The use of a shoal analysis and patch estimation system (SHAPES) to analyse hydro-acoustic data is discussed. SHAPES was used to detect and characterise sardine schools from four echo integration surveys off the coast of South Africa. Methods of school detection and characterisation, assumptions made and corrections applied to school variables are presented. Measurements of school morphology and internal school features are discussed and compared to other relevant works. Significant relationships were established, both between measures of school morphology and internal density structure. Several variables showed significant differences between surveys. Composite factors derived from principle component analyses showed that morphological variables are the most important school descriptors. No differences in the loading of composite factors between surveys are evident. This suggests an inherent spatial and temporal stability in sardine school characteristics. This fact may prove beneficial for comparisons of school structure between co-occurring fish species and possibly aid fish school identification in the future.

Les caractéristiques biologiques des civelles (Anguilla anguilla) ont été étudiées entre novembre et mars lors de deux campagnes d'échantillonnage successives (1996–1997 et 1997–1998) dans l'estuaire de l'Adour. Une diminution de la longueur (en moyenne de 73,5 à 67,4 mm) et du poids (en moyenne de 3,5 à 2,6 dg) des civelles durant la saison de migration est observée comme sur les autres estuaires. Différents groupes de civelles peuvent être identifiés au cours de chaque saison étudiée. Les variations du coefficient d'allométrie statique et de l'indice de similarité indiquent l'arrivée successive de différents flux dans le bas estuaire. Ces groupes sont bien différenciés lors de la première campagne alors qu'ils se chevauchent dans le temps lors de la seconde. La conjonction de forts débits fluviaux et de faibles coefficients de marée induit des conditions de migration défavorables pour les civelles qui pénètrent en estuaire. Après accumulation des bancs de civelles dans la partie basse de l'estuaire, quand les conditions hydrologiques redeviennent favorables, les bancs mélangés remontent vers l'amont par « vagues » successives, au rythme des marées.

In the Java sea, pelagic fish are exploited by purse seiners. The resource is dispersed and has to be aggregated before being fished. Light is used to reach this objective. The purse seiners are mobile and fish in ‘packs’. When concentrations of fish are found the fishing vessels gather in clusters. The spatial characterization of these clusters provides better understanding of the fishing strategy followed by the purse seiners. A point process approach is used to understand the clustering process and determine the life time of the clusters. The calculation of a density function defines the surface influenced by the cluster and estimates the intensity of the exploitation inside it. Clustering is the mark of the fishing phase that is defined by the significant divergence of the L-function from the Poisson process. In the fishery, such a result is observed when at least 15 purse seiners are gathered. Usually, the fishing phase lasts 4–6 days. The surface covered by the clusters represents a small part (15–25 %) of the surface that is accessible to the fleet. In these areas, the fishing intensity can reach high values (160 vessels × nautical mile–2).

Groups of juvenile rainbow trout were fed to satiation for 10 days after 1, 11 and 21 days of feed deprivation. These fish (initial body WEIGHT = 20 ± 2 g) were previously fed at different feeding levels (0.5 or 1.5 % initial body weight, to satiation) with a high (20.4 kJ·g–1) or a low (16.2 kJ·g–1) digestible energy diet content for 34 days. It is shown that past nutritional history affected growth performance: duration of feed deprivation has a major effect on intake and feed conversion efficiency; previous feeding level has an effect on intake; dietary energy content affected feed conversion efficiency. In addition, an attempt was made to identify some of the metabolic parameters that could be involved in the increase in growth performance during the 10-day feeding period (whole body and muscle protein and lipid, plasma glucose, free fatty acids and triglycerids). Feed intake after fasting does not appear to be driven by body composition but feed conversion efficiency was correlated with the plasma glucose and free fatty acids.

