Some measurements and counts on a fresh-water fish, Aplocheilus latipes (T. & S.)(with text-figs. 1-4)

Abstract

Dealing with 236 wild specimens of black coloured Aplocheilus latipes (T. & S.) caught at Kurihama, Kanagawa Prefecture, some biometrical observations have been carried out in regard to body-length (standard length), body-weight, length of fins, number of circuli found on the scales taken from the median area below the dorsal fin, weight-length relationship, relative-growth of fins to the body-length, relevance between number of the circuli and body-length, and that between the number of the circuli and the age of the fish. The specimens dealt with comprise 108 males, 15-31mm in body-length, and 128 females, 15-34mm long, and may be referable into 2 age-groups (I and II) on basis of the number of the circuli. The group-I appears to be made up of fish of 1 year-old measuring less than 26mm and 28mm in body-length in male and female respectively, and the other group appears to be of the animal of 2 years-old measuring more than the lengths given above. The mode of the body-length of the group-I is 21-22mm in male and 24-25mm in female, and that of the group-II is 24 26mm and 28-29mm respectively (Fig. 1).The weight-length relationship of the fish (Fig. 2) may be represented by the following formulae: W=.0.00002597L^2.933 in male, W, =0.00001212L^3.183 in female respectively. Wherein W is body-weight (g) and L is body-length (mm). The relevances between body-length L) and the lengths of the pectoral (F₁), dorsal (F₂), anal (F₃) and caudal (F₄) fins are linear in trend (Fig. 3). These are expressed by the equations given below: . F₁=0.27L+4.26, F₂=0.291A-4.51, F₃=0.27L+4.44, F₄=0.25L+4.97 in male, and F₁=0.24L+4.43, F₂=0.16L+3.18, F₃=0.13L+3.05, F₄=0.21L+4.29 in female. Regarding to lengths of the pectoral and anal fins of both the groups, I and II, and that of the dorsal fin of the group-II, sexual difference is found to exist. Female pectoral fin is longer than male one, on the contrary, female anal and caudal ones are shorter than those of male. The difference of the anal fin is salient as enough as to use the fin for sex recognition at least in regard to the fish measuring more than 15mm in body-length.
The number of the circuli is given in the Fig. 4 in relation to the body-length. As seen in the figure the number successively increase until the fish attain a length of about 23mm in male and about 24mrn in female, and becomes constant and again it turns to increase at 26mm and 28mm long in male and female respectively. As listed in the Table 4, the scales of the males, 20-26mm long, have 1 5.2-18.2 circuli on average' and those of the females, 20-28mm in body-length, have 13.0-17.8 circuli on average. On the other hand, the scales of the males, 26-32mm long, are provided with 19.0--23.5 circuli, and those of the females 28-34mm long, are developed with 19.3-23.1 circuli on average. And the scales taken from the 7 A. latipes measuring 21.5-30.0mm in total length (about 16-24mm in standard length), reared by HIYAMA during 5 months from June 14 to November 14, 1938, in outdoor aquarium are furnished with 12.1-16.0 circuri on average. Judging from such facts given above, it seems that the fish measuring more than 26mm long in male and 28mm long in female belong to the group of 2 years-old. Finally it may be mentined that the circuli show a tendency to be more variable and larger in number in males than in females.