A STUDY OF THE VARIOUS ASPECTS OF THE BIOLOGY OF THE GREEN MUSSEL MYTILUS VIRIDIS LINNAEUS OF IMPORTANCE TO ITS CULTIVATION IN SINGAPORE/JOHORE WATERS

Abstract

The various aspects of the biology of the green mussel Mytilus viridis Linnaeus were investigated with a view to cultivating it. The study was mainly confined to the Eastern Johore Straits and covered the period 1969 to 1972. The characteristics of the environment at four stations in the Johore Straits and one in the Singapore Straits were studied and compared. The hydrology of the Western Johore Straits was investigated for the first time. The results showed no significant seasonal differences between the environmental conditions in the Eastern and Western Johore Straits. The distribution of the mussel in the Johore and Singapore Straits was studied. The factors affecting the distribution are discussed. Induced spawning techniques on ripe mussels were tried. The methods used are discussed. The seasonal pattern of spawning, the size at first maturity and the fecundity of the mussel were determined. Spawning occurs throughout the year, but is more abundant in the period April/May to October/November. The complete life cycle of the mussel from fertilised egg t o metamorphosis was observed. The spat settlement levels and seasonal variations in settlement density were observed. The results show that settling follows shortly after spawning; coconut coir ropes serve as excellent spat collectors and that the mussel has no effective competitor for settling sites. The crawling behaviour of M. viridis was investigated and its significance is discussed. The seasonal variations of stomach contents of the mussel and its food preferences were studied. Diatoms, tintinnide and detritus were readily ingested, but dinoflagellates were less readily taken in. The implication of this finding in relation to mussel culture is discussed. The shell length-width-depth relationship and the shell length-total weight, shell length -flesh weight and shell length-shell weight relationships were determined. The value of these relationships to the main purpose of this report is pointed out. The growth of M. viridis (under caged conditions) at various localities in the Johore and in the Singapore Straits was observed and compared. It was found that growth is rapid in the Johore Straits and slow in the Singapore Straits. The factors affecting the growth were investigated and are discussed. The growth of naturally-occurring mussels was observed up to a period of seven months, while that of caged mussels was followed till one year from settlement at Station 1 (Kelong No. E10) in the Johore Straits. The results clearly show that M. viridis can reach a market size of 5-7 cm (shell length) in 4-6 months from settlement. The sex ratio and the asymptotic length of the mussel were determined. The factors affecting the changes in population density with size are discussed. The production of M. viridis in the Johore Straits was determined on an experimental scale. The results of these experiments and that of the other aspects of the biology of M. viridis indicate the feasibility of cultivating the mussel in these waters. The problems of pollution and parasites in relation to mussel culture are pointed out.