DOUBLY-SPOTTED GOBY. 
255 
that in this case the adaptation takes place in a much 
more intricate manner, but is always guided by the 
simple or variegated colours of the surroundings. It 
is often very hard to discover one of these fishes, when 
at rest among the water-plants. 
“During autumn and winter the colours of the 
Doubly-Spotted Goby are duller, and the sexual distinc- 
tion in this respect less marked. Furthermore, different 
individuals seem to possess the power of changing co- 
lour in different degrees. One fish takes twice as long 
as another, before it acquires a uniform dark or light 
colour; one retains a colour fairly (though never com- 
pletely) unchanged for a long time, while another, 
though on the same bottom and under the same cir- 
cumstances, seems to undergo an incessant shifting of 
colour. If we continue the above experiments for a 
lengthy period of time upon the same tish, the chro- 
matophores become distinctly fainter.” 
Most of the colour characters given in the above 
description are, however, not entirely peculiar to the 
Doubly- Spotted Goby. The selliform spots, in particular, 
have been described as characteristic of the next two 
species, especially of Gohius pictus, and also occur, as 
Lilljeborg lias already remarked, in Gohius minutus, 
even though some difference may be shown in their 
prominence and position. The black caudal spot is also 
common to the following species, though in them it 
seems never to be so sharply defined; and though the 
emerald spots on the sides, sometimes sharply separated 
by a black space between them, have not been observed 
in the following species, they still have a corresponding 
marking of black, simple or bisected spots, which some- 
times appear like transverse bands. As is shown in 
v. Wright’s figure, there also occur in Gohius flavescens 
two black spots, starting from the eyes down the cheeks 
and snout, the one ending just behind the corner of 
the mouth, and the other running almost straight for- 
ward. We may hence judge how inconstant are the 
characters derived from colour; but the black spot, 
during life with an azure lustre, that occurs at the end 
of the dorsal fin in the two following species, and which 
Heincke has given as one of the external sexual char- 
acters of the male of Gohius minutus , is apparently 
wanting in Gohius flavescens. 
The habits of the Doubly-Spotted Goby are no less 
interesting than its beauty of colour. It is one of the 
most handsome aquarium fishes and pleasing enough, 
though its propensity of hiding itself renders it difficult 
to discover in aquaria which are thickly overgrown 
with plants. It sustains life without difficulty in fresh 
water, if gradually accustomed to it; but if suddenly 
removed from salt water to cold fresh water, it be- 
comes rigid and dies with expanded fins, just as when 
it is thrown into strong spirit immediately after its 
capture. Lowe states of this species, according to Day, 
that it readily learnt to take food from his hand. “Its 
movements,” says Heincke, “are restless and active; and 
with the funnel-shaped ventral fins it can firmly attach 
itself even to the perpendicular walls of the aquarium.” 
In its free state the Doubly-Spotted Goby prefers 
a rocky bottom, thickly overgrown with seaweed, at a 
depth of from 1 to 10 fathoms; but it is also found 
in weedy spots, where the bottom consists of stones or 
gravel. The Royal Museum possesses several specimens 
which were taken in a dredge at spots of this nature. 
Malm, however, as well as Parnell, found it living in 
quite another manner, more resembling the life of the 
Sticklebacks. “In contradistinction to all the Gobies,” 
writes Malm, “which in Sweden keep to water so shallow 
that they may be observed without difficulty, it is only 
very seldom that this fish is seen near, or, more strictly 
speaking, at the bottom. I have observed this on only 
few occasions, and it has then been a solitary, full- 
grown male that has swum in and rested on a rock; 
but, on leaving its resting-place, has risen in the water, 
not creeping, as it were, along the bottom like Gohius 
niger , mice ops, pictus and minutus. As a rule it is 
only seen in larger or smaller, close-packed companies, 
in mid- water, so to speak, and especially at clear spots 
in the Zostera region. The water may be two or three 
fathoms deep or more, but the shoal stays, sometimes 
almost still, a foot or two below the surface. I have 
often seen shoals containing several hundred small spe- 
cimens and only one or two full-grown individuals, 
thus seeming to be composed of a family or two that 
led an isolated life in this manner. When disturbed, 
the shoal sinks deeper in the 'water, but as a rule, 
soon rises again. I have never succeeded in enticing 
this fish to take a bait, though I have taken its kin- 
dred species in this manner; but when it leaves the 
bottom, at least in the daytime, it may easily be taken 
with a hand-net.” 
The spawning-season occurs in summer, from 
May to August. The female attaches the eggs to the 
shells of dead shellfish or Balanids, and the male keeps 
faithful and courageous guard over them. 
