In vitro fertilisation and larval development of a population of Lumbrineris (Scoletoma) impatiens (Claparède) (Polychaeta, Lumbrineridae) of the Gulf of Naples (Italy) in relation to aquaculture

Abstract

Summary Observations on in vitro fertilisation and larval development in a population of the polychaete Lumbrineris (Scoletoma) impatiens (Claparède, 1868) (Lumbrineridae) from the Gulf of Naples (Italy) were obtained in a research programme aimed at developing rearing techniques for aquaculture of this worm. This species is indeed collected for commercial purposes from the shallow sandy bottoms of the Gulf of Naples being used as bait for recreational fishing (“red bait” or “Neapolitan arenicola”). Adult worms were collected and reared in controlled conditions in the laboratory. Mature males and females were monitored for the maturation of eggs and dissected for the collection of gonad products. The morphology of mature spermatozoa is that of a typical “ect-aquasperm” type: the nucleus (2.5 μm long) is sub-spherical, and the acrosome has the shape of a flat dish with a crenulated border. Eggs (average diameter 250 μm) showed a shift in colour from a pale green to yellow during maturation. Yellow eggs are also characterised by a lower specific weight, probably due to a higher yolk content. For in vitro fertilisation, mature eggs were rinsed three times in filtered seawater (0.45 μm), collected on a 100 μm net, then pooled with mature sperms in Petri dishes to allow fertilisation. The rinsing procedure is essential for the success of fertilisation, since eggs are covered by a thick layer of dense mucus. After 90 min, fertilised eggs were collected by Pasteur pipettes and placed in vessels in clean seawater at a density of 1 embryo ml−1 of seawater. The development of larvae was followed. In 24 h a protrochophore stage was produced, embryos were reared thereafter at a temperature of 19°C and fed with Nannochloropsis sp. (7.5×104 cells/ml); the culture medium was replenished at 2-day intervals. Commercial foods for planktonic organisms were also tested. Four days after hatching, the metatrocophore stage is reached. It is characterised by a longer shape and the presence of two chaetigers. Nine days after hatching the larvae had reached the herpochaeta stage still having two chaetigers but with a noticeable swelling of the jaws; after 3 weeks the settling stage of the post-larva had been reached, with three chaetigers and a complete feeding apparatus. The settled post-larvae start to feed on both plant and animal detritus added to the culture vessels.