CHAPTER XVIII. 



THE FISHES OF THE BRACKISH WATER. 



On such parts of a coast at which there is a mixture of fresh 

 and salt water, either in consequeuce of some river empty- 

 ing its water into the sea or from an accumulation of land 

 surface water forming lagunes, which are in uninterrupted or 

 temporary communication with the sea, there flourishes a 

 peculiar brackish water fauna which is characterised by the 

 presence of fishes found sometimes in sea-, sometimes in 

 pure fresh-water. 



This fauna can be rather sharply defined if a limited 

 district only is taken into consideration ; thus, the species of 

 the brackish water fauna of Great Britain, the Pacific coast 

 of Central America, of the larger East India Islands, etc., can 

 be enumerated without much hesitation. But difficulties 

 arise when we attempt to generalise in the enumeration of 

 the forms referable to the brackish water fauna ; because the 

 genera and families enumerated include certain species and 

 genera which have habituated themselves exclusively either 

 to a freshwater or marine existence ; and, besides, because 

 a species of fish may be at one locality an inhabitant of 

 brackish water, at another of the sea, and at a third of fresli 

 water. The circumstance that these fishes can live in sea 

 and fresh water has enabled them to spread readily over the 

 globe, a few only being limited to particular regions ; there- 

 fore, for the purposes of dividing the earth's surface into natural 

 zoological regions the brackish water forms are useless. The 

 following fishes may be referred to this Fauna : — 