Bahía Magdalena, located on the southwest coast of Baja California Sur, Mexico (24°20'N, 111°30'W), is an important area for fishing of small pelagic fish. The Pacific sardine (Sardinops caeruleus) comprises more than 75 % of the total catch in the bay. Hydro-acoustic surveys were carried out in this bay using a single-beam echo sounder, Simrad EY-200 (200 kHz), during three oceanographic surveys (March, July and December 1996). Results demonstrate that in July more than 75 % of the positive observations (those echograms with more than 100 echoes in the volume sampled) and most of the echo counts were recorded in the 5–10-m-deep layer. During March and December, positive echograms in the upper stratum were below 50 % and most of the echo counts were detected in the lower layer (10–20 m). These results were related to the availability of Pacific sardine to the commercial fleet, specifically to the capture-per-unit-effort. Results support the hypothesis that sardines migrate during late summer and autumn and that a new recruitment occurs during the winter within the bay.

Lagoon fish in New Caledonia are mainly caught by artisanal fisheries and subsistence fishing. Reef fish are the major component of this catch. The present study aimed at estimating these reef fish standing stocks and at finding the main factors influencing the distribution of these fish. Sampling of 904 stations was stratified according to three zones (north, east and west) and three reef types (barrier, intermediate and fringing). Fish communities exhibited bold heterogeneity in their distribution, showing higher biomass (maximum of 447 g·m–2) and total standing stock (43000 tonnes) in the north zone than in the east and west zones. Similarly, observed patterns were dependent on reef types: higher biomass and total standing stock being observed on barrier reefs than on intermediate or fringing reefs. The total standing stocks, which were about 65000 t, were mainly composed of herbivorous fish families such as the Acanthuridae and Scaridae. The differences in the patterns of distribution of species, individuals and standing stocks between reef types may be explained by variations in terrestrial influences and reef morphology, whereas differences among zones were most likely due to accessibility of fishing areas and fishing pressure. The latter is almost non-existent in the north zone, which can thus be considered to be almost unexploited commercially. This most likely explains the high proportion, 77 %, of long-lived species in the biomass of this zone. The results might have implications in management of reefs elsewhere in the South Pacific, for which similar data are only scarcely available.

Eighty-seven two-hour acoustic surveys (radius 0.8 nautical mile, vertical range 0–500 m) around 17 fish aggregating devices (FADs) were conducted in French Polynesia between December 1995 and February 1997. Associated tuna densities were calculated using two different techniques: echo counting when the fish had sufficient distances from each other and echo integration when the fish swam close together (in schools). No acoustic detection of tuna was observed during 27 of the 87 surveys, representing 81 % of all the nocturnal surveys and 15 % of the diurnal ones. The 60 other surveys showed three different classes of aggregations: (1) ‘deep scattered fish’, observed 45 times, (2) ‘intermediate scattered fish’, observed 16 times, and (3) ‘shallow schooling fish’, observed 16 times. Sometimes aggregations of different classes were observed beneath the same FAD. The size of the fish inside the aggregations (determined from target strength values), the distance between the individuals, and the depth of the fish all decreased from ‘deep scattered fish’ to ‘shallow schooling fish’ (100–300 m for ‘deep scattered fish’, 50–150 m for ‘intermediate scattered fish’, and above the depth of 50 m for ‘shallow schooling fish’). Fish densities also varied according to the class of aggregations: 7.3, 26, and 801 fish per km3 on average for ‘deep scattered fish’, ‘intermediate scattered fish’, and ‘shallow schooling fish’, respectively. The highest densities were observed during daytime, while night-time observations indicated a variety of situations, from the absence of individuals to large amounts of fish.

Small-scale fishing produces about half of the total landings of the gulf of Gabès (Tunisia), but still remains very poorly known. Coastal fleet structure is studied through a typological approach based on multivariate analyses of trip catches (principal component analysis, cluster analysis, and partition). Eleven ‘métiers' are defined by combinations of target species, fishing gears and periods: two of them target cephalopods (octopus and cuttlefish) in winter, one targets shrimp with trammels, and eight target finfish in a more or less selective way with gillnets, trammelnets or their combination, with set nets, and with longlines. This study of Tunisian coastal fishery is the first step towards a more thorough understanding of its structure and dynamics, which is necessary for the management of resources and fishing activities.

