). Oxygen consumption and ammonia excretion were measured in animals in intermoult which had been acclimatized to each diet over a minimum of 5 days. Measurements were taken on fasted (24 h) and fed animals. Oxygen consumption of fasting animals increased with a rise in the proteins of the diet in the four species. In the fed animals, this tendency was observed in P. setiferus and P. notialis, while in P. schmitti and P. duorarum oxygen consumption was a weak relationship, decreasing or increasing with a diet with 50% protein. Both in fasting and feeding animals, the ammonia excretion increased with the increase in proteins in the diet. The O : N atomic ratios of the four species decreased (between 30 and 3), according to increase in dietetic protein : energy ratio, (10.4 to 17.0 mg protein/kcal). The highest value of O : N ratio was observed in P. setiferus (40% of protein requirement, O : N = 24 to 34) and lowest in P. schmitti (60% of proteinrequirement, O : N = 4 to 11), with intermediate values in P. duorarum and P. notialis (50% protein requirement, O : N = 8 to 14 and 13 to 19, respectively). These results support previous research that showed that the omnivorous-herbivorous species, like P. setiferus, use protein-lipids normally as energy source in contrast to omnivorous-carnivorous species such as P. duorarum which use protein preferentially as a source of energy.

In 1983, the European Community (EC) agreed on a system for the conservation and management offishery resources which is based largely on the use of annual total allowable catch (TAC). Nevertheless, the state of many European stocks of demersal species has worsened since 1983. A review of TAC enforcement shows that landings have exceeded TACs to a limited extent for these resources. The contrary is observed for the stocks of pelagic species of which the state has improved although landings have frequently been larger than TACs. This double paradox generates a feeling of limited impact of the TAC system implemented by the EC. To investigate the reasons, the closeness between agreed TACs and scientific recommendations has been examined. The results show that the TAC decision process gives some preference to stability but attention is paid to the scientific recommendations. Finally, the lack of accuracy of predicted changes of fishing mortality in catch forecasts is found to have played a critical part in the failure of TACs to avoid the deteriorations of resources observed in EC waters. It leads to the conclusion that evaluation of risks in the TAC decision process and participation of actors of the fishing sector in risk management are important matters that cannot be avoided if one wants to improve the legitimacy of fisheries management and therefore its efficiency.

Changes in the morphology of the ovary are described during maturation and it is established that it is a homogeneous structure for sampling purposes at maturity stages four and five. Several aspects of vitellogenic oocyte growth and recruitement were examined as criteria to ascertain whether the annual fecundity can be determined in Solea solea just prior to spawning. The first criterion was whether a hiatus develops in the size frequency distribution between the previtellogenic and vitellogenic oocytes just prior to spawning. We were unable to demonstrate this feature in sole from division VIId (N = 5) or IVc (N = 5) but it was present in two out of five fish from division VIIe and all fish examined from division VIIa (N = 5) and IVb west (N = 5). The hiates occurred between 175 and 250 µm (cohort size 25 m) in the size frequency distribution and measured between 25 and 75 µm. Oocyte size frequency distribution from mid spawning and late spawning-spent sole from division IVc showed a hiatus in 9 out of 10 fish which became wider as the residual annual potential fecundity declined. Next the rate of recruitment and growth of vitellogenic oocytes was studied in sole sampled at monthly intervals (July 1993 to February 1994) from division VIId in relation to the start and duration of the annual spawning season. The growth rate of the leading oocyte cohort was 2.73 × 10−5 mm3 per day on 20 September and increased to 3.91 × 10−3 at a mean diameter of 839 µm by 10 February just prior to spawning. However, the observed maximum growth rate, even when adjusted for the positive influence of temperature, allowed little scope for previtellogenic oocytes to complete maturation during a spawning period of 60 days. The recruitment of viltellogenic oocytes was 3013 oocytes per day on 3 August and declined rapidly as spawning approached. In the three months prior to spawning no significant increase was found in the annual potential fecundity. An analysis of a sample of spawning fish from IVc demonstrated that 88% had less than 50% of their predicted potential fecundity remaining in the ovary. The mean batch fecundity was 8 400 (SE ± 13 363) and in conjunction with existing data on spawning frequency and duration gave a realised fecundity close to the potential fecundity. It is concluded that for all practical purposes the sole can be regarded as having a determinate fecundity in all the areas studied.

The regulation of potential fecundity by follicular atresia was assessed in pre-spawning and spawning sole. In ICES areas IV and VII the prevalence of atretic oocytes in pre-spawning fish varied between 0.04 and 0.69 and the relative intensity varied between 0.017 and 0.076. During spawning in division IVc the prevalence of atresia varied between 0.45 and 0.57 and the relative intensity between 0.022 and 0.058. If we assume a turnover rate of 9 days the loss from the potential annual fecundity, during spawning, in division IVc would be 12.4%.

