As a first step in assessing the viability of periphyton-based fish production in South Asian pond aquaculture systems, the effects of artificial substrates on development of periphyton and on water quality were evaluated. Earthen ponds (10 × 7.5 m) were provided with an artificial substrate constructed from poles of either bamboo, kanchi or hizol tree branches (1.0 m2 artificial substrate per m2 pond surface). Higher periphyton biomass, in terms of dry matter (DM) (4.9 mg cm–2) and chlorophyll a (11.5 μg cm–2) developed on hizol and bamboo, respectively. Periphyton ash content was higher on hizol (41%) than on the other two substrate types (29%). Protein content of the periphyton growing on bamboo (38% of ash-free dry matter (AFDM)) was 50% higher than that on the other two substrate types. Maximum periphyton productivities of 1.01, 1.38 and 1.03 g C m–2 d–1 were obtained for bamboo, hizol and kanchi substrates, respectively. Taxonomic composition of periphyton showed a rapid development of a relatively stable community with few differences between the substrate types. In total, 56 genera of algal periphyton and 35 genera of phytoplankton were identified. Based on a periphyton productivity estimate of 2.2–2.8 g AFDM m–2 d–1, periphyton alone can sustain an estimated fish production of 5000 kg ha–1 year–1 through the addition of a substrate area equivalent to 100% of the pond surface area.

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.

Surgery procedures were used to implant telemetry transmitters into the body cavity of adult (574–1 033 g) tilapias Oreochromis aureus in aquaculture tanks (4 m2, 1.5 m3, 26.5 ± 0.5 °C, ≥ 5.0 mg O2 l−1) and their effect on fish survival, growth and behaviour was evaluated. Only one out of 35 implanted fish died. With one exception, all fish consistently retained their transmitter until the end of the study (up to 30 months). Healing was faster when the incision was sutured with polyamide monofilament (5–14 days) than with other suture materials, due to tunnelling with atraumatic needles for catgut or fouling of braided silk. In all 10 fish sacrificed after 30 and 50 days, the transmitter had become encapsulated by connective tissue. No infection or damage to the viscera was observed.

The activity of four tilapias (903–1 033 g) equipped with motion sensitive transmitters was telemetered during the recovery from anaesthesia and surgical procedures. All four fish maintained a normal diurnal activity rhythm pattern throughout the study but had low levels of activity during the first 12–24 h. Based on the evolution of their resting posture after surgery, it is suggested that tilapias need 3 to 4 days to completely compensate the negative buoyancy resulting from anaesthesia and tagging.

Deux expériences ont été réalisées pour tester la valeur alimentaire, pour le mâchoiron (Chrysichthys nigrodigitatus), de dérivés de poissons de mer conservés par la méthode de l'ensilage. Le premier essai a concerné des déchets de conserveries de thons conservés par la méthode de l'ensilage acide (3 % d'acide formique). L'hydrolysat, renfermant 66,7 % de protéines brutes (N × 6,25) sur la base de la matière sèche (MS) a été incorporé dans un aliment expérimental en substitution à la farine de poisson sur une base iso-azotée. Les aliments ont été distribués à 6 lots de 50 mâchoirons, d'un poids initial de 34 g, pendant 56 jours à raison de 3 % (sec) du poids vif. Les performances zootechniques procurées par cet aliment sont meilleures, pour ce qui concerne le gain de poids (0,86 g.j−1) et l'indice de consommation (IC : 1,79) et le coefficient d'efficacité protéique (CEP: 1,46), par rapport à celles obtenues avec l'aliment témoin (pas de différence significative). Lors du deuxième essai il a été réalisé un complexe hydrocarboné à base de maïs pour conserver des sardinelles broyées par fermentation lactique. Ce mélange (coensilage), à pH stabilisé à 4,18, et renfermant 35,65 %, de protéines brutes (N × 6,25) en matière sèche (MS), a également été testé contre un témoin farine de poisson dans des conditions expérimentales identiques à celles décrites plus haut. L'aliment à base de coensilage a procuré de meilleurs gains, de poids (0,94 g.j−1, IC (1,77) et CEP (1,61) que l'aliment témoin. Les produits de la pêche ou leurs dérivés conservés par la méthode de l'ensilage acide ou du coensilage biologique apparaissent ainsi constituer une bonne source azotée pour l'alimentation du mâchoiron.