The gulf of Cariaco, Venezuela, is a rather isolated piece of coastal ocean where spatio-temporal variability has been measured. In 1986, three repeated surveys have been carried out in this gulf. The important differences in biomass estimates are attributed to sampling error only. The biological nature of this variability is studied. It is due to a high concentration of the biomass in a few schools and correlatively to the hit or the miss of these large schools, during the sampling. Structural information for predicting them is sought. Also, the number of schools per elementary sampling distance unit (ESDU) and the biomass in each school were measured by echointegration. It is found that there is no clear relation between these two variables. Thus their spatial structures are studied separately, using geostatistics. The number of schools per ESDU is structured in space. Its histogram is not very dissymmetrical. The error variance of its mean estimate is reasonable. The biomass per school is not structured in space. Its histogram is highly skewed. The error variance of its mean estimate is high. The major error variance term on the abundance is due to the imprecision on the estimate of the mean biomass per school. The major quantitative problem is the indeterminancy at the sampling stage of the maximum biomass per school and correlatively the major problem is the characterization of the skewness of the biomass per school histogram. The possibility of using the number of schools as an index of biomass is discussed.

L'évolution annuelle du rapport gonado-somatique (RGS) de mâles et femelles d'atipa (Hoplosternum littorale) collectés mensuellement sur le marais de Kaw (Guyane française) a été comparée au régime local des pluies. Les résultats obtenus sur les femelles ont été comparés à ceux publiés pour Trinidad et Marajo (Brésil). Quel que soit le site, la valeur maximale du RGS, compris, en moyenne entre 11 et 15 selon la localité, coïncide avec le premier maximum pluvieux (juillet à Trinidad, janvier à Kaw, février à Marajo). Cependant, son augmentation débute pendant la saison sèche (mars-avril à Trinidad, août-septembre à Kaw, octobre-novembre à Marajo), après une période « réfractaire » vraisemblablement obligatoire et nécessaire à la reconstitution des réserves énergétiques. L'analyse des données issues d'un échantillon plus restreint prélevé sur une autre localité guyanaise (crique Macouria) confirme ce résultat. Les mesures physicochimiques de l'eau réalisées sur cette dernière localité ont permis de montrer, au cours de la période précoce de la maturation gonadique en novembre, une coïncidence entre l'augmentation de la conductivité (72 à 167 μ/cm2) et celle du RGS des femelles (0 à 6 %) ou des mâles (0 à 0,2 %). Cependant, passée cette période, bien que la valeur de la conductivité baisse (de 167 à 67 μS/cm2 de décembre à janvier), la croissance du RGS se poursuit (6 à 12 % chez les femelles; 0,2 à 0,6 % chez les mâles). La chute de la valeur de la conductivité n'enraye donc pas la poursuite du processus de maturation gonadique.

This paper develops briefly four examples illustrating the use of crustaceans as experimental animals in the field of metabolic and transport physiology. In cells of euryhaline crabs, organic substances such as free amino acids contribute much more than inorganic ions to osmotic adaptation, a feature that is now realized to be of general importance in living organisms. Anhydrobiotic and anaerobically dormant embryos of the brine shrimp Artemia provide very convenient models to study cellular control of metabolic depression. Studies on amphibious crabs have highlighted the constraints imposed upon gas exchange and acid-base balance by the very contrasted properties of oxygen and carbon dioxide in water and in air. Finally, the blood oxygen transport system of decapod crustaceans has been a model of choice to demonstrate the significance of an increased oxygen affinity for adaptation to environmental hypoxia. These examples illustrate the role played in the past as well as the great future potential of crustaceans as experimental animal models for general studies in Comparative Physiology.

In this study an attempt was made to develop a suitable diluent based on the characteristics ofgood quality ovarian fluid of Oncorhynchus mykiss. The resulting simulated ovarian fluid (SOF) was compared with Borax-borie acid buffer diluent and adjusted versions thereof. The composition of al1 these diluents are given in this paper. Maximum fertilization success (81.76%) was achieved when ovarian lluid was employed as a sperm diluent. Spermatozoa showed maximum (34 seconds) forward motility after dilution with Borax 3. The use of diluents in artificial fertilization techniques by trout farmers can help them to increase the fertilization success and also facilitates hatchery procedures and broodslock management.

Goldfish embryos of pre-morula, somite formation, optic vesicle, heart formation and pigment formation stages were tested for cryoprotectant toxicity, using DMSO and glycerol at 10, 12 and 15% concentration. Those that showed 50% or more survival were employed for cold shock test, from 24 to 4 °C at the rate of –1 °C/min. Only embryos at the heart formation stage protected with 12% DMSO showed 60% survival and 35% hatching. A group of embryos of that stage went through a freezing and thawing test to temperatures of –15, –25 and –35 °C. They showed 30, 5 and 2% survival and 12, 3 and 1% hatching respectively.

