Marine Department View Of Oyster Parasites

Press, Volume CII, Issue 30155, 12 June 1963, Page 11

Marine Department View Of Oyster Parasites

(New Zealand Press Association)

WELLINGTON, June 11

While predators and parasites did probably play some part in limiting the number of Foveaux Strait oysters, it was most unlikely that they were the main cause of the present low catches, said the Secretary of Marine (Mr G. L. O’Halloran) today.

Mr O’Halloran was commenting on a suggestion by Dr. F. B. Slack, senior lecturer in applied fisheries at Victoria University of Wellington, that these predators and parasites could wipe out the oyster beds.

Although the number of Bueh pests fluctuated, the “five finger" brittlestar, described by Dr. Stack as an enemy of oysters, had always been abundant on the grounds. There was no evidence that the only parasites so far identified in the oysters had recently increased in number and there was no proof that the “five finger” was the host of the parasite, Mr O’Halloran said.

“Both have been studied by the Marine Department biologist on oysters, Mr D. Stead, and the investigation of their habits is being intensified now the initial survey on the location of the beds has been largely completed.” said Mr O'Ha'lloran. Some confusion apparently existed between the “five finger” brittlefish and the starfish, which was a serious enemy of oysters in Europe and North America. They were entirely different species.

The starfish with thick powerful arms, was able to prey on adult oysters by forcibly dragging the shell open and engulfing the oyster within. Where it was common it did considerable damage to oyster beds. It was, however, quite scarce in Foveaux Strait and could have little effect on oyster beds there. Mr O’Halloran said the brittlestar had long thin arms, was incapable of opening an oyster shell and appeared to feed on small shellfish and other organisms which it swallowed whole.

“Investigation has shown it does eat some oysters, up to about half an inch, but these form only a small portion of its food. Several dozen brought up with commercial catches of oysters were examined jointly by Mr Stead and Dr. Slack on an oyster boat, but not one contained any oysters.” Although, on present evidence it did not seem that expensive measures for the destruction of the “five finger” would be justified, oystermen would help if they destroyed the brittlestars

taken in their catches, said Mr O'Halloran.

This could be done by putting them in boiling water or taking them ashore. They should not be broken or cut into pieces and thrown back because some of the pieces would grow back into complete brittlestars, thus increasing its numbers. “The parasite found in the oyster is being studied by Mr Stead and by Dr. Miller, of the Milliport marine station, Scotland,’’ Mr O'Halloran said.

“In the oyster it occurs as a microscopic animal and it almost certainly has another worm-like stage in some kind of fish not yet discovered. “There had been many instances of attempts to intro-

duce oysters from one country to another resulting in the introduction of organisms that wrought havoc in established fisheries. Britain and the United States had learned these lessons the costly way and now took precautions against repetition.”

He said the Marine Department was aware of the presence of parasites in the oysters before Dr. Miller’s letter was published and the fact had already been mentioned in the press. The parasite could be a factor responsible for periodic high mortality of oysters but there was no real evidence to support this. Mr O’Halloran said those fond of oysters should not be deterred by academic statements.

The parasites which invaded the oysters were not harmful to human beings, many millions of oysters having been consumed over the years without ill-effect. Commenting on Dr. Slack’s statement that many dead oysters were found, Mr O’Halloran said Mr Stead had for some time known and had reported an apparent increase in the number of shells from recen<tly-dead oysters on the east beds where he had gone with Dr. Slack.

Contrary to what had appeared in Dr. Slack’s comments no dying oysters were found in the catch.