FISHES PHENOMENAL AND ECONOMICAL. 



Since the date of the earliest successful consignment of salmon ova to 

 Tasmania, by the ship "Norfolk" in the year 1864, literally millions of salmon ova 

 have been similarly imported, their fry being hatched out at the Salmon Ponds, near 

 New Norfolk, and . subsequently liberated in the Derwent and other apparently 

 suitable rivers. Sometimes these young salmon were turned loose into the rivers in 

 the earlier or parr form, and at other times in the silvery " smolt " condition when 

 they were ready to make their first migration to salt water. In no instances, 

 however, have these salmon smolts been authentically known to return to the rivers 

 the following year as " grilse " or in subsequent years as full grown salmon. Some 

 have suggested that the young salmon on arriving at the sea were invariably devoured 

 by sharks, barracouta, or other predatory fish. In that case, however, the salmon- 

 trout that descended as smolts with them at the same time would have shared their 

 fate. That, however, by no means happened, numbers returning to the rivers. It 

 may be added that the active young salmon were far better qualified to take care of 

 themselves in the salt water than many of the species of fish indigenous to Tasmania. 



It occurred to the writer that possibly the question of temperature was an 

 essential element in the refusal of the salmon to adapt themselves to their new 

 environments, and a series of thermometrical observations was inaugurated. From these 

 experiments it was ascertained that the sea water on the Tasmanian coast averaged 

 some ten degrees higher than that of the British seas, and corresponded more nearly 

 with that of the Mediterranean on the South Coast of France. 



This fact was in itself a sufficient explanation of the disappointing results so 

 repeatedly obtained. The salmon, unlike its hardier relation the trout, is known to 

 be particularly sensitive to any changes of external conditions, and more especially 

 to those of temperature. Consequently, the millions of young salmon fry and smolts 

 that have been liberated in the rivers of Tasmania and made their way to the ocean, 

 finding the temperature of the sea water in the vicinity of Tasmania too warm for 

 their comfort, have, it may be predicted, wandered away, presumably in the direction 

 of the Antarctic Ocean, in search of colder water. Interesting evidence in support 

 of the correctness of this interpretation is afforded by the fact that precisely similar 

 results have attended the attempts to establish salmon in rivers of the South of 

 France which debouch upon the correspondingly warm waters of the Mediterranean. 

 The young salmon have thriven as fry, parr, and smolts in the French rivers, but, 

 on migrating to the sea, they wandered away and did not return to their native 

 streams to spawn, as they would have done under their normal conditions. 