The dynamics of astaxanthin and canthaxanthin were studied through an 11-month feeding experiment by following carotenoid deposition in male and female rainbow trout muscle, during and after spawning. Carotenoids were analysed by chromatography (HPLC), muscle colour was measured by a colourimeter and visual rank evaluation. In both sexes, a decrease in the muscle carotenoid content was observed at spawning time. The recovery of the muscle pigmentation differed between females and males, but seemed not to be influenced by the type of carotenoid additives in feed. The carotenoid content of the female muscle increased rapidly after spawing, while in the male this increase was slower. Eighteen weeks after spawing, carotenoid concentrations in the muscle of females corresponded to those before spawning, while in males they reached only one third of that amount. Significant correlations were found between chemical analysis, colourimetric measurements and visual rank evaluation.

The diurnal cycle in density measured during acoustic surveys is difficult to investigate quantitatively from the data set of a single survey because the signal depends mainly on the spatial variability and/or horizontal fish migrations. In order to detect the diurnal cycle in spite of the noise due to spatial variability, several acoustic surveys from different tropical countries were combined, after standardization, into a single data base. A diurnal cycle is observed, with the highest values during the night and the lowest during the day. The transition periods are very short (less than one hour). Different hypotheses relative to fish behaviour or to acoustic biases are discussed. Among these hypotheses the lateral avoidance of schools by day and the diurnal change in patchiness seem predominant. Moreover, owing to the extreme skewness of the density distribution the applicability of the Central Limit Theorem is discussed.

The toxicity of sewage sludge to adult and larval Sand shrimp, Crangon crangon, and larval brine shrimp Artemia salina, was studied. Temporal changes in toxicity, ammonia and pH of sewage sludge in seawater were determined. The feasibility of sediment choice bioassays using adult Crangon were examined. The 24 h LC50 of sewage sludge at 20 °C was 0.4% sludge for Crangon larvae, and 10.0% for Artemia larvae. Toxicity to Crangon larvae decreased with decreasing ammonia and increasing pH as sludge decayed over 7 days. In adult Crangon, a dose response with greater variation at < 3% sewage sludge (wet volume in seawater) was found. For adult Crangon at 10 °C, the LT50 at 1% sludge was 80-90 h and 96 h LC50 0.8-1.7% sludge. No clear differences were apparent between 96 h LC5O's in static and 24 h renewal tests. Adult Crangon avoided sediments mixed to concentrations of 6.25% and 10% sewage sludge, but buried at similar frequencies in uncontaminated and 1.57% sludge sediments. In addition to possible chemical effects from ammonia and other sewage sludge components (e.g. metals, organochlorines, hydrocarbons), sludge solids may have physical effects on Crustacea. Bioaccumulation is possible if persistent contaminants occur in the sludge. From estimated field concentrations of sewage sludge, and the results of this and other toxicity studies, lethal effects at sewage sludge disposal sites are believed unlikely. However, further sediment studies (longer-term, life-cycle, bioaccumulation, and mesocosm) are required to evaluate the role of sediment tests in understanding the effects of sewage sludge on benthic Crustacea.

A method for acoustic abundance estimation by horizontal guided sonar of fish schooling close tosurface is presented. The basic principle is to measure the horizontal area of schools in situ, and derive the school biomass subsequently through a school area to school biomass relationship. The application of the method is exemplified through a sonar survey in the eastern North Sea-Skagerrak in September 1990. The areas of recorded schools were measured by the estimate function of a Furuno CSH-70 sonar, and selected schools were captured by purse seine to establish a school-area to school-biomass relationship. In the actual region, the biomass of herrig (Clupea harengus) and mackerel (Scomber scombrus) was estimated to about 90 000 and 43 0000 tons, respectively. The accuracy of the method is discussed and improvements are suggested.

Preliminary studies of freshly collected halibut (Hippoglossus hippoglossus) sperm by light microscopy indicated that sperm motility, i.e. the percentage of motile sperm and the duration of fonvard progressive movement, was optimized under conditions of osmotic pressure ranging between 400 and 1100 mOsmol/kg and pH for 6.5-8.5. The quality of sperm, stored in vitro on ice, deteriorated rapidly within a few hours, a charactenstic particularly evident in sperm after freezing and thawing tests. Studies of several cryoprotectants indicated that halibut sperm could be successfully preserved frozen when diluted with 3 parts extender (sucrose: 150 mM, CaCl2: 1.7 mM, MgSO4: 7 mM, glycine: 86 mM and Tris: 30 mM at pH: 8), 10% of 1-2 propanediol and one part sperm (3:l). Additional studies of the motility of seawater-activated halibut sperm were conducted by dark field microscopy under stroboscopic illumination. These observations indicated that fast forward-moving sperm motility, which lasts 60-70 s, is correlated with propagating waves on the full length of the sperm flagellum with an initial beat frequency of 45-50 Hz which abruptly drops to about 10 Hz after 60-80 s. The beat frequency is blocked by KCN (5mM) and NaN3, (1.2mM), on intact sperm. The flagellum beat frequency of demembranated/reactivated sperm is dependent on the ATP concentration in the reactivation solution.

