CIV DISEASES AND CAUSES OP DESTECCTION. 



Line-fishing * in the sea, as employed for the capture bf commercial 

 fish, may be divided into two kinds, hand-lining and long-lining, while 

 angling does not call for any remarks. It may be observed that fish are 

 very insensible to pain (vol. i, p. 5). 



■ DISEASES AND CAUSES OF DESTRUCTION. 



The diseases and causes of the destruction of fish may bp divided into 

 (1), those due to the condition of the water in which they reside; (2), 

 atmospheric disturbances and accidental causes ; (3) diseases by which they 

 are afi'ected, including those of the ova and of infancy ; (4) misplaced energy 

 in fishermen and poachers; (5), injuries occasioned by the lower animals. 



1. Waters may be virulently and directly poisonous, at once aSecting' 

 the Hfe of the contained fish and even that of cattle or man ; or else they 

 may be rendered mechanically unfit for fish to live in, as when the 

 presence of mud chokes their gills and prevents respiration. Or the water 

 may be indirectly affected owing to some deleterious agency having destroyed 

 the living food which was previously present, or occasioned disease in the 

 resident fish. When a river in India becomes unduly full of mud the crabs 

 retire to the banks, and even the eels leave the stream for the wet grass in 

 the vicinity. This attempt to. escape from water loaded with ingredients 

 inimical to life has likewise been observed' among the invertebrate forms of 

 Europe, as was some years since pointed out by M. Gerardin, in Prance. A 

 series of experiments and investigations showed that colour, taste, odour, or 

 chemical composition cannot invariably be accepted as criteria of whether 

 water is wholesome or the reverse, but that such must be looked for in its 

 effect upon the animals and plants which reside in it. When fish died from 

 river pollution, it was observed that molluscs sometimes saved themselves 

 by hiding under leaves and waiting there until the danger had passed away; 

 thus, in July, 1869, Limn^a remained five days out of the water. 



Among plants one of the most delicate was found to be the watercress, 

 and it was remarked that when some deleterious substance from a starch 

 factory obtained access to the Croult above the cress-beds of Gonesse, all 

 these plants died within a few hours ; the pollution removed, the cress-beds 

 again flourished. Pond weeds and veronicas only live in water of good 

 quality ; mints, rushes, and water-lilies, accommodate themselves to 

 mediocre water ; Oarex is still less sensitive ; and lastly, the most robust of 

 aquatic plants is a species of reed, the Arundo phragmites, which resists the 

 most infected water. Among molluscs, the Physa fontinalis lives only in 

 very pure water, the Valvata piscinalis in that which is healthy, while others 



* The reader is referred, for a full account o:^ the various modes and manners, to the " Sea 

 Fisherman," by J. Wilcbcks. 



