Euthebfurd. — On Salmonidte. 247 



species ; but it is probable that they do not make such 

 lengthened journeys at sea as the salmon proper are sup- 

 posed to do, but frequent the shallower water on the 

 coast. 



Even within the limits of a single species (so-called) no 

 two are found to be exactly similar, but there is a tendency to 

 diverge from the original type in such direction as to preserve 

 and increase useful varieties — a law of variability by adapta- 

 tion, which is destined to modify every organism so as to fit it 

 for new conditions of existence. A notable instance of this 

 occurs in the gillaroo trout of Ireland, which have developed 

 gwasz'-gizzards to enable them to crush and digest the small 

 fresh-water snails and shells found in certain lakes. It will 

 be interesting to watch whether similar developments are 

 found in any of the varieties in our lakes at the antipodes. 



In short, my theory is that, whatever variety we liberate 

 of the ordinary species of trout, it will develope into a Salmo 

 novie-zealandice, suited to the water in which it is liberated, 

 and corresponding with trout in similar latitudes in the 

 Northern Hemisphere more closely than with the varieties 

 found in the more northern latitudes of our Mother-country. 

 I do not think that these fish will retain the characteristics of 

 the variety found in the environment from which they were 

 taken, and consider that the results already obtained in New 

 Zealand have proved this. 



VII. Salmo irideus. 



Turning to a more subtle family, the Salmo irideus, or 

 rainbow trout, which we have successfully introduced into 

 several of our rivers in the colony, there is considerable con- 

 troversy as to what this variety really is. The progeny of ova 

 taken from the Salmo gardneri, or steel-head, of British Colum- 

 bia, are apparently identical with the progeny of the rainbow 

 trout, and it is commonly believed by some of the experts that 

 they are the same fish, and that the rainbow trout when it 

 takes to sea-going habits developes into the steel-head. It 

 will be very interesting to see whether this proves to be the 

 case in New Zealand. 



Personally, I am inclined to think that this species, in 

 common with the rest of the trout on the Pacific Slope, is more 

 allied to the char family than the trout. Its spawning habits 

 are not like those of the trout, and in its play when hooked 

 it is like a salmon. It lacks many of the shy habits of the 

 trout, and is certainly the best sporting fish we have yet intro- 

 duced. I do not think there is any probability of this variety 

 crossing with the brown trout in our rivers, and I doubt their 

 thriving well together. 



There seems to be a marked divergence in species between 



