Rhodichthys regina, found in 1,280 fathoms of water, is uniformly bright red in colour.
A. Agassiz says in his reports on the dredging operations on the west coast of America: ‘The coloration of the deep-sea fishes is comparatively monotonous. The tints are all a light violet base, tending more or less to brownish or brownish yellow, or even to a greenish tint, especially among the Macruridæ. Some of the Liparidæ were of a dark violet, and one species was characterised by a brilliant blue band. The Ophidiidæ, Nemichthys, and the like, are usually of an ashy violet tint, while in Ipnops and Bathypterois the tints were of a decidedly yellowish brown.’
That the deep-sea fish are usually devoid of any pronounced spots, stripes, and other markings, is now well recognised. It may not be altogether out of place, however, to refer briefly to a few exceptions.
The black circles on the abdomen of Neoscopelus macrolepidotus have already been referred to.
Halosaurus johnsonianus, has a black spot on the tail.
Aulostoma longipes has three pairs of large black spots on the ventral side, but the specimen taken in 1,163 metres of water by the ‘Talisman’ was probably a young one.
It is very probable that in all the exceptional cases, when fish taken in deep-sea water have exhibited such spots and markings, they are examples either of fish that have quite recently adopted an abysmal habitat or of young specimens exhibiting ancestral inherited characters.
In referring to a specimen of Raja circularis, taken by the ‘Triton’ in 516 fathoms, Günther says: ‘It is notable that the spot on each side of the back which in littoral specimens is variegated with yellow is much smaller in the deep-sea specimen and uniformly black without yellow.’
It seems to be then a very general rule among fishes that as they migrate into deeper water the spots and stripes, so conspicuous among many forms living on the surface and in shallow water, disappear, and the coloration of the body becomes more evenly distributed and uniform.
Among the Mollusca, the deep-sea Cephalopods seem to be usually violet, but an Opisthoteuthis Agassizii caught by the ‘Blake’ is stated to be of a dark chocolate colour, a Nectoteuthis Pourtalesii reddish-brown, and a Mastigoteuthis orange brown, while of the specimens brought home by the ‘Challenger,’ Cirroteuthis magna was said to be ‘rose’ when captured, and the spirit specimens of Cirroteuthis pacifica and Bathyteuthis abyssicola were purplish madder and purplish brown respectively.