Elevage de spionidés (Annélides, Polychètes) en cycle complet

Abstract

Techniques for the laboratory culture of larvae and adults belonging to the “form C” of Malacoceros fuliginosus are described. Larvae can develop under different experimental conditions: • - In stagnant water, without an aeration system: 100 larvae are maintained in 150 cc of sea water. Under these conditions it is important to feed the animals with very small amounts of food. • - In aerated water: 100 or 200 larvae grown in 1.2 l water; bubbles must be large because very small ones are ingested and larvae die after intestinal occlusion. Growth and survival are better than in static conditions. • - In mechanically agitated sea water: 5000 larvae in 12 or 18 l water. At 19°C larval development lasted between 9 and 14 days, depending on diet and rearing conditions. After metamorphosis, sexual maturity was reached in 1 month. For larvae, various kinds of strictly artificial diets were used: • - macrophytic algae ( Padina, Ulva, Enteromorpha), • - lyophilised (Cerophyl) or congealed cereal germ, • - different diets for fish and human alimentation. Most of these diets were ground in a mortar with an organic sand, then filtered through a sieve of 20 or 56 μm, and diluted in sea water. Algae were dispensed according to two different schemes: either a constant amount of food was given every day [between 0.1 and 1 mg/day (dry weight)] or the amount of food was increased over 2 or 3 days (between 0.045 and 0.470 mg/day the last day). In non-aerated sea water, good results were obtained with Cerophyl and Enteromorpha; other diets were inadequate. With air bubbles, almost all diets enabled metamorphosis to take place. In mechanically agitated water and Ulva plus Enteromorpha, over 95% of larvae developed to metamorphosis. The diet ratio varied between 2.3 and 9.4 mg/day. Adults were reared under one of three conditions: (a) non-aerated (one pair in 150 cc), (b) mechanically agitated (3000–5000 individuals), (c) in a recirculating system (several thousand individuals in 100 l). However, attempts to rear large numbers of adults failed. There was always significant mortality, even though numerous cocoons were deposited. Tetramin was the only satisfactory diet for adults. Advantages of agitation are discussed from different points of view: survival, rate of development, nutrition, maintenance of good conditions, and inhibition of bacterial development. A comparison with other techniques of agitation and a review of different inert diets offered to polychaete and mollusc larvae are proposed.