Jean Paul Lagardère

Feeding rhythms and food of Penaeus japonicus Bate (Crustacea, Penaeidae) in salt marsh ponds: role of halophilic entomofauna

Abstract The feeding habits of Penaeus japonicus in aestival, semi-extensive cultivation, were studied in salt marsh ponds of the French Atlantic Coast. A bi-monthly sampling programme was carried out over 3 months: on each occasion, samples were taken hourly over a 24-h period and the stomach contents of a total of 1191 shrimps were analysed. A shift from continuous to nocturnal feeding occurred during the second month of the rearing period (i.e. between 74 and 97 days after metamorphosis). In semi-extensive shrimp culture (from 10 shrimps m−2 at the beginning to 3.4 shrimps m−2 at harvesting), naturally occurring prey were the largest food source throughout the study, despite a daily supply of pellet food. Shrimps appeared to be opportunistic carnivores since they fed on all the salt marsh fauna, with a preference for halophilic insects, especially chironomids. However, a selection of prey, related to their size, was observed over the rearing period. The choice of prey shifted in the following order: zooplankton and harpacticoids (Day0-Day7) — harpacticoids (D7-D27) — chironomids (D27-D62) — macrobenthos and chironomids (D62-D86). Feeding rhythms and food preferences are discussed in relation to data obtained in similar studies.

Changes in the swimming activity of the sole (Solea vulgaris quensel, 1806) in relation to winter temperatures in a saltmarsh: observations using ultrasonic telemetry

Abstract The tracks and the daily activity patterns of four young soles were recorded, by ultrasonic tracking, during periods of different water temperature in the ranges 19–23, 6–9.5, 2.2–5.2 and 0.2–2.2°C. Low winter temperatures significantly reduce fish movement. We suggest that for sole cultivation, water warming systems to protect the fish from potentially lethal temperatures should be started when a water temperature of 5°C is reached in the saltpond.

Influence du niveau sonore de bruit ambiant sur la croissance de la crevette Crangon crangon (Linné, 1758). Resultats preliminaires

Abstract The growth of C. crangon is examined in connection with the level of ambient noise. The building of a soundproof box permits the rearing of shrimps in acoustic pressure conditions close to those of their natural biotope, i.e. 10–15 dB μbar −1 quieter, in the frequency range 50–500 Hz, than laboratory culture conditions. The decrease in sound pressure significantly increases the growth of shrimps, maintains their food consumption and, at the same time, diminishes their aggressiveness.

The effects of illumination, temperature and oxygen concentration on swimming activity of turbot Psetta maxima (Linné 1758)

Abstract Swimming activity of turbot was recorded in a 250 m 2 earthen pond by acoustic tracking and was analysed in relation to illumination, temperature and oxygen concentration. A pronounced diurnal rhythm was found, with greater activity at night. Illumination interacted with both temperature and dissolved oxygen concentration in determining swimming activity. Activity increased with temperature, particularly above 20 °C at night, without a clear effect of oxygen concentration level ranging between 4 and 9 mg l −1 .

Sound production mechanism in carapid fish: First example with a slow muscle

Fish sonic swimbladder muscles are the fastest muscles in vertebrates and have fibers with numerous biochemical and structural adaptations for speed. Carapid fishes produce sounds with a complex swimbladder mechanism including skeletal components and extrinsic sonic muscle fibers with an exceptional helical myofibrillar structure. To study this system we stimulated the sonic muscles, described their insertion and action, and generated sounds by slowly pulling the sonic muscles. We find the sonic muscles contract slowly, pulling the anterior bladder and thereby stretching a thin fenestra. Sound is generated when the tension trips a release system that causes the fenestra to snap back to its resting position. The sound frequency does not correspond to the calculated resonant frequency of the bladder, and we hypothesize that it is determined by the snapping fenestra interacting with an overlying bony swimbladder plate. To our knowledge this tension release mechanism is unique in animal sound generation.