FISH. 



477 



has access to the smaller streams inhabited by trout, 

 knows that if a trout under tlic bank be tickled, it 

 will press against the hand as if very much pleased 

 with the operation ; and that. if tickled sufficiently it 

 may be lifted out of the water without offering any 

 resistance. 



The mucous tissue is understood to be the seat of 

 colour in all animals ; and in the fishes it is remark- 

 able for its brilliant tints and iridiscent reflection?, 

 the finest of which in general fade, when the fish is 

 dead, and this tissue becomes dry and rigid. The 

 epidermis is very soft in fishes, and very generally 

 covered with a mucous secretion. It extends to the 

 scares as well as to those parts that have none, and it 

 also moistens the shells of aquatic molluscain the living 

 stale. In fishes it appears to be seasonal, as it often 

 comes off in patches of considerable size, when there 

 is no reason to think that the fish is unhealthy. 



The scales of fishes are placed on the epidermis, 

 or rather they consist of thin tissues of epidermis 

 with layers of phosphate of lime between, and it is to 

 this structure that they owe their fine pearly lustre. 

 Generally speaking they are imbricated, or placed 

 over each other like the tiles on a roof, with their 

 posterior margins free and generally rounded, and 

 often with a fringed margin. When they are ex- 

 amined by means of a powerful magnifier, they show 

 a very beautiful ramification of stria 1 , or little threads. 

 When the fishes are in fine condition, and especially 

 toward the season of reproduction, there is a beauti- 

 ful bloom and metallic lustre on the scales, in the 

 same manner as there is on the feathers of many 

 birds ; but when the season of reproduction is over, 

 and the fish are exhausted, as they always are upon 

 these occasions, the bloom goes off, and the surface 

 is dull and lustreless. The fish are unwholesome 

 when this is the case, and the rich and pearly lustre 

 of the scales is one of the surest signs of the fish being 

 in season, equally sure as the bright red of the gills 

 is that it has not been too long kept. This is remark- 

 ably the case with salmon, the pearly hue of which is 

 very lich when they first enter the estuaries of the 

 livers, but it wears off; and when they have spawned 

 they arc vernacularly termed " black fish," in which 

 state the capture of them is prohibited, though poach- 

 ers'do sometimes take them, then and sell tnem at no 

 small hazard to the lives or at all events the health 

 of the purchasers. 



In many species there are osseous plates, or tuber- 

 cles, or spines, instead of scales ; and where these 

 occur they have always more the consistency of hard 

 bone than the internal skeleton of the animals ; nor 

 is it unworthy of remark, that these bony appendages 

 to the skin are, generally speaking, more general 

 among the cartilaginous fishes, than among those that 

 have harder skeletons. The sturgeons have the sur- 

 face of the body studded with osseous plates resem- 

 bling limpet shells ; the sharks have it granulated with 

 tubercles; and many of the rays have it beset with 

 very hard and sharp hooked spines resembling teeth ; 

 and all these are cartilaginous fishes, with little or no 

 hard matter in their internal bones. 



It is farther worthy of remark, that this tendency 

 to accumulate the salts of lime in the form of scales 

 plates, tubercles, and should accompanies the 

 formation of gelatine, which, though found in ver} 

 small quantity or not at all in the bones, exists in vast 

 quantity in the skin; so much so that our best glue 

 and finest jelly are obtained from the membranes o' 



ish. Nor is there any doubt that if the trimmings 

 of the fins of fish, which are thrown away in such 

 quantities, were collected and prepared by the removal 

 of the fatty matter (which is chiefly dame or oil fat, 

 and might also be turned to valuable account) and 

 he other foreign substances, a great quantity of an 

 article very wholesome and nutrition? as food, and 

 very useful in many of the arts, might be recovered 

 at little cost from absolute waste. 



The protecting substances which we have now 

 mentioned, do not appear to be in any case intended as 

 direct defences against enemies ; but they, the scales 

 specially, answer some very important purposes in 

 the action of the fishes ; and it is worthy of remark, 

 hat those fishes which have not imbricated scales 

 with their margins free, are either more long and 

 lexible, or their fins more expanded, so that they are 

 ess active in swimming than those which have 

 Veer edged scales. The size of the individual scales 

 does not appear to be a matter of much importance, 

 so that the edges are free, because upon an equal 

 extent of surface small scales are probably as 

 advantageous as large ones. 



The action of the edges of the scales is this : 

 when the fish bends thp body strongly to one side in 

 the act of swimming, the iorce of the stroke would 

 throw the head in the other direction, and a certain 

 portion of the effort would be expended in actually 

 driving the fish back ; and this counteracting portion 

 would always be the greater fraction of the whole, 

 the more powerful the stroke, or, which is the same 

 thing, the greater the flexure of the body. But 

 when the fish is covered with scales, the posterior 

 edges of which are free, any flexure or stroke of the 

 tail toward one side must cause a proportional rising 

 of the edges of the scales on the other, and the edges 

 thus raised must each lay hold of the water, and not 

 only prevent motion back wards, but give considerable 

 effect to the stroke. 



But besides these which we have mentioned, 

 there are other spinous appendages to the 

 coverings of fish which are of a more formidable 

 character, and which may be regarded in the light 

 either of offensive or defensive weapons. These 

 have rather the form of spines, very sharp at the 

 points, by means of which punctured wounds can be 

 given, and they are often finely granulated over their 

 surfaces, so that while they penetrate they lacerate 

 like a file, and the wound is of a cankering and fes- 

 tering character ; so much so that there is a belief that 

 some of these species are poisonous, as is alleged of 

 the spine of the dorsal fin in the dragon werver, 

 Trcu /linos draco. That poison should be secreted on 

 a spine in the fin of a fish, subjected to constant 

 washing in the sea, and without the least vestige of 

 a poisoning apparatus, which is always very complete 

 and apparent in those animals which are known to 

 inflict poison, would be rather singular ; and though 

 it is the general belief among those who receive 

 wounds from these fish, there does not appear to be 

 any more truth in it than there was in the old story 

 of the deer poisoning those that were wounded by 

 his antlers. It seems to be nothing more than a 

 ragged wound which is inflicted in those cases, and 

 we know that such a wound given by a steel instru- 

 ment will often produce the most serious consequences. 

 These spines are placed in different parts of the 

 body in different fishes. In the fins on the sides of 

 the tail, on those of the head, on the gill lid, on the 



