106 A NATURALIST IN TASMANIA ch. 



threatened to overwhelm the whole community, 

 and so served to draw its different parts to- 

 gether for mutual defence and in a common 

 interest. 



The distinction between north and south does 

 not only concern the soil and other economic 

 features ; it is also noticeable to the naturalist 

 in the distribution of the river fish, certain species 

 being confined to the rivers which flow out on 

 the north into Bass's Straits, and being entirely 

 absent from the rivers running in a southerly 

 direction. Since the introduction of the English 

 Trout these native fish are becoming rarer and 

 rarer every year, and the time is probably not 

 far distant when they will be in danger of extinc- 

 tion. The freshwater fish characteristic of the 

 northern rivers are three in number. The Fresh- 

 water or Cucumber Herring (Prototroctes maraena) 

 (Fig. 28) belongs to the family Haplochitonidae, 

 which is confined in its distribution to temperate 

 South America, Victoria, Tasmania, and New 

 Zealand. This fish, which is rather closely related 

 to the Salmonidae, used to afford the most admir- 

 able fishing, as it rises to a fiy and shows fight, 

 and is excellent to eat, but it is now extremely 

 rare, being only caught in any quantities in the 

 rather inaccessible rivers of the north-west coast. 

 It is silvery in colour, rather similar in shape to 

 a Salmon Trout, and often scales several pounds. 

 The breeding habits of the fish are not clearly 

 understood, but it seems certain that they descend 



