Kuthekfubd. — On Salrnonidae. 243 



river-bed, so the fertility of the soil through which a river flows 

 (altitude, climate, exposure, and the temperature of the water 

 being also taken into consideration) determines the abund- 

 ance and quality of the vegetation on land and under the 

 water, and the supply of insect life, Crustaceans, &c, which 

 form the staple food of the trout. As a rule cold snow-fed 

 rivers contain much less food than those draining warmer 

 lower levels, and the fish in them are later in getting into 

 condition. 



It must be borne in mind that each river has a limited 

 permanent carrying-capacity, and will only do justice to a 

 certain stock of fish. If overstocked the result must inevi- 

 tably be deterioration ; hence it may be expected that in time 

 our non-migratory Salmonidce will deteriorate in size, and 

 that we must look to annual visitors from the ocean (which, 

 owing to the configuration of these Islands, is never far away) 

 to keep up the record this colony holds for growing big trout, 

 largely established at first by the fact that the virgin waters 

 in which they were liberated contained abnormal quantities 

 of food. 



III. Indigenous Fish. 



Before proceeding to discuss subjects surrounding the in- 

 troduction of Salmonidce into New Zealand, it may be inter- 

 esting to take a cursory glance at some of the indigenous fish 

 inhabiting our rivers. The only true representative of the 

 SalmonidcB is the beautiful little Retropinna, or smelt, two 

 varieties of which at least are found in our rivers and lakes. 

 Somewhat allied to this fish, the graceful upokororo (Proto- 

 troctes oxyrhynchus) , or native grayling, about whose life- 

 history and habits so little is known, is found in many of our 

 streams. The upokororo used to be plentiful in our rivers, but 

 of late years have been thinned out by the formidable trout 

 we have introduced, by mining operations, and, no doubt, by 

 clearing the bank vegetation for farming purposes. It is said 

 to be an almost unique variety, very like the Haplochiton, 

 which inhabits the cold, fresh waters of Tierra del Fuego, 

 and is allied to a fish found in Australia, the Yarra herring. 

 Though said to differ from a true Salmonoid in certain struc- 

 tures, it is, I believe, a representative of the family in this 

 hemisphere. I have never heard of their being taken in salt 

 water, but they certainly have a habit of disappearing and 

 reappearing again in a ghostly fashion, which makes one wish 

 for a further acquaintance with their migrations and spawn- 

 ing habits. I would suggest that the Westland Acclimatisa- 

 tion Society, who have their hatchery in a suitable place, be 

 -asked to keep some in their ponds for the purpose of studying 

 their life-history. 



