X 
THE COLOURS OF FISHES 
223 
not be in addition some assisting optical effect. 
A similar but even more interesting case is that 
of the green pipe-fish ( Siphonostoma typhle ), often 
quoted as an instance of protective resemblance. 
In this form a similar combination of yellow and 
black pigment occurs, but there is some doubt 
whether the green colour is not in part due to the 
action of the reflecting tissue. This pipe - fish, 
though usually green, may appear in a brown form, 
while the common pipe-fish ( Syngnathus acus ) is 
always brown. The common pipe-fish also contains 
yellow and black pigments, but the yellow is said by 
the authors to be more orange-coloured than that 
of the preceding form. It is, however, curious to 
note that the three pigments, that of the mackerel 
(■Scomber scomber) and those of the two pipe-fishes, 
yield solutions whose spectroscopic characters are 
almost the same; this certainly suggests that the green 
is primarily a result rather of structure than of pig¬ 
ment. True green pigments in fishes were, however, 
described some time ago by Mr. G. Francis in certain 
of the Wrasses (species of Odax and Labrichthys ), 
but the observations have never been repeated. 
The Mediterranean members of the family are said 
by Krukenberg to owe their green and blue colours 
to structural effects. 
In general, we may say of the colours of fishes 
that they are either pigmental or structural, and that 
the only pigments which have been described with 
certainty are lipochromes or melanins. In most 
cases both kinds of pigments occur simultaneously, 
but in some, as in the gold-fish ( Carassius auratus), 
the melanin pigments are entirely absent. The 
