A holistic perspective of the last 150 years of studies in ocean biology reveals two distinct scientific activities. The first involved scientists in many expeditions from the "Challenger" in the 1870s to the Indian Ocean Expedition in the 1960s. These studies ended with what Ray (1970) has called the "Marine Revolution". This was caused by the need for marine biologists to pay much more attention to practical problems of fisheries, pollution, undersea mining and in particular the biology of the 200-mile economic zone which was established by many maritime nations in the 1970s. The new biological science of the oceans moved from largely descriptive ecology into the field of dynamic processes, holistic models, ocean monitoring and networking of different national and international organizations. Further progress in the biological sciences is needed in these areas, particularly in determining the canying capacity of the seas and oceans and the ecological consequences of removing manne species of fish from the oceans as part of the annual industrial harvest. These problems are only likely to be solved by a consideration of the properties of entire ecosystems, which are often different, to that expected, from the sum of the determinate parts.

Using examples, we discuss some aspects of surplus production models. Although the precision of some parameter estimators may appear to be good, the strong asymmetry of confidence intervals and the large impact of the choice of a given formula on those estimators go against this feeling. Models are often formulated with inference to the biological background, but giving a biological meaning to (the estimates of) the parameters may be very dangerous. Fishing effort standardization does not lead necessarily to useful results for management. The fleet dynamics, per se, may not allow equilibrium States. In the context, of general frameworks, where the evaluation of the resource is not the unique objective, surplus production models may be however very flexible tools for fishery analysis, with low parameter requirements.

Differences in Mediterranean fish communities of two rocky coastal areas, one inside an integral marine reserve and the second outside the reserve, near Banyuls-sur-Mer, France, were compared using underwater visual census after a 12-year interval. In 1980, the community structure in and outside the marine reserve was studied at two depths (Bell, 1983). In 1992, We used the same methodology to assess if variations occurred in this fish community between these two samplings. In both 1980 and 1992, water depth affected the relative abundance of fish communities and the number of species was roughly maintained in both sites. However, there were several other important qualitative and quantitative variations in the fish fauna over this period: (1) The abundance of species has decreased in the integral reserve whereas it has been maintained outside the reserve; (2) Nine species are more abundant in the integral reserve and nine others are more abundant outside the reserve. Among the species vulnerable to fishing, such as Labrus merula, Symphodus tinca, Mullus surmuletus, Diplodus sargus, D. vulgaris, Scorpaena porcus, Oblada melanura, 6 of them are more abundant inside the integral reserve and 4 others are more abundant outside; (3) The demographic structure of vulnerable species inside the reserve has changed: only the proportion of large fish (30 to 40 cm length) compared to medium (15 to 30 cm) and small (0 to 15 cm) fishes was higher in the integral reserve. The prohibition of recreational and professional fisheries and scuba diving has the fish community in the integral marine reserve in 1992 enhanced less than in 1980. The impoverishment of the fish density in the integral reserve between these two periods is difficult to understand in regard to the stability of the fish density outside the reserve. These results stress the need for a more regular and more extensive survey of the fish assemblage in and around the marine reserve of Cerbère-Banyuls

Chrysichthys nigrodigitatus and Heterobranchus longifilis are two commercially important African catfish species that have been studied for their reproduction and breeding possibilities in the lagoon waters of Ivory Coast. C. nigrodigitatus is characterized by an annual reproductive cycle with a vitellogenesis period from March to June. The reproductive season coincides with the short rainy season which is characterized by lower water temperature and salinity at the beginning (September) and by a progressive rise of these parameters at the end of the season (November). The previtellogenic oocytes enter vitellogenesis at an average diameter of 320 μm. This initial oocyte stock is reconstituted progressively as soon as the spawning is achieved and lasts for a period of approximately 3 months. Fully vitellogenic oocytes reach an average diameter of 2.4–2.8 mm by the end of June. The maturation is possible only if a male and a female are confined in artificial spawning receptacles. Maturation and spawning generally occur within the following 3 to 5 weeks for 30 to 80% of the females. When the non-spawning females are kept in the nests they maintain fully vitellogenic oocytes for 3 months with a continuous atresia of the larger oocytes, while the ovaries of the non- spawning females, placed out of the receptacles, exhibit a complete atresia of all the vitellogenic oocytes. After an HCG-induced ovulation, a new reproductive cycle of H. longifilis can be achieved in less than a month. The previtellogenic oocytes enter vitellogenesis at an oocyte diameter of about 380 μm and become fully vitellogenic after 15 days (1.2–1.6 mm in diameter). If maturation is not artificially stimulated the females remain at the same stage of vitellogenesis while larger oocytes undergo atresia and are continuously replaced by growing vitellogenic oocytes.

