244 Transactions. — Zoology. 



The strictly fresh- water varieties of fish (such as carp) are 

 intolerant of salt water, and on examination of the indigenous 

 fresh-water varieties in this colony it will, I think, be found 

 that they are all more or less tolerant of salt water, and prob- 

 ably, almost without exception, descended from marine an- 

 cestry at no very remote period in the world's history. Many 

 of them, such as the smelt, eels, and inanga, at times frequent 

 salt and brackish water ; while some of our marine fishes, 

 such as the flounder, grey mullet, and kahawai, run up into 

 fresh water, the two former living and thriving in some waters 

 in the North Island where they cannot obtain constant and 

 permanent access to the sea. 



IV. Salmonid^e in General. 



In his opening chapter on Salmonida, Dr. Giinther remarks 

 that there is no other group of fishes which offers so many 

 difficulties with regard to the distinction of the species, as 

 well as certain points in their life-history, as this family. 

 Their almost infinite variety is dependent on age, sexual de- 

 velopment, food, the ever-varying properties of water, and the 

 tendency to interbreed exhibited by many of the so-called 

 varieties. Colouration seldom assists us in distinguishing the 

 species, varying as it does with the haunts of the fish and the 

 seasons of the year. It is imitative, the colour of the fish 

 rapidly adapting itself to its surroundings. A living trout of 

 dark colour placed in a white basin full of water becomes pale 

 in half an hour, and in some days almost white. Conversely, 

 a trout of light colour placed in a black vessel rapidly assumes 

 the colour of the bottom. Hence, in almost every river the 

 varieties of trout have local peculiarities of colour, which are 

 favourable as a protection to the fish against its natural ene- 

 mies. As a rule, clear rapid rivers produce trout with intense 

 ocellated spots. In large lakes with pebbly bottoms the 

 same fish are bright and silvery, with x-shaped black spots. 

 In pools and parts of lakes with a muddy or peaty bottom 

 they are of a darker colour generally, smudged and blotchy in 

 their marking ; and, when enclosed in caves and dark holes 

 w r ith but little light, often jet-black or nearly so. The action 

 of brackish or salt water soon gives them a bright or silvery 

 coat, as a rule sparsely spotted, none of the spots being ocel- 

 lated. 



Size depends chiefly on the amount of suitable food avail- 

 able, and the colour of the flesh on the particular nature of 

 the food, the pink or red colour being probably produced by 

 the red pigment of many salt- and fresh-water Crustaceans on 

 which they greedily feed. 



This group of fish may be divided into many varieties, in- 

 cluding the Salmones proper, such as the species of salmon. 



