STICKLEBACKS. 
reckoning the vertebrce in a specimen of the G. leiurus and in one of the 
Irish sticklebacks of a similar length, I find that the number in the latter 
exceeds that in the former species, and that they are throughout more 
regularly equidistant than in the G. leiurus. 
In the three English sticklebacks, G. trachurus, G. semiarmatus, and 
G. leiurus , the bony plate covering the head is much stronger than in the 
Irish fish — the outline of the lower jaw more angular — the lips smaller 
and less fleshy — the number of rays in the fins different, consisting gener- 
ally, in the Irish specimens, of twelve in the dorsal, ten in the pectoral, 
eight in the anal, and twelve in the caudal. In the three English Gas- 
terostei, also, the ventral spine is longer, but not so broad as in the Irish 
fish — the dorsal spines considerably longer, and the plates whence they 
spring proportionately larger. The following is the measurement of the 
spines in the four species : — 
G. trachurus 
Total length of fish. 
. 2 in. Ulin. 
First dorsal spine. 
2\ lin. 
Second. 
2f lin. 
Ventral. 
4 lin. 
G. semiarmatus 
2 6 
2* 
3 
41 
G. leiurus 
. 2 6 
2§ 
3 
4 
Irish species, . 
G. brachycentrus . 
' | 3 0 
li 
If 
31 
1 2 
In the last species * the membrane extends to the extremities of all the 
spines. 
About Belfast I have taken the smooth-sided sticklebacks — G. leiurus 
and G. brachycentrus — from ditches in the low grounds, from clear 
mountain-streams at an elevation of 600 feet above the level of the sea, 
from the muddy rivers Blackwater and Lagan, and from water which was 
partially salt (here G. leiurus only), when, contrary to what might be ex- 
pected, the largest were invariably found where the temperature was 
lowest, specimens there ( G . brachycentrus ) not uncommonly attaining the 
length of three inches, and perfectly free from the pearl-like tumours, 
which, ^adhering to the body, infest those inhabiting the comparatively 
warm waters of the lower grounds. This short-spined stickleback here 
exhibits, in all respects, the same colours as the most common of the 
English varieties ; of many of the larger individuals captured in the 
month of September, about the one-half were red on the under parts. In 
large shoals, too, I have remarked fully this proportion to have assumed 
the scarlet, and in the early summer months I have observed that full- 
grown fishes, in which the most intense shade of this colour prevailed, 
never appear to be with spawn,! very few in that state being so much as 
faintly tinged with it. This Gasterosteus and the trout ( Salmo Fario ) 
seem not to co-exist in some of our smaller rivers, or do so very partially. 
In the stream whence the largest of these were taken, trout ( Salmo Fario ) 
were a dozen years ago very common, and the stickleback unknown, and 
it is only since the almost total disappearance of the trout that this fish 
has been established in its waters. In a similar stream, issuing from the 
same mountain-range, at about four miles distance, the trout yet main- 
* Agreeably to the view taken in the Hist, des Poiss., the term “species” 
was here applied to G. brachycentrus. I was disposed at the time (1834) to re- 
gard it as a local variety, but had not the means, which have since been afforded 
by a comparison of specimens from numerous localities, to arrive at a certain 
conclusion on the subject. 
f So late as the 19th Sept., 1832, I remarked one large with spawn. 
