330 



ICHTHYOLOGY. 



Geographi- jgpth^ would be necessary. Wliile the Scomberoids and 



*^b ?■""'" other fishes that habitually swim near the surface would be 



, , _ f more directly influenced by temperature, both as regulating 



"' v'*' the supplies of food, and as acting immediately on their 



own constitutions. 



There can be no doubt that species have been framed 

 to endure certain degrees of temperature only ; that some 

 which thrive in water, just above the point of congelation, 

 would perish in the tepid ponds of intertropical regions, 

 and vice versa. l)r Davy has shown that a continued heat 

 of 80° will addle the egg, and destroy the embryo of the 

 common Salmon ; the fact of that species being limited to 

 the countries lying northwards of the 41st parallel of lati- 

 tude being most probably dependent on the small power 

 the species has of resisting heat. On the other hand, the 

 experiments of Broussonnet show that by using much cau- 

 tion, and elevating the temperature gradually, fish of tem- 

 perate regions may be brought to endure a heat of 97° 

 Fahr. The Arnbassis. thermaUs is reported in the Hts- 

 toire des Poisso?is, on the authority of M. Renaud, as ca- 

 pable of inhabiting the hot springs of Cannea, near Trin- 

 comalee, in a temperature of 115''-25 Fahr. ; but there is 

 reason to suspect some inaccuracy of observation here. 

 Dr Davy visited these springs in 1817, when of seven 

 wells, then existing, the hottest and principal one, and the 

 one which he thought supplied the others, had a tempera- 

 ture of 10o*75° Fahr. ; but the heat was said to vary, and 

 he was told that it occasionally rose to 110°. The coolest 

 of the seven wells had a heat only of 86° Fahr. ; and in one 

 only, whose temperature was 91°, did he see any fishes. 

 Many small fishes, such as the Anteiumrii, and others of 

 the less active swimmers, dwell in the floating islands of 

 Sargasso, and most probably spawn among its stems. 

 Though they find shelter in its mimic groves from the 

 predacious birds and fishes, yet they must be exposed to a 

 pretty high temperature under the direct rays of a tropical 

 sun, against which, however, nature has furnished them 

 with a protection, in the copious secretion of mucus which 

 envelops their skins. The Anabas, again, ascends the palm 

 trees of Bengal, and endures the heat of an atmosphere 

 rising to 97° in the shade ; while the Callichthys of tropi- 

 cal America must be exposed to at least an equal heat in 

 its overland journevs. Fish constituted to brave such heats 

 would speedily perish, there is every reason to believe, in 

 colder regions ; and a review of the whole class leads irre- 

 sistibly to the conclusion that many species have been cre- 

 ated solely to meet the conditions of existence which cer- 

 tain limited localities afford, such as the Ambli/npsis of the 

 Mammoth Cave of Kentucky, and the Siluroids of the mud 

 volcanoes of the Andes. 



The creation of a single pair ot each species in certain 

 spots, and the diffusion of their progeny from thence, has 

 been of late a favourite subject of speculation ; but this 

 implies the subsequent calling into existence of the more 

 predacious kinds, when the others had multiplied, so as to 

 need a check ; and the simpler supposition, and the one that 

 is most consistent with the facts that are knowni, is that 

 when the ocean was ;n a condition to support ichthyic life 

 it was peopled by the Great Creator, each species being 

 placed in svifficient numbers in the district best suited to 

 its structure and habits, and the purpose it was designed 

 to serve, while at the same time the balance between re- 

 production and supplies of food was provided for by a suf- 

 ficient number of the rapacious kinds. And, moreover, that 

 new species were created when a change in the condition 

 of the ocean and its boundaries led to the extinction of the 

 older races, and rendered such an exercise of creative 

 power necessary. 



