96 INTRODirCTION AND BREEDING OF FISH. 



doubt, are confined by tlie laws of their organization to a warmer 

 temperature than that of the Mediterranean, but among them 

 there must be many whose habitat is of a wider range, many 

 whose powers of accommodation would enable them to acclimate 

 themselves in a colder sea. 



We may suppose the less numerous aquatic fauna and flora of 

 the Mediterranean to be equally capable of climatic adaptation, 

 and hence there will be a partial interchange of the organic popu- 

 lation not already common to both seas. Destructive species, thus 

 newly introduced, may diminish the numbers of their proper prey 

 in either basin, and, on the other hand, the increased supply of 

 appropriate food may greatly multiply the abundance of others, 

 and at the same time add important contributions to the aliment 

 of man in the countries bordering on the Mediterranean.* 



Some accidental attraction not unfrequently induces fish to fol- 

 low a vessel for days in succession, and they may thus be enticed 

 into zones very distant from their native habitat. Several years 

 ago, I was told at Constantinople, upon good authority, that a 

 couple of fish, of a species wholly unknown to the natives, had 

 just been taken in the Bosphorus. They were alleged to have fol- 

 lowed an English ship from the Thames, and to have been fre- 

 quently observed by the crew during the passage ; but I was un- 

 able to learn their specific character.f 



Many fish which pass the greater part of the year in salt water, 

 spawn in fresh ; and some fresh-water species, the common brook- 

 trout of New England for instance, which under ordinary circum- 

 stances never visits the sea, will, if transferred to brooks empty- 



* The dissolution of the salts in the bed of the Bitter Lakes impregnated the 

 water admitted from the Red Sea so highly that for some time fish were not 

 seen in that basin. The flow of the current through the canal has now re- 

 duced the proportion of saline matter to five per cent., and late travellers 

 speak of fish as abundant in its waters. Interesting observations on the pro- 

 cess of interchange between the two seas, which seems to be a slow one, will 

 be found in Petermann's Mitthelungen, No. III., for 18 — , p. 120. 



f Fifteen or twenty years ago, the Italian Government imported from France 

 a dredging machine for use in the harbor of La Spezia. The dredge brought, 

 attached to its hull, a shell-fish not known in Italian waters. The moUusk, 

 finding the local circumstances favorable, established itself in this new habitat, 

 multiplied rapidly, and is now found almost everywhere on the west coasf 

 of the Peninsula. 