Historically, nation-state level fisheries management has relied primarily on the disciplines of biology, ecology, and to some extent economics – usually in some combination, and with varying degrees of emphasis and success. Recently, as an increasing number of fisheries have begun to experience severe declines there has been increased interest in how social scientists might help to address some of these problems. In managing fisheries, it is humans who must be understood and managed. Furthermore, some managers have begun to question the view of biological conservation as the primary goal of management, sceing economic and social goals as equally important. Social science studies of fisheries indicate that not all members of a given user group operate in the same way, or have the same impact on marine ecosystems. People's behavior is often influenced by family, community, and other sociocultural variables in addition to economic and cological considerations. Using the perspectives and methodologies derived froin disciplines such as anthropology and sociology, fisheries managers should be able to develop policies which integrate and balance economic, social and biological objectives. Management systems which are more compatible with broad user group values should result in higher coinpliance and reduced enforcement costs. An overview of recent social science research pertaining to fisheries management is discussed, and examples presented on the relevance of social science information in crafting successful management regimes.

An analysis of statistical data available in eight glass eel fisheries distnbuted over the French Atlantic coastline is used to define the upstream migration dynamics of Anguilla anguilla in estuaries. The CPUE (Catch Per Unit of Effort) data reveal three different types of seasonal trends that reflect different migration kinetics. The recruitment abundance is studied compared to the salinity of the estuary. The first two types of trends correspond to years of high recruitment andor of reduced fishing effort. In brackish estuarine zones, the abundances then follow a symmetrical curve, with a peak in JanuaryFebruary. This time course is due to the passage of a wave of migrants. Further upstream, in tidal freshwater zones, the abundances follow an asymmetrical curve which may describe the progressive accumulation of eels between November and March/April. When recruitment is low andlor the fishing effort is high, CPUEs vary during the season following a plateau curve, with values staying more or less constant between November and March. This latter trend represents a balance status between immigration and capture. In this case, abundance indices can only be established with total catches. The curves are explained by the migration behaviour of glass eel which exhibit a resting phase in brackish zones and an accumulation in tidal oligohaline zones. These results have direct consequences particularly for the determination of recruitment abundance indices.

Using the example of the New England Regional Fishenes Management Council and its attempts tu manage the fisheries in its area, this paper argues that disferences in the way Nature "operates" constitutes a major source of divisiveness between, on the one hand, those members (and other managers in, say, government) who use linear modeling systems and, on the other hand, the majority of those in the commercial fishing sector who, intuitively, have cast nature in those non-linear terms currently being explored in the Chaos paradigm. Since these two different models have not been explicitly addressed, there is a history of members on each side accusing those on the other of bargaining in poor faith and lacking an adequate understanding of the resource. The thesis of the paper is that making explicit these underlying cognitive modes would provide more "common ground" for addressing management problems in such co-management arenas as the fishery management councils and elsewhere.

Dramatic changes in the Lake Victoria (East Africa) environment were observed after the introduction of the Nile perch (Lates niloticus) in the 1950s. An extraordinary spectrum of endemic haplochromine fishes, a result of intralacustrine adaptive radiation was reduced by massive species extinctions (ca. 65%) due in part to predation by Nile Perch. Such an abrupt destruction of natural diversity has never before been documented by scientists. Lake Victoria's haplochromine species flock comprised upwards of 400 species (5% of the world's known freshwater fishes), encompassing a remarkably wide trophic spectrum and constituting 83% of the lake's total fish biomass. The lot evolved in an isolated part of the Nile system since the formation of the lake basin about 750 × 103 years ago, but quite possibly as recently as 14 × 103 years ago, when most of the lake dried up. More than 50% of the haplochromine species (by number) were phytoplankton-zooplankton-detritus consumers; 55% of their biomass were detritivores and 27% zooplanktivores. The piscivore Nile perch (Lates niloticus) was first introduced into Lake Victoria in 1954. It underwent rapid population expansion in the 1980s, accompanied by haplochromine decline. Consequently, phytoplankton and detritus consumption by fishes was reduced. The biomass of the endemic Cyprinidae Rastrineobola argentea increased, as did its fishery, and predation pressure on zooplankton was therefore intensified. The population of the prawn Caridina niloticus became very dense, mostly in deep waters. The fishery and fish industry were altered fundamentally. Limnological changes suggesting eutrophication have been observed since 1960: hypolimnetic anoxia increased and the period of extensive vertical mixing was restricted to about one month per year; phytoplankton productivity increased and shifts from diatom to blue-green dominance occurred. Increased inputs of N (from the 1920s) and P (from the 1950s), induced through precipitation and human activity in the catchment area (agricultural and urban developments, deforestation, etc.) and high water levels accompanied by decline of available silicon, have persisted. Both top-down (Nile perch piscivory) and bottom-up (nutrient changes) influences enhanced eutrophication. The concurrent system changes in nutrient dynamics may have contributed an additional impact to the extinctions of haplochromine fishes.