Our limits will not permit us to stray into further specu- 

 lation, and we shall conclude this article by hastily glancing 

 at a few general facts. The northern seas, which are for 



butioQ. 



the most part comparatively shallow, nourish many of the Geographi- 

 Sderogenidce, which feed at the bottom and frequent shelv- cal Distri- 

 ing, sandy shores or sandbanks. The majority of these 

 have barbels or portions of the pectoral fins detached or 

 otherwise organized as fingers or organs of touch. An al- 

 lied group, the Uranoscopidce or Triuhiiiida, have often the 

 tips of the anal rays similarly constituted. The Gadida, 

 also, which have barbels under the chin, are ground feeders ; 

 and these, with the Cotti and Scorpanae among the Sclero- 

 genids, and the fi'esh-water Trultte, and anadromous Sal- 

 mones, are the most characteristic groups of fishes in the 

 northern seas. The same generic forms of sea-fish, but 

 not the same species, reappear in corresponding southern 

 latitudes ; the Cotti, Scorpcence, and Gadidte being also 

 conspicuous among the South Australian fishes. The 

 Sclerogenids are not unknown in the middle tropical dis- 

 tricts of the ocean, but they are different generically ; the 

 Cotti and ScorptEna being replaced by Pelors, St/nanceia, 

 and others of a different aspect. There is a general resem- 

 blance between the fishes of the northern and southern 

 extra-troj)ical seas, so that emigrants to Australia have 

 very generally bestowed familiar European names on 

 the sea-fish they found in the country of their adoption. 

 In like manner there is a similarity of general aspect, 

 but an almost total difference of species between the fish 

 of Behring's Sea and the Sea of Ochotsk, and those of the 

 German Ocean — though there are some facts which lead 

 us to infer that in a higher parallel still there is a zone 

 in which the same species form a circumpolar ichthyic 

 fauna. This is different, both generically and specifically, 

 fi-om the fragments of the antarctic circumpolar groups of 

 fish, which have reached us through Sir James Ross, the 

 only navigator who has made collections in the high 

 southern latitudes. Some genera, of few species, are the 

 more remarkable from their occurrence both in the northern 

 and southern seas, though in form of distinct yet closely 

 resembling species. Macrourus has two representatives in 

 the seas of Greenland and Norway ; two in the Mediter- 

 ranean ; and two in the Australian seas. Lophius has one 

 species in the European seas and another in the sea of 

 China, so much alike that very close comparison is required 

 to distinguish them. Zeus, also, and the allied genus of 

 Capros, have each a species in the Mediterranean and tem- 

 perate parts of the North Atlantic, as well as in the seas of 

 Australia. The Greenland and Iceland Nntacantlms, also, 

 or Campilodon of Fabricius, reappears in the seas of South 

 Australia with exactly the same generic aspect, but some 

 subordinate difference of details, showing the species to be 

 distinct, and without having been detected in the interven- 

 ing districts of the ocean. No example of the genus, M. 

 Valenciennes remarks, has ever reached the Paris Museum 

 from the Indian Ocean. The true SalmonidcBor Tritttreof 

 some authors are confined, as we have already more than 

 once remarked, to the northern hemisphere. They do not 

 pass the great Himalayan range. We have seen none from 

 Afi-ica, nor a figure of any species among the drawings 

 made at Canton of all the fish brought to that market, 

 though the Salmonida are both various and plentiful in 

 the Kamtschadale seas. The C/uiraciiiidrr, once inclu- 

 ded in the Salmon family, because they possess the charac- 

 teristic Linnacan mark, an adipose fin, are chiefly South 

 American ; while the Scope/inidcr, another family having 

 also an adipose fin, are oceanic, being found in all seas from 

 the German Ocean to the Chinese, Australian, and Poly- 

 nesian waters, the only large district from which specimens 

 have not hitherto been brought being the North Pacific 

 and Behring's Sea. They are small fish, mostly nocturnal 

 in their habits, and though many of them carry phosphor- 

 escent lamps, they have until lately escaped the observation 

 of mariners ; but when the practice of keeping a trawl 

 overboard becomes more frequent, it is likely that they 



