12 



discussion, enjoys an almost cosmopolitan distribution. Its habitat, as described in Dr. Johnson's 



catalogue of non-parasitical worms in the year 1S65, is as follows : — " Found living between seams of slaty 

 rock near low-wator mark, and burrowing in the fine soft mud which lines the fissures." By a well- 

 known Queensland oyster cultivator, I have been informed that the same species of worm was noticed 

 by him many years ago burrowing in the mud-filled crevices of timber work in Sydney Harbour. The 

 species, like most members of its class, is an essential mud lover, and its natural instincts guide it in its 

 earliest larval condition to seek out and establish itself within any appropriate mud-lined crevice. 



So extensive have been the depredations of this mud disease with its associated worms in New 

 South Wales, that many of the formerly most productive oyster grounds of that Colony have been 

 practically depleted, and it is owing to this disease, mainly, that instead of exporting, that Colony is now 

 so largely depenclont on Queensland and New Zealand for its supplies. Much anxiety is naturally 

 manifested to exclude this destructive agency from taking up its abode in Queensland waters, and having 

 that circumst;inco in view, the fullest information concerning its probable cause and possible prevention 

 will doubtless prove acceptable. In this direction [ herewith reproduce the views on this subject 

 expressed in a lecture upon " Oysters and Oyster Culture in Australia," I contributed to the meeting 

 of the Australian Association for the Advancement of Science held at Christchurch, New Zealand, in 

 January last. After enumerating the more salient features of the disease as already described, I thus 

 continue : — 



" The rock oyster, Osfrea (jlomerata, affected by the disease is, as previously remarked, a species 

 that attains to its maximum development in brackish water, and indeed survives exposure to fresh water 

 immersions in times of floods that would prove fatal to the so-called mud oyster, Ostrea edidis. As a 

 corollary to these b.-ai^kish water proclivities of Ostrea ijlomerata, its most luxurious development in New 

 South Wales has been high up the riverine estuaries that so abundantly intersect the coast line. The 

 Hunter, the Hawkesbury, and the Clarence rivers may be mentioned, not only as the most important of 

 the oyster-growing areas, btit aJso as those in which the worm disease, or, as it in-iy be more correctly 

 termed, the 'mud disease,' has been most prevalent. In my opinion it is the alteied conditions of these 

 rivers, brought about mainly through human agency, that has induced the diseased condition of the 

 oysters, their waters, in fact, being rendered more or less incapable of supporting the mollusc in a healthy 

 state. 



"Through the clearance of the land and the establishment of townships and settlements through- 

 out the watersheds of these rivers, the rainfall which in former days fell upon and was more completely 

 absorbed by the primeval forests is now carried quickly away, and emptied by drains and culverts into 

 the watercourses communicating with the rivers. Simultaneously with this augmented discharge of 

 water into the rivers a vastly larger quantity of sediment is brought down, accompanied by a considerable 

 percentage of organic and chemical pollution that had no place in the composition of the water under 

 those conditions in which the oysters originally grew and flourished. This greatly augmented accession 

 of flood water, with its accompaniment of sediment and chemical pollution, cannot exert other than a 

 very deleterious influence upon the riverine oyster fisheries. 



" A case in point in which the oysters, formerly growing abundantly many miles up a river's course, 

 have been gradually pushed further and further down towards the sea through the agencies just described 

 fell under my personal observation in Tasmania. In the river Tamar, debouching on the northern coast- 

 line of that colony, the mud oyster, Osfrea edulis, was originally abundant from the Heads half- way to the 

 town of Launeeston, some forty miles distant. By degrees, as borne testimony to by residents of the 

 district, the oysters have gradually disappeared from the formerly prolific higher portions of that river 

 known as Whirlpool Reach and the Middle and Eastern Arms. Ou my first visit to the Tamar estuary a 

 few oysters were still left in the lowest bay known as the West Arm, but these, both young and old, were 

 in a dead or dying state, owing chiefly to prolonged immersion in water containing an insuSicient amount 

 of saline ingredients, but organic pollution from the town of Launeeston probably also playing an im- 

 portant part in their destruction. Within a few years after this first visit oysters were practically extinct 

 in the Western Arm, and no success attended tlie eff'orts made to resuscitate the fishery in that district 

 by artificial culture. The last lingering remnant gathered there were in a decidedly unhealthy state, the 

 shells being discoloured and wanting in solidity, and the contained oysters being in the poorest possible 

 condition. 



" Should the interpretation here suggested be correct with relation to the diseased condition of the 

 New South Wales Oyster Fisheries, it is evident that the prospects are but small of recovering the ground 

 lost to oyster culture in the several districts aftected. It will consequently be incumbent on the oyster 

 growers of that colony to make the most of the water area left to them where the water is pure and not 

 liable to be invaded by the disease, and, if they are ambitious to regain that position formerly held in 

 which the colony was independent of supplies from external sources, they will require to turn their 

 attention to the culture of the mollusc on a far more scientific basis than has been hitherto attempted in 

 New South Wales waters." 



Respecting the existing or prospective invasion of the Queensland oyster-beds by this mud disease, 

 with its accompanying parasitic worms, I am pleased to be in a position to report that there is, at all events, 

 no evidence to hand of its presence at the present time. A little while since there was some suspicion of 

 its having made its appearance in Wide Bay, and a few specimens of oysters which, on being opened, were 

 found to contain a parasitic worm, were submitted for my examination. The worm, however, in these 

 solitary instances, was a nereid representing a different genus than that associated with the New South 

 Wales disease, and had apparently gained access to the shell through a perforation originally made by a 

 boring whelk. There are circumstances, in my opinion, which will operate for a long while, and. it is to be 

 trusted, permanently, against the introduction of the disease under notices into Queensland waters. In 

 New South Wales, as previously stated, the oyster fisheries devastated belong entirely to riverine systems 

 that have become much altered in character, and polluted by sedimentary deposits through the clearance 

 of their inland watersheds. The oyster grounds of Moreton and Wide Bays, on the other hand, have 

 such near and free communication with the open ocean that they are not influenced to anything approach- 

 ing the same extent by floods from the tributary rivers, and from the effects of which they speedily 

 recover. It 