La gestion de la reproduction du saumon atlantique nécessite généralement un transfert des géniteurs en eau douce avant la phase finale de la maturation sexuelle pour obtenir des gamètes de bonne qualité. Afin d'analyser l'impact de l'environnement marin, des géniteurs de saumon atlantique âgés de 2 ans (2+) ont été, soit maintenus en mer en cage (EM) jusqu'à la période de reproduction, soit transférés en eau douce (ED), en juin (EDP) ou en octobre (EDT). Les dates d'entrée en spermiation et d'ovulations ont été notées grâce à des observations hebdomadaires. La qualité des gamètes a été évaluée par le taux d'embryonnement au stade œillé après insémination de lots de 200 œufs par du sperme dilué à 10−3 avec du DIA 532®. Les femelles EDP et EDT ont ovulé entre novembre et décembre alors que les femelles EM présentaient un retard et un étalement des ovulations : 67 % des femelles EM avaient ovulé à la fin de l'expérience en avril. La fécondité relative des femelles EDP était significativement plus basse que celle des femelles maintenues en mer au moins jusqu'à l'automne. En dépit des cinétiques d'ovulation et des osmolantés des liquides coelomiques plus élevées, les œufs de femelles EM présentaient une qualité similaire à ceux des femelles ED lorsqu'ils sont utilisés moins d'une semaine après l'ovulation.

Les mâles ED et EM présentent des courbes similaires d'entrée en spermiation. Les spermes des mâles EM présentaient une qualité hétérogène et en moyenne médiocre. L'osmolarité des plasmas séminaux des mâles EM était significativement plus élevée (347 ± 13 mOsmol/l pour EM contre 265 ± 23 mOsmol/l pour ED). Les spermes EM de mauvaise qualité donnaient des résultats médiocres quelle que soit l'osmolarité des dilueurs d'insémination utilisés et comprises entre 150 et 450 mOsmol/l. De plus, aucune relation n'a été mise en évidence entre l'osmolarité individuelle des plasmas séminaux et la mauvaise qualité des spermes. D'un point de vue appliqué, l'osmolarité du plasma séminal ne peut être retenue comme critère qualitatif et le vieillissement des ovules après ovulation dans la cavité abdominale doit être strictement évité pour les femelles EM.

The aim of this study was to monitor the reproductive cycle of female Heterobranchus longifilis under tropical pond conditions in order to optimize controlled spawning. Three experimental groups were set up: The first group (I) consisted of adult females transferred from their natural habitat to ponds. The second experimental group (II) consisted of breeders that adapted to husbandry conditions for at least one year. The third set of females (III) was produced under hatchery conditions. Females of the natural population served as controls. Over a one year period blood samples were taken from the individually marked females on a biweekly basis. If ripe eggs were found at the sampling time, females were stripped, the eggs were fertilized and hatched artificially. None of the feral breeders that were transferred to ponds during their natural breeding season could be stripped during that year. The breeding season of both groups II and III started in February. Seasonal changes in egg output showed a maximum between April and July. Egg production of group III was generally higher. The time interval between two strippings of the same female was 6 weeks. Viable eggs were obtained from the adapted feral breeders until August, whereas the breeding season of the hatchery-raised females extended to October. Two thirds of the hatchery-raised females were stripped four or more consecutive times. Throughout the entire season high hatching rates of normal larvae were obtained. Seasonal profiles of the gonadal steroids testosterone and estradiol-17β reflect the annual changes in sexual activity of female Heterobranchus longifilis in tropical pond culture, exhibiting maximum values during the breeding times of each group and being lowest during resting periods.