While the pineal organ in poikilothermic vertebrates consistently influences a number of physiological processes, its precise role, and what controlling signal (hormonal and/or neural) is abolished by its removal, is still uncertain. For this reason, the effect of long-term pinealectomy (PINX) on seasonal growth and reproductive development was investigated in Atlantic salmon, Salmo salar, parr. Mean daytime plasma melatonin level in the control, sham-operated and PINX fish was 35 pg·mL–1 in all groups, while mean night-time levels were 296, 255 and 25 pg·mL–1, respectively, indicating that PINX abolished the natural nocturnal rise in melatonin. Pinealectomy did not influence the incidence or timing of early sexual maturation in the male parr. However, pinealectomy significantly affected growth, its effect being boldly seasonally dependent. Compared to sham-operated and control fish, pinealectomized fish showed significantly lower specific growth rates (SGRs) during the period of lengthening photoperiod up until the summer solstice. Thereafter, corresponding to the season of decreasing photoperiods, the pinealectomized fish exhibited higher SGRs. These results suggest a functional relationship between the pineal organ and somatic growth in the Atlantic salmon, although what controlling signal from the pineal (melatonin or neural) is involved has yet to be determined.

Fish stocks found on lagoon bottoms and near reefs are characterized by a high diversity and heterogeneous habitat which make stock estimation difficult. In particular, it is necessary to combine several methods in order to evaluate the major components of these stocks. The present study aimed at estimating reef fish stocks in the Northern Province of New Caledonia, a region where they represent a major target for the local fishermen. These estimates were based on experimental fishing with handlines and bottom longlines. Handlines were used to assess the stocks near reefs, and longlines for those in areas away from reefs and on lagoon soft bottoms. Handline stations (363) were sampled in three different regions (west, north and east lagoons) and three biotopes (nearshore, middle lagoon and barrier reef). A total of 104 species were caught, the major families being Lethrinidae, Lutjanidae and Serranidae. Species composition and catch per unit of effort (CPUE) varied among regions and biotopes. In particular, the north zone showed characteristics of an unexploited area with very high yields. An increase in CPUE and fish size from the coast towards the barrier reef and with increasing depth was observed in all regions. Correlations between CPUE from handlines and the numerical density and biomass estimates from underwater visual censuses (UVC) performed on nearby reefs were significant. A total of 206 longline stations were sampled in the west and east regions. A total of 80 species were caught, the major families being the same as those caught in stations with handlines with the addition of Carangidae. The CPUE of longlines was significantly correlated with numerical density and biomass estimates made by UVC along the longlines. Stock estimates based on the correlations between CPUE from handlines or longlines and UVC estimates indicate that 90 % of the lagoon stock were found on soft bottoms and near reefs. Reefs, despite biomasses that were five times larger than soft-bottom and near-reef areas, made only a small contribution to total stock. The ratio between density and CPUE was highest for the lowest densities, thus indicating that fishing efficiency increased with density. Comparison of handline catch performed around reefs and UVC data from nearby reefs suggests that there were bold relationships between the fish assemblages of these two biotopes.

Experiments conducted at the Qualark Creek acoustic site on the Fraser River have shown unexpected systematic errors in the split-beam angle measurement. A tethered dead salmon with a target strength of approximately –30 dB was used as a target at 3.7 m range. A signal-to-noise ratio of ~12 dB was observed. This target strength and signal-to-noise ratio are typical in some rivers where migrating adult salmon are observed. The target's location was measured both from the frame used to position the target in the beam and from the acoustic data. Comparison of these two sets of measurements demonstrated a bias that increased with the target's distance off the beam axis. The acoustically measured target locations were closer to the beam axis than the actual locations. Each acoustic estimate represented the mean location obtained after 3 000 pings. Results from a simulation model that includes the effects of random noise on the split-beam angle measurement reproduce the systematic underestimate of these angles. This bias increases rapidly with increasing off-axis target location and decreasing signal-to-noise ratio. The bias has been observed for circular and elliptical beams and the model accurately predicts the magnitude and direction of the systematic part of the angle measurement error in both cases. Results for a circular transducer are used here to illustrate the situation. The presence of this bias can affect measurements of fish density and migration speed. At the low signal-to-noise ratios often obtained in riverine environments, those who use a split-beam system for observation or estimation of fish should be aware of this phenomenon.

