|Feeding and digestion in bivalve larvae|
Lucas, A. (1990). Feeding and digestion in bivalve larvae, in: Morton, B. (Ed.) The Bivalvia: Proceedings of a Memorial Symposium in honour of Sir Charles Maurice Yonge (1899-1986) at the 9th International Malacological Congress, 1986, Edinburgh, Scotland, UK. pp. 177-193
In: Morton, B. (Ed.) (1990). The Bivalvia: Proceedings of a Memorial Symposium in honour of Sir Charles Maurice Yonge (1899-1986) at the 9th International Malacological Congress, 1986, Edinburgh, Scotland, UK. Hong Kong University Press: Hong Kong. ISBN 962-209-273-X. 355 pp., more
During the larval life, three nutritional stages can be distinguished: endotrophy (or lecithotrophy), mixotrophy (or intermediate trophic stage) and exotrophy (or planktotrophy). In Mytilus edulis, for example, reared at 17-20°C, the first stage lasts 2 days, the second about 6 days and the third about 20 days. This model is valid for most oviparous species of bivalves belonging to the planktotrophic group. Many authors assume that dissolved organic matter can be absorbed from sea water at any time during the larval life. But a net gain in weight resulting from flux and influx of amino-acids has not been clearly demonstrated. In a longterm experiment on Mytilus edulis larvae, a circadian rhythm of release and absorption of ten amino acids was observed. This suggests that short-term experiments cannot resolve this problem. For particulate matter, no clear information is available on inert particles. Three types of living particles can be distinguished: nannoplankton, picoplankton and bacteria. The first is well known and represents the only food supplied in hatcheries. The second, which has a high productivity, can be ingested by larvae, but has previously been ignored. The same applies for bacteria: using clearance techniques and the grinding of larvae, bacterial ingestion has been shown to be a constant phenomenon and, by TEM observations, the presence of lysed bacteria in the digestive tract, including the crystalline style, has been demonstrated for Vibrio, Pseudomonas and some Gram + strains. In addition to clearance rate and radioisotope methods, observations by epifluorescence microscopy gave data on phytoplankton ingestion and digestion: quantity ingested, time of digestion, rhythm of feeding, selection of algae. Information gathered by this method allowed comparison of larvae living in experimental conditions (continuous feeding, large quantities of food, but poor variety) and in the wild (discontinuous feeding, limited food, but high variety). Enzymatic analysis has shown for Pecten maximus. hatchery larvae, an activity which was high for amylase and laminarinase, when the larvae were fed and lower when the larvae were unfed, whereas the activity of a lisozyme-like enzyme, which could break bacterial membranes, appeared to be high in both fed and unfed larvae.