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.

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.

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.

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.

The gametogenic cycle and the reproductive effort of the blacklip pearl oyster, Pinctada margaritifera, cultivated in Takapoto lagoon were studied for a 1-year period (March 1997–April 1998) by bimonthly observations of gonadal sections, dry tissue weights and gonadal index in a population of pearl oyster composed of three age-groups. Pearl oysters attained sexual maturity in the end of their first year (height ≈ 40 mm), implying that P. margaritifera is a late-maturing species in comparison with other Pteriidae. This species was also confirmed to be a marked protandrous successive hermaphrodite in culture, with 100 % of males at first maturity and 75 % in older pearl oyster (height > 120 mm). The general pattern of gametogenic activity, fairly synchronous in both sexes, was comparable with that of other tropical bivalves: reproduction occurs continuously throughout the year with a maximal activity during the warm season (November–May). No resting period was observed. Quantitative growth data showed that P. margaritifera exhibits an annual synchronised polymodal spawning pattern, with two spawning peaks in age-group I (height ≈ 70 mm) and five in age-groups II (height ≈ 100 mm) and III (height ≈ 120 mm). Spawning was sometimes incomplete, nevertheless a clear relationship between gamete production (PR, g) and size (height H, mm) was obtained: PR = 5.26 × 10–7 H2.91 (R[sup2 ] = 0.99, P < 0.05). Estimation of PR was used to calculate the annual reproductive effort in P. margaritifera. Reproductive effort (%) was similar to those calculated for temperate species and showed a progressive increase with the age of pearl oyster, from 7 % in age-group I to 38 % in age-group III. This study showed that, in a fairly stable tropical environment such as the Takapoto lagoon, P. margaritifera is a multiple spawner, which uses an opportunistic reproductive strategy, allowing investment, all year around, of any surplus energy into gamete production. Surplus energy is ensured by the high pumping rates developed by this non-symbiotic bivalve to succeed in low seston conditions.

Whitish parasite-like bodies (PLBs), 0.5–2 μm in size, were detected within the pearl bag of some grafted pearl oysters, Pinctada margaritifera, from Takapoto island (French Polynesia). Histological and ultrastructural investigations have revealed that these bodies consisted of lamellar organic material locally secreted by some epithelial cells of the pearl bag. The fine structure and the formation of these bodies are described. The causes of this abnormal secretion of organic mater, which actually corresponds to periostracum, are not presently known. No parasite nor infectious micro-organism was found associated with the PLBs.