This work examines the effects of constant long and short days on the hormonal profile of plasma 17β-oestradiol (E2) levels and the ovarian vitellogenic events, as well as on the fecundity, time of spawning and egg quality of sea bass. Constant short days first administered in April advanced spawning (by 45 days on average) whereas exposure to constant long days from the same date induced a delay (averaging 38 days) compared to controls reared on an ambient light regime (Lat. 40°N). These light regimes produced shifts in the profiles of plasma 17β-oestradiol and in the percentage of the vitellogenic oocytes according to the spawning time of the respective groups. Relative fecundity of the short day group was similar to controls (257,000 versus 230,000 eggs/kg spawned female, respectively). However, in the long day group, relative fecundity was reduced to one half that of control fish (124,000). Plasma oestradiol showed a bimodal pattern under long days and vitellogenetic and atretic oocytes were present for a longer period (6-7 months compared to 4-5 months in controls). In summary, in this paper we describe, for the first time in the sea bass, the effect of constant photoperiod regimes on the 17β-oestradiol plasma profiles, the timing of spawning and the quality of the eggs.

For last 20 years, the fish communities in the Central Delta of the Niger River have been subjected to: (i) two drought periods in 1973 and 1984, (ii) a dramatic increase of fishing and, (iii) the building of an electric-power dam in 1984. At different levels, these various factors modified the biological cycle of the fish which are adapted to the former hydrological cycles of the Niger and the Bani rivers. The Sahelian drought is responsible for a decrease in both flood duration and of the inundated area of floodplain which varies from 20 000 km2 to 5 000 km2. From 1968 to 1989, fish landings declined from 90 000 metric tons to 45 000 metric tons. During the same period, as fish catches fell, yields per hectare increased from 40 kg in 1968 to 120 kg in 1989. This phenomenon is linked to the decrease of the average age of the fish (69% of fish catches are under one year old) in response to the increased fishing mortality and natural mortality which is higher during the drought period. The increase in fish productivity is characterized by a depletion of species such as Gymnarchus niloticus, Polypterus senegalus, Gnathonemus niger, whose reproduction are linked to the floodplains and of species like Citharinus citharus and Clarotes laticeps which visit frequently flooded areas. Concurrently, families such as the Cichlidae or Clariidae, which are resistant to low oxygen concentration, increase. Species which are under one year old at first reproduction and have several spawning periods per year, are the more abundant in fish communities.

Fisheries management in the future will require that biological assessments be combined appropriately with operational, social, and economic considerations toward effective management of complex fisheries systems. This is not currently being done in fisheries management because of: (i) the lack of a conceptual and organizational framework for integrated and participatory decision making, and (ii) the lack of more appropriate methodologies for dealing with diverse sources of information, interdisciplinary objectives, and the inherent uncertainty of these systems. An integration of traditional "fisheries science" with other aspects of "fisheries management" and the field of "management science" in a new discipline of "Fisheries Management Science" is proposed. FMS is defined as "the rigorous application of the scientific method of problem solving in the development of strategic alternatives and their evaluation on the basis of objectives that integrate biological, economic, social, and operational factors into management decision making". Management science or operational research provides guidance in methodologies for complex decision making and problem resolution. A multidisciplinary decision framework is proposed involving the following key steps: (1) specification of quantifiable objectives and constraints; (2) modelling of the expected multicriteria performance of a range of proposed management decisions; (3) risk assessment through descriptions of the expected variability in performance measures; (4) risk management through analytical evaluation of risk and ranking of alternate solutions; and (5) continuous monitoring and improvement of past decisions including deviations from expected performance and corresponding adjustment of future alternatives toward achieving strategic objectives.

The need for a better understanding of the role of biodiversity in the functioning of aquatic ecosystems has been raised recently by several authors. If the question is not entirely new, its formulation is. It is therefore the opportunity to re-examine the pool of data already available in order to discuss some results that may be relevant for that purpose, while some major ecological questions have been identified. The top-down view argues that the effects of fish predation cascade down the trophic chain and are responsible for controlling the state of the entire ecosystem. The influence of fish predation on prey assemblages (prey selection, ontogenic shift) has been fairly well documented by various studies of African fish. They are also challenging subjects for studies of resource partitioning, a well documented example being given by zooplanktivores in Lake Turkana. The principle of cascading trophic interactions has been documented in Lake Victoria, after the introduction of a top predator, Lates niloticus. Another striking example is that of Lake Nakuru where the introduction of a tilapiine resulted in a substantial increase of bird diversity, by the extension of the food chain to fish-eating birds. This introduced tilapiine may be considered as a keystone species, but this concept is questioned. A possible origin of fish biodiversity is adaptive radiation, that is to say the differentiation of species in morphology and resource use through competition. The cichlid flocks of the African Great Lakes where hundreds of rather similar species coexist, provide one of the best known examples of adaptive radiation. The question of niche overlap and functional redundancy has been raised and various studies have been conducted in the East African Lakes. The role of rare species has also been questioned. They may provide an insurance of ecosystem stability, which means that the more stable ecosystems in terms of key functions are those richest in species. In fact, in many large Nilo-Sudan river basins, there are apparently several groups of species which are able to replace the current assemblage when it experiences new ecological situations. Finally, the question has been raised as to what extent patterns of biodiversity are important for ecosystem productivity. The cornparison of data for four African lakes shows no relationship between fish diversity and fishery production, and species richness does not appear to be a major determinant of basic production trends. At present we have only anecdotal, sometimes controversial, evidence of the role of fish diversity on the functioning of African freshwater ecosystems. We need to improve this knowledge on the importance of biodiversity in order to convince decision-makers that fish biodiversity needs protection.