Osmoregulation and salinity tolerance were studied in zoeae 1 and instar IX juveniles of Chionoecetes opilio. In zoeae 1, the lower and upper lethal salinities for 50% of the animals (LS 50) at 14 °C were about 10 and 42‰ at 24 h, 18 and 41‰ at 48 h, 25 and 38‰ at 96 h. In juveniles, the approximate 48 h LS 50 s at 6 °C were 13.5 and 46‰. Both developmental stages are able to withstand relatively ample but brief variations of salinity. Their short-term euryhalinity is discussed in relation to the salinity of their habitat. Zoeae were hyper-osmoconformers. Juveniles were osmoconformers and isoionic to the external medium except for Mg++ which was hypo-regulated. Isosmotic and isoionic regulation in post-metamorphic stages are presumably an attribute of the family Majidae. The pattern of osmoregulation in zoeae 1 and juveniles relate C. opilio to the first of three groups of species previously characterized by their pattern of ontogeny of osmoregulation.

La palourde japonaise présente un grand polymorphisme de coloration de la coquille. Bien que ce polymorphisme soit connu depuis longtemps, son hérédité n'a jamais été analysée. Cette étude a pour but, hormis la connaissance fondamentale du déterminisme génétique des caractères de la coloration, de permettre de produire des individus homozygotes pour la coloration. Ceux-ci pourront être utilisés comme marqueurs génétiques dans des expériences au laboratoire. La coloration est définie par trois caractères, l'asymétrie, l'ornementation et la couleur de fond. Les palourdes à coloration asymétrique sont totalement ou partiellement dépigmentées, à l'exception d'une bande postérieure sur la valve gauche. Les palourdes à coloration symétrique sont pigmentées sur les deux valves. Quatre séries de croisements ont permis l'analyse de différents caractères, Asymétrie et Symétrie, et des ornementations Vague [V] et Zébré [Z]. Les résultats suggèrent que la coloration est contrôlée par au moins deux gènes. Le caractère d'asymétrie est contrôlé par un gène à deux allèles, asymétrie (A) dominante et symétrie (S) récessive. Quelquesindividus asymétriques homozygotes ont été identifiés. Un phénotype Bigarré (Bi), est apparu dans les ségrégations du croisement V × V et des croisements Z × Z. Les résultats suggèrent que Vague et Zébré sont dominants sur Bigarré. Cependant, il existe d'autres ornementations (phénotype 1) et le gène codant pour l'ornementation serait ainsi multiallélique. Le déterminisme de la couleur n'est pas défini. Par contre, les observations montrent que la coloration n'est pas liée au sexe. Dans la majorité des croisements, les proportions observées pour l'asymétrie s'éloignent des rapports attendus selon les lois de Mendel. Cette différence est due à un déficit systématique en individus homozygotes symétriques qui n'a pu être expliqué.

This paper traces the evolution of snow crab fisheries science and its impact on the management of the southern Gulf of St. Lawrence snow crab (Chionoecetes opilio) fishery. This currently lucrative fishery (estimated landed value of more than 125 million Canadian dollars in 1994) has experienced the traditional rises and falls of most fisheries and the resulting socio-economic consequences and sometimes strained relations between the industry and the fisheries management agency, in this case the Canada Department of Fisheries and Oceans (DFO). Of note at this time is the remarkable degree of cooperation that has developed between the industry and DFO since the stock has drastically decreased (1987–1989). Since then the stock has been recovering steadily and is also better managed. The reasons for this are four-fold: (1) arecruitment pulse of small-sized crab occurred in 1988–1989; (2) substantial advances in the understanding of the complex biology of snow crab and the development of an accurate, reliable stock assessment methodology together have provided consistent, reliable and credible advice for forecasting the amount and geographic distribution of exploitable biomass for the upcoming fishing season; (3) the industry leaders worked very hard with their associations to convince fishers that their fishery was in peril and that close cooperation with DFO was the key for the future; (4) the industry and DFO (fisheries biologists and managers) worked as partners to develop a management approach based upon scientific advice to climb out of the trough. The paper also outlines the conundrum that fisheries managers currently face resulting from a combination of a moratorium of the entire Gulf of St. Lawrence groundfish fishery, the consequent pressure from displaced groundfish fishers to enter the lucrative snow crab fishery and an optimistic shortterm but pessimistic longer term forecast regarding snow crab abundance: do we redistribute the wealth; if so among whom and how and for how long?

