5^ 



8a.lmon trout, and the rcniahiilor salmon ; and tliat tlic 300 

 salmon trout had been liberated in 18G7, while 3,000 of the 

 salmon had been liberated in 18G5, and the remainder with 

 the salmon trout in 1867. I now propose to deal seriatim 

 with Dr. Giinther's reasons for concluding that the second 

 grilse is a salmon trout, and first the " short broad tail, with 

 a perfectly truncated caudal fin." Though Dr. Giinther, in 

 the catalogue, gives, as one test, " the form of the caudal 

 fin in specimens of a given size, age, and sexual condition," 

 there is no statement which implies that this is an infallible 

 test in immature fish, and as an actual matter of fact, the 

 caudal fin of the first grilse is decidedly emarginate or 

 forked, which was one argument used by me for deciding that 

 it was a true salmon, because salmon trout of even less size 

 almost invariably have this fin truncated, or even rounded. 

 (See Proceedings Royal Society, Tasmania, 1874, p 15). 

 Again, it is remarkable that every salmonoid (except the 

 second grilse) caught in the Derweut estuary last year, and 

 of which four had reached the size at which the caudal fins 

 of salmon trout usually become truncated had the caudal fin 

 more or less distinctly forked. Two of those fish are now 

 before you, and speak for themselves, especially when com- 

 pared with the male smolt sent to the salmon commissioners 

 from England, and in which the caudal fin is but slightly 

 more forked than in its larger companions. In spite of this 

 discrepancy I wish it to be distinctly understood that I 

 regard the second grilse as identical in species with all these 

 salmonoids, and am disposed to place little reliance on this 

 test where the fish are approaching the adult stage. 



An enormous diversity will be found in the form of the 

 caudal fin in specimens of salmo fario or common trout, many 

 of which have it truncate when the fish are but 5 or 6 inches 

 in length, while others show emargination when 17 or 18 

 inches long. 



There appears to be, as hinted by Dr. Giinther, some 

 subtle connection between the state of sexual development 

 and the form of the caudal fin, and as we know that a per- 

 centage of the male salmon parr at only 6 inches in length 

 do arrive at actual sexual maturity, and are capable of 

 impregnating the ova of the full grown female salmon, is it 

 not quite possible that these rapidly developed male fish may 

 exhibit the truncate fin at an earlier stage than their sexually 

 immature brethren ? 



The second reason assigned is " 14 scales in a transverse 

 line between the adipose fin and lateral line." Here again a 

 marvellous discrepancy exists amongst the salmonoids taken 

 in the estuary of the Derwent, for out of some 30 specimens 



