OCR Text |
Show 1870.] INTRODUCTION OF SALMON INTO TASMANIA. 751 of the ova of Salmo trutta, which arrived in April 1866. These ova were kept in a separate hatching-box, and hatched in May following. Part of the fry were placed in the same pond with the Salmon-fry hatched that year ; the residue were placed in a separate pond and rill constructed for them. In October 1867, more than half of the fry in the Salmon-pond assumed the smolt dress and went to sea, the gratings being purposely removed. In October 1868, all that were left of the fry in the Salmon-pond put on the smolt scales and left for sea. Of the fry placed in the other pond, a number assumed the smolt dress in October 1867, but were purposely kept back, in the hope that spawn might be obtained without the usual migration seawards. The smolts became very restless ; several threw themselves on to the banks and were destroyed ; others died, and amongst them one which I preserved and have forwarded by this mail for preservation to the Society. In October 1868, all the fishes that were left in the separate pond, and which had not become smolts the year before, put on the bright scales and exhibited the usual restlessness. Again several died, and before the commencement of winter, in M ay 1869, the Commissioners lowered the water to make certain alterations in the pond, and found the fishes reduced in number to twelve, all of which were handsome silvery fishes, without the slighest trace of parr markings, and varying in weight from nearly half a pound to more than a pound. During June and July 1869, five spawing rids were constructed by these fishes in the rill attached to their pond. The old fishes were then shut off from the rill by a fine wire grating, to prevent their interfering with the ova, which commenced hatching in September. In December 1869, 500 of the fry from these ova were set at liberty in the River Huron, the remainder being retained to increase the breeding stock, and to ascertain whether the migratory instinct would recur in these fish. The fry so retained are now, at eight months old, the picture of health, and exhibit the brilliant orange fin from which the trivial English name of the parr of Salmo trutta is derived. One of these parr I have also forwarded for preservation to the Society. From the foregoing details it is manifest that, if the specimen sent to England was hatched from ova received in April 1866, that fish must have left our pond as a smolt in October 1868, and remained a year, either in the river or in the sea, without adding one inch to its length, or one ounce to its weight, while its brethren, unnaturally detained in fresh water, not only increased in size, but arrived at sexual maturity and deposited healthy ova. From Dr. Giinther's letter it is clear that, if he had received the fish sent from a Scotch instead of a Tasmanian river, he would have pronounced it a healthy fish, as it might then have been a smolt of either 15 months or 27 months old without presenting any abnormal conditions; and is it not quite possible that a few pairs of the smolts which went to sea in October 1867 may have returned to the river (as many British authorities hold they do) in the February following as breeding fish, which would deposit ova in June or July |