This paper examines the Canadian experience with quota managed fisheries, reviewing institutional structures and approaches. It begins with a review of management objectives following the extension of jurisdiction and traces the nature and rationale of changes. The specific measures used to achieve objectives are examined from a theoretical and practical perspective. The measures fall into two broad categories: conventional input controls: vessel and gear restrictions; and, output controls: tradable and non-tradable enterprise/individual quotas.

The experience indicates that input controls are largely ineffective in constraining effort. These measures fail to address the common property characteristics of the resource and consequently failed to blunt the incentives for share maximization and increased capitalization. These in turn lead to overfishing and misreporting, thereby undermining management objectives. Output controls in the form of individual tradable quotas fare better in constraining effort. They lead to fleet rationalization and improved quality and flow of raw material to processing facilities. But they may also lead to highgrading and discarding, as quantity incentives give way to unit-value incentives under the rights-based regime.

Some of the carly failures and more recent successes of policy are outlined, lessons are drawn and suggestions made about future directions.

Large numbers of female broodstock (Clarias macrocephalus) are required cach year to produce hybrid catfish which retain the materna1 meat quality of Thai walking catfish and the paternal fast growing and disease resistant traits of the African catfish (C1arias gariepinus). Therefore, diploid meiotic gynogens were induced in Thai walking catfish and their potential use for aquaculture was evaluated. Induction was performed using UV-irradiated sperm of stripped catfish (Pangasius sutchi) followed by either cold or heat shock at 4.5 min after activation. Heat shock at 42 °C for 1 min was the best among various heat shock regimes. Cold shock (7 °C for 14 min) gave significantly higher percentages of meiotic diploid fry (26-41%) than the heat shock (12-26%). Six-month-old meiotic gynogens were all female and showed slightly inferior growth to male and femalc controls. The six-month-old control-males and females and the gynogens were not different in size. Survival of the gynogens (73 ± 8 %) was slightly inferior to the mixed sex control (87 ± 10 %). Gonado-somatic index of gynogens at 1 year of age (5.7%) was slightly inferior to that of the control female (8.8 9%). Therefore, the direct use of all female meiotic gynogens to enhance production of Thai walking catfish, may be doubtful. However, their use for breeding purposes is promising providing that inbreeding depression is eliminated.

Management techniques in two sea scallop Placopecten magellanicus fisheries in Nova Scotia are compared and contrasted. In one, traditional management methods are used to protect the stock from overexploitation. In the other fishery, enterprise allocations in the form of quota shares are used to mimic property rights. Over the past decade, the fleets' reactions to stock conditions have been dramatically different. It is argued that the evidence supports a quasi-property management regime, though other factors are at play as well.

With the aim of improving dry diets for first feeding of Heterobranchus longifilis larvae, the effect of dietary lipid sources on growth rate, survival rate and fatty acid composition of fry from 2 days up to 17 days of age was evaluated. Six feeding regimes were tested: Artemia nauplii which served as a reference, and 5 experimental dry diets differing only by the lipid source. The different oils used for the different experimental diets were the following: cod liver oil, palm oil, copra oil, peanut oil and cotton seed oil. Each diet was tested on duplicate groups of 400 larvae placed in the 40 l tanks of a recirculating system (27-29 °C) and fed to excess six times per day every 4 hours. Separation and identification of the fatty acids of diets, eggs and fry were carried out by gas-liquid chromatography. After 15 days of feeding, survival rates were high for all treatments (71-87%) and did not differ significantly. By contrast, growth rates were largely influenced by the feeding regime. Fry fed with Artemia were significantly bigger (289 mg) than those fed artificial dry diets (79-115 mg). However, it was found that the specific growth rate of fry fed Artemia was superior to that of fry receiving dry diets only for fish of less than 50 mg body weight, indicating that Artemia presents a nutritional advantage only for fry at their youngest stages of development (first 6 days of feeding). Among the artificial dry diets, the best results were obtained with diets containing palm or copra oil, the lowest growth rate being observed with the cod liver oil diet. Peanut and cotton seed oil diets led to intermediate results. The fatty acid composition of the whole fry reflected that of the experimental diets. All together, the results indicated the existence of an optimal ratio between n-3 and n-6 fatty acids for covering essential fatty acids requirement of the fry. Growth rates tended to be reduced by an excess of n-3 fatty acids (cod liver oil) or by an excess in n-6 fatty acids (cotton seed oil) as well. Evidence of the occurrence of HUFA (20:4n-6 and 22:6n-3) biosynthesis are given.