The present work examines the usefulness of the combination of multivariate analyses and further one-way analysis of variance in the search for links between causes and effects in heterologous stimulation of spawning in fish. Stimulations with both 20 and 50 μg.kg–1 doses of [D Trp6] luteinizing hormone-releasing hormone analogue (LH-RHa) were effective in inducing and synchronizing spawning of red drum, Sciaenops ocellatus. Oocyte development monitoring using ovarian biopsy allowed treatment injections at different stages of maturation. The influence at stimulation time of female oocyte development state upon further development was shown. An interesting potential of second stimulation, leading to high quality spawns, was established and factors of success were identified. The best conditions for stimulation success were simultaneously late stage of oocyte development characterized by the beginning of oil droplet coalescence, high ovarian homogeneity quoted by the proportion of most developed oocytes in the biopsy sample, and low dose of hormone (20 μg.kg–1) for both first and second stimulations.

Over a 3-year period at the Sukamandi station (West Java, Indonesia), 107 Pangasius hypophthalmus females were selected on the basis of a modal oocyte diameter greater than 1.0 mm and treated with either Ovaprim (n = 97) or hCG (n = 10) to induce oocyte maturation and ovulation. The two hormonal treatments led to similar results in terms of ovulation rate (88 and 90 %), hatching rate (72 ± 25 and 82 ± 11 %) and relative fecundity (171000 ± 73000 and 128000 ± 60000 ova·kg–1, with Ovaprim and hCG, respectively). The latency period between the last hormone injection and ovulation was negatively correlated to water temperature but showed important variations at a same temperature depending on individual females (e.g. between 5 and 11 h at 28–29 °C). The ovulation time was therefore difficult to predict accurately in this species. The assessment of the viability of ova retained in the ovarian cavity after ovulation showed that the process of overripening occurs rapidly in P. hypophthalmus. The overall quality of ova began to decline as early as 2 h after ovulation and, after 3 h, hatching rates decreased and the proportion of deformed larvae increased significantly in comparison to those observed at the time of ovulation. In some individual females this process occurred even more rapidly, with a sharp decrease in hatching rates between 1 and 2 h post-ovulation. The duration of ova survival did not appear to depend on the type of hormone treatment used to induce ovulation (Ovaprim or hCG). For optimized gamete management in hatcheries, it is therefore recommended to check carefully the females for the occurrence of ovulation (between 3 and 11 h after the last hormone injection, depending on water temperature) and to strip and fertilize the eggs less than 2 h thereafter.

This article describes tracking experiments conducted on eleven yellowfin tuna using ultrasonic transmitters in French Polynesia between 1985 and 1997. Nine fish were caught near Fish Aggregating Devices (FADs) while the other two were tracked in coastal areas without FADs. The fish showed different patterns of horizontal movements: tight associations with FADs lasting several days, foraging movements confirmed by simultaneous acoustic observations of prey-sized fauna, movements parallel to the shore, and traveling between FADs. This intra- and inter-individual variety of behaviour might depend on the local environment (prey), and on individual biological differences. The influence of FADs, coastlines, and prey on tuna movements is discussed. The lack of information about the surrounding environment, the internal state of the fish and the recent history of the fish usually prevent scientists from adequately interpreting the observed movements. Ideas for future research to studying tuna behaviour near FADs are discussed.

