(1. Gasterosteus, Cuv). * Sides more or less protected by transverse scaly plates.
Three dorsal spines.
G. aculeatus, Linn. Syst. Nat. torn. i. p. 489. Bloch, Ichth. pl. 53. f. 3. Don. Brit. Fish. vol. i. pl. 11. Flem. Brit. An. p. 219. G. trachurus, leiurus, & semiarmatus, Cuv. et Val. Poiss. torn. iv. p. 352. pl. 98, & p. 361. G. trachurus, & gymnurus, Cuv. Reg. An. torn. ii. p. 170. Stickleback, Will. Hist. Pise. p. 341. tab. X. 14. f. 1. Bowd. Brit. fr. wat. Fish. Draw. 20. Three-spined Stickleback, Penn. Brit. Zool. vol. iii. p. 261. pl. 50. no. 129. Id. (Edit. 1812). vol. iii. p. 353. pl. 61.
From two to two and a half, rarely three inches.
(Form). Oval; rather elongated; sides compressed; tail slender; dorsal and ventral • lines equally convex: greatest depth about the middle, rather more than one-fifth of the entire length; head one-fourth; thickness a little more than half the depth: eyes large: cranium more or less striated, the striae formed of minute granulations: mouth protractile; when closed, the lower jaw advancing a little beyond the upper: both jaws with fine small teeth, but none on the tongue, vomer, or palatines: opercle large and triangular, the posterior margin rounded: no true scales, but the sides protected by a series of oblong osseous plates, varying in number, disposed in transverse bands; a similar plate, ascending from the base of the ventrals, reposes on the third and fourth of the above series; there is also another placed longitudinally on each side of the breast, and a large triangular one on the belly, having its base in a line with the ventrals, and its apex directed towards the vent; all these scaly plates more or less granulated in lines: instead of a first dorsal three free strong spines, a little distant from each other, more or less serrated at their edges, varying in length, but the second always longest; first spine above the first or second of the lateral scaly plates; second above the fourth; the third, which is much smaller than the other two, in a line with the apex of the triangular plate on the belly: soft dorsal commencing immediately behind this last spine; all the rays, except the first, branched: anal about half the length of the soft dorsal, with one short, curved, free spine immediately before the first ray: caudal rounded: ventrals consisting of one strong serrated spine, united by a delicate membrane to one slender soft ray scarcely one-third of its own length:
D. 3 - 10 to 13; A. 1/8 to 10; C. 12; P. 10; V. 1/1: sides of the tail sometimes furnished with a horizontal expansion of the skin forming a keel. Number of vertebrae thirty-three. (Colours).
* Hist rise. p. 327.
Back and sides olivaceous, sometimes passing into yellowish brown or dusky blue: throat and breast, in some individuals, bright fiery red: belly and Hanks silvery, with a pearly lustre.
Var.α . G. trachurus, Cuv. Yarr. in Mag. of Nat. Hist. vol. in. p. 522. fig. 127. a. Rough-tailed Stickleback, Yarr. Brit. Fish. vol. i. p. 76. The scaly plates extending the whole length of the sides; in number about thirty.
Var.ß . G. semiarmatus, Cuv. Yarr. in Mag. of Nat. Hist. vol. iii. p. 522. fig. 127. b. Half-armed Stickleback, Yarr. Brit. Fish. vol. i. p. 80. Lateral plates extending to a vertical line joining the vent and commencement of the soft dorsal; in number from twelve to fifteen.
Var.γ. G. leiurus, Cuv. Yarr. in Mag. of Nat. Hist. vol. Ill, p. 522. fig. 127. c. Smooth-tailed Stickleback, Yarr. Brit. Fish. vol. i. p. 81. Lateral plates from four to six; extending only as far as the pectoral fins, when these last are laid back.
Var. δ. G. brachycentrus, Cuv.? Short-spined Stickleback, Yarr. Brit. Fish. vol. i. p. 82. Lateral plates not extending beyond the pectorals: dorsal and ventral spines very short.
Common throughout the country in rivers and streams, as well as in stagnant waters. Is also found occasionally in the sea. Of active and lively habits. Is very voracious, and preys on worms and aquatic insects. Spawns, according to Bloch, in April and June; according to Cuvier, in July and August.
The above species is subject to great variation, not only in the number of the lateral plates, but in several other less obvious respects. The former may occasionally be found of every intermediate number between that which characterizes the G. leiurus, Cuv. and that which appears in the G. trachurus of the same author. This number, moreover, is sometimes found constant in specimens which differ remarkably in other respects; at other times, varying, when all other characters remain the same. From these circumstances combined, I feel satisfied that the above are mere varieties, notwithstanding the high authorities on which they stand recorded as distinct species. Perhaps it may be useful to state the result of a close comparison of a large number of individuals with each other from different localities.
Yarrell, Esq. These agreed in having the eyes very large; the space between rugose, with granulations disposed in lines; the teeth rather prominent; the osseous disk between the opercle and pectoral large; the lateral plates varying in number, but well-defined and very regularly disposed; the ventral plate narrow, more than twice as long as broad at the base; the dorsal and ventral spines long, the latter equalling two-thirds of the depth of the body, nearly straight, and often with serrated edges; sides of the tail generally, but not always, carinated.
Depth greater in proportion to the length than in no. 1; eyes much smaller; the rugose lines between as before; teeth similar; osseous disk behind the opercle much smaller; lateral plates few in number but well-defined; ventral plate very large, its breadth at the base contained only once and a half in its length; spines, the ventral especially, nearly as long as in the above, equally serrated, but not so straight, being slightly curved from their base; sides of the tail perfectly smooth.
Eyes intermediate in size between those of nos. 1 & 2, but varying slightly in different individuals; rugose lines on the vertex generally indistinct, sometimes wholly wanting with the exception of two, one above each eye, which are always present; teeth varying a little, but generally smaller than in either of the above; osseous plate behind the opercle generally larger than in the last, but seldom so large as in the Thames specimens; lateral plates varying in number, sometimes extending the whole length of the sides, but generally few, and irregularly disposed; ventral plate about twice as long as broad at the base; spines varying a little, but always much shorter (the dorsal especially) than in no. 1; ventrals equalling half the depth; sides of the tail, except in one or two instances, not carinated.
Of very large size, measuring full three inches. Eyes large, but less than in the Thames specimens; the space between smooth, with the exception of two deeply impressed lines, one above each eye; teeth moderate; osseous disk between the opercle and pectoral rather large; lateral plates five in number, and regularly disposed; ventral plate twice as long as broad at the base, its apex very obtuse; dorsal and ventral spines strong, but much shorter in proportion than in any of the former specimens, a little curved, their margins finely serrated; sides of the tail smooth, without any trace of a keel.
From the above details it will be seen how each character varies in its turn, and at the same time how little connection there is between the variation of one part and that of the others *.