Cryopreservation of sperm is an important component of genetic conservation programs for fish.However, since fish eggs or embryos cannot be successfully cryopreserved and since the mitochondrialDNA is maternally inherited, the mitochondrial genomes of fish populations are presently not beingpreserved in these programs. One method of obtaining eggs from stored materials would be tocryopreserve embryonic cells that could later be transplanted into female recipient embryos, formingchimeras; a proportion of these transplanted cells would be expected to enter the germ line andsubscquently develop into eggs. The hypothesis of this study is that isolated blastomeres of rainbowtrout can be successfully cryopreserved and thawed. The objective of this investigation was to determine if the rate of cooling or the type of container alters cryopreservation success. Isolated blastomeres in a freezing solution containing 8.7% DMSO were subjected to one of two different cooling rates in either 0.5 ml French semen straws or cryovials. Thawed samples were examined using phase contrat microscopy, wkh cells scored as being either intact or non-intact. In the nonfrozen control group, 85.4%f 7.6 ($\bar{x}$ ± S.D.) of the blastomeres were intact. There was no significant difference between the cooling rates used in this investigation based on the proportion of intact cells, but there was a significant (p < 0.002) difference in the proportion of intact cells between samples frozen in French straws (35.9% ± 16.5) and those frozen in cryovials (19.4% ± 4.9).

One of the main limitations in acoustic stock assessment is fish identification. We propose here a new method for identifying several communities of tropical fish within a surveyed area. This method, called "Acoustic Populations", consists in splitting a study area in systematic regular strata such as geographical rectangles, and calculating for each stratum a set of acoustic parameters that can be easily obtained with conventional acoustic equipment, and have a discriminant power, such as target strength, mean density, confidence interval and dispersion indexes. It is based on the fact that the biological (specific diversity, physiology) and ethological (gregarism, migrations, etc.) characteristics of fish communities have a particular influence on the echoes recorded, which become characteristical and thus are able to discriminate acoustically several populations. An example of application of the method is given for Eastern Venezuela, and the use of the results for mapping, evaluation and stratification of acoustic data is discussed.

Software, MOVIES-B, developed by IFREMER (Institut français de recherche pour l'exploitationde la mer), enables the recognition of echogram features as acoustic detection structures according to spatial-energetic contiguity criteria. These structures (shoals, plankton layers) are described by energetic, morphological, spatial and temporal descriptors. Specifying acoustic detections as individual shoals will allow shoal by shoal echo-integration and may lead to better biomass estimation and shoal species description. The conceptual and operational framework of MOVIES-B is presented in the first part of this paper. The second part presents preliminary work performed in order to assess the feasibility of classification and possible species identification of shoals using MOVIES-B software. This research has studied the data set obtained from four fisheries acoustic surveys, in the Bay of Biscay. The data set is a matrix of 29 descriptors from 13,122 shoals. A limited knowledge of species composition was obtained from trawling. Eight species were captured: Sardina pilchardus, Clupea harengus, Sprattus sprattus, Engraulis encrasicolus, Micromesistius poutassou, Trachurus sp., Scomber sp. and Capros aper. Cluster analysis and linear discriminant analysis were performed on trawled identified shoals data (808 shoals), after a reduction of the space descriptors by a stepwise technique. A partition into 6 clusters was carried out and clusters are described by species composition and continuous variables values. After grouping the six species shoals in two groups, 84% of shoals from the testing data set could be correctly classified using the linear discriminant function.

Echo sounder data were used to investigate the spatio-temporal variability of shoal behaviour in the Bay of Biscay. Data collected from annual surveys were processed using MOVIES-B software in order to mcasure this variability. The software was designed to measure morphological, energetic and space-time distribution descriptors from the acoustic signal received from fish shoals. Two surveys, DAAG 90 and DAAG 91, provided the appropriate characteristics for such an analysis. The survey's objective was to obtain relative abundance indices for the anchovy (Engraulis encrasicolus) biomass in the Bay of Biscay. The surveys were carried out in the same area (southern Bay of Biscay), at the same period (April) within one year interval (1990 and 1991), using the same equipment (vessel, acoustic system, fishing gear) in a multispecies environment. Frequency distributions for every descriptor were obtained and used to describe the acoustic detection of fish shoals. The analysis of frequency distributions of space-time descriptors (year, day-hour and bottom depth) allowed the construction of derived discrete variables, which defined new subsets of detections. The subsets were then described by the continuous variables. A principal components analysis was used to describe the multidimensional data structure and to describe behaviour patterns. The size and external outline unevenness are correlated groups of shoal descriptors, but are independent of the water column shoal position and the degree of internal shoal structure. An important feature is shoal size variability between years. Significant differences in shoal characteristics were found between bathymetric zones of the same region and the pattern was similar between years. This spatial wariability is related to the distribution of different species between bathymetric zones. Although it was not possible to explain size variability between years, this will be necessary to improve shoal characterization. More knowledge about oceanographic conditions, the productivity level and availability of food, predator pressure and accurate identification of shoal speeies is required, in order to study the spatial or temporal variability in size and behaviour of shoals.