The effects of dietary medium-chain fatty acids (MCFA) on survival, growth and fatty acid composition of first-feeding carp larvae were investigated in two 21-day feeding trials. In trial 1, one diet CO was supplemented with 10% coconut oil, two diets, M1 and M2 with 1.7 or 4.2% interesterified medium-chain triacylglycerols (MCT), and two other diets T1 and T2 with 1% tricaprylin and 0.7% tricaprin, or 2.5% tricaprylin and 1.7% tricaprin. The five diets were made isolipidic (18% of dry diet) with triolein and compared to a control diet without MCFA. With a low dietary level (1% of dry diet) of caprylic acid (C8:0), final survival and mean weight of larvae fed CO, M1 and T1 were not significantly different from those of control (68 ± 6% and 62 ± 8 mg, respectively). In contrast, with a high dietary C8:0 level (2.5% of dry diet), final survival and mean weight of larvae fed M2 and T2 were markedly decreased (23 ± 2% and 40 ± 8 mg, respectively), without effect of the form of supply. In trial 2, larvae were fed six diets with graded tricaprylin contents (from 0 to 10% in diet). Survival was not significantly affected but growth was decreased by C8:0 levels higher than 2% of dry diet. Fatty acid composition of larval total lipids revealed high levels of lauric and myristic acids in larvae fed coconut oil. Deposition of C8:0 and capric acid (C10:0) was low after MCT feeding, but depended of the form of supply, being higher with pure than with interesterified MCT. Relatively high amounts of C8:0 and C10:0 were recorded in total lipids of larvae fed 10% tricaprylin. It is concluded that high levels of caprylic acid decrease growth but that low levels are well utilised by carp larvae, irrespective of the form of supply.

Measurement of total body electrical conductivity (TOBEC) recently has been used to estimate the body composition of several fish species in a noninvasive manner. The present study was conducted to evaluate the use of TOBEC in estimating body composition of largemouth bass (Micropterus salmoides). A total of 85 largemouth bass weighing 154 to 3245 g were measured for electrical conductivity after which their proximate composition was determined by chemical means. Significant linear relationships existed between the natural logarithm of whole-body ash, lean body mass, lipid, protein, and water content and the natural logarithm of length and/or weight with r2 values ranging from 0.860 to 0.999. Inclusion of the TOBEC value did not significantly improve the prediction accuracy of these models. Equations were developed to allow the prediction of body composition of largemouth bass based on length and weight measurements. Prediction models including only length and weight as variables provided estimates of body components of an independent set of fish that were not significantly different from chemically derived measurements of these components. These models should allow the rapid, nondestructive estimation of body composition of largemouth bass varying in size and condition without the added cost and processing time associated with measurement of TOBEC, although large prediction errors might prevent the detection of ecologically significant differences in body composition. However, with additional data involving narrower fish-size ranges and constant temperatures for the development of prediction equations, TOBEC may improve the prediction accuracy of body composition estimates for largemouth bass.

This paper describes the suitability of a closed recirculation system to study the development of fish larvae in a strictly controlled environment, where only feeding was varied (fed, starved, delayed and late fast treatments). The system served both as an incubator and hatchery. The time variation of physical and chemical parameters together with survival and growth of reared sea bass larvae (Dicentrarchus labrax) were studied over the first month of life. The recirculation design allowed for the maintenance of levels of ammonia, nitrite and nitrate below those cited as responsible for mortality or decreased feeding ability in other marine fish larvae. Almost no larval mortality occurred in the fed larvae from day 9 after hatching. The starved group of larvae showed a sharp decline in survival after 16 days of food deprivation. Larvae for which feeding was delayed until day 13 ceased dying 4 days after food was supplied. Fast feeding on days 24 and 25 had no effect on larval survival. Growth in length was similar during the first 2 weeks of larval life regardless of feeding treatment. Two days of late fast had no effect on larval growth. Growth patterns of fed larvae in this study were similar to those reported for larvae reared in flow through systems. We believe that survival and growth of the reared larvae was a direct function of diet, and that the type of rearing system did not adversely affect these parameters. The rearing design and the results obtained suggest that future nutritional studies of field-collected larvae will benefit from this kind of rearing experiment.