In captive Heterobranchus 1ongifilis females, oocytes maturation and ovulation are induced by a single injection of human chorionic gonadotropin (hCG) at a dose of 1.5 I.U./g body weight. In the present study, three experiments were performed in order to specify the timing of ovulation and the effects of varying latency period on the quantity and quality of the collected ova. The ova quality was estimated by hatching percentage and proportion of deformed larvae obtained after artificial fertilization. The results showed that, in an individual female, ovulation of postvitellogenic oocytes is not synchronous and takes 3 to 4 hours to be completed, between 7–8 h and 11 h after hCG injection at 30 °C. The quantity of ova that could be collected by handstripping increased with the latency period, from 18,000 ± 12,000 to 72,000 ± 29,000 ova per female at 8 h and 11 h after injection, respectively. However, the first ova obtained (8 h after injection) were of good quality (94% hatching) and showed no signs of incomplete final maturation. Eleven hours after injection, the percentages of ovulated oocytes within the whole ovarian population of postvitellogenic oocytes were high in all the females, being generally around 90%. After ovulation, aging of ova occurred rapidly: the proportion of deformed larvae increased significantly (from 4 to 20%) 2 h after completion of ovulation and, 4 h post-ovulation, hatching percentage dropped from 92 to 36%. In H. longifilis, the optimal latency period can be defined as the time, from injection to stripping, allowing the best compromise between quantity and quality of ova released. This latency period was found to be 11 h following hCG injection at 30 °C, and corresponds approximately to the completion of ovulation.

Fisheries can be characterized as a network of interactions between natural and social systems, and thus should be viewed as complex, dynamic systems. Due to the multiplicity of components and processes, the involvement of various disciplines is required to understand the inter-relationships within and between the systems, and more so to adequately address management issues that typically affect several elements in the systems. To be successful, multidisciplinary approaches require mutual understanding of the perspectives, concepts, vocabulary and methods held by various disciplines, and agreement on the objects to be studied in common. In that spirit, at framework is suggested whereby fisheries systems are decomposed into related sub-systems that can be recognized by both Social and Life Sciences. Some key concepts attached to cach module and to its interactions with the others are identified, and may be starting points for dialogue and common undertakings by various disciplines, with a view to improving our understanding of the dynamics of the whole system.

This work describes the application of a homologous radioimmunoassay (RIA) in the measurement of plasma and pituitary growth hormone levels of tilapia maintained at 20 and 26 °C, using recombinant tilapia growth hormone (rtiGH). RIA sensitivity (ED90) was 0.08 ng/ml and ED50 was 0.62 ± 0.02 ng/ml. Intra- and inter-assay coefficients of variation were 3.3 and 10.6% respectively, for a plasma sample of 1 ng/ml of tiGH. Mammalian or salmonids growth hormones, thyrotropins or tilapia prolactins did not show cross-reactivity with rtiGH antiserum. Plasma and pituitary extract of Oreochromis niloticus gave inhibition curves parallel to the rtiGH standard curve without interaction with serial dilutions either of tissue extracts or plasma from hypophysectomized tilapia. Pituitary extracts from other cichlid fish showed parallel competitive binding curves. Pituitary extracts of perciform fish exhibited a lower affinity to anti- rtiGH serum, while extracts of species from more distant families showed only negligible cross-reactivity or none at all. The effects of water temperature on plasma concentrations and pituitary contents of GH were investigated in tilapia acclimatized to 26 and to 20 °C. Measurements have been performed at the beginning and at the end of a two-week experiment. Whereas in fish from colder water plasma GH mean values were decreased, only a similar tendency was observed in pituitary GH contents. These results emphasize the hypothesis wich reports that the increase of growth with temperature is, at least in part, controlled by GH.