Rajaguru: Biology of Cynoglossus are! and C Itda from Indian waters 



331 



male and 254 female C. lida. (Refer to section on 

 Reproductive biology, for Stages I-VI.) 



The significance of variation in the estimate of b, 

 from the expected value B ( = 3) for an ideal fish was 

 tested by the i-test in both sexes of C. arel and C. lida 

 (James 1967): 



Sb 



where B = hypothetical b ( = 3), and Sb = standard error 

 of b. 



Analysis of covariance (Snedecor 1956) was used for 

 all comparisons. 



Reproductive biology 



Tonguefishes have no secondary sexual characters to 

 distinguish the sexes. In females with gonads in ad- 

 vanced stages of maturity, ovaries can be seen easily 

 through the body wall when the fish is held against 

 light. In earlier stages of maturity, sexes are distin- 

 guishable only after dissection. Extension of gonads 

 into body cavity, and their color, shape, and size, were 

 noted after dissection. Ovary length was measured to 

 the nearest mm, while weight of testis/ovary was 

 recorded to the nearest mg. Ovaries were fixed in 

 modified Gilson's fluid (Simpson 1951) for ova diameter 

 studies. 



To investigate the distribution pattern of ova in dif- 

 ferent regions of the ovary, ova were taken from an- 

 terior, middle, and posterior regions of eyed-side and 

 blind-side lobes of ovaries in different stages of matur- 

 ity (Clark 1934, Hickling and Rutenberg 1936, de Jong 

 1940). Ova diameter measurements in each part were 

 noted separately. Results showed a uniform distribu- 

 tion of ovum size in different parts of both ovarion 

 lobes. Hence to study development of ova, random 

 samples of '^^500 ova per ovary were measured from 

 ovaries representing Stages I-VI (a total of 108 

 ovaries, at 18 ovaries/stage in C. arel, and a total of 

 168 ovaries, at 28 ovaries/stage in C. lida), using an 

 ocular micrometer at a magnification which gave a 

 value of 12.5^ (0.0125mm) to each micrometer division 

 (m.d.). Ova diameter-frequency polygons were drawn 

 after grouping the ova into 3 m.d. (0.04 mm) class- 

 intervals. 



Spawning seasons in both species were determined 

 from percentage occurrence of different maturity 

 stages during various months of the year. 



Generally, gonad weight depends on size and stage 

 of gonadal development. To account for effects of dif- 

 ferential body size on gonad size, gonad weight was 

 expressed as a percentage of body weight (Nikolsky 

 1963). This ratio, 



Weight of gonad x 100 

 Weight of fish 



is termed gonadosomatic index (GSI). To determine 

 the spawning season, GSIs for various months were 

 calculated. 



Relative condition factor (Kn) was calculated for in- 

 dividual fish of both sexes from the formula (Le Cren 

 1951), 



Kn = W/W 



where, W_ = observed weight, and W = calculated 

 weight (W = a-i-bx). Monthly mean values of Kn 

 were also calculated to confirm the spawning season. 



To determine minimum length-at-first-maturity (i.e., 

 Lm or L5o = length at which 50% of fish are mature), 

 specimens of C. arel and C. lida were grouped into 

 15mm and 7mm class-intervals, respectively. Sexes 

 were treated separately. Percentage occurrence of im- 

 mature and mature fish of various length-groups was 

 determined, and then percentage occurrence of mature 

 fish was plotted for both sexes. 



Fecundity was determined by the gravimetric meth- 

 od. For this study, 26 ovaries of C. arel (from specimens 

 200-439mmTL) and 19 of C. lida (161-201 mm TL) 

 were used. Since some ova might already have been 

 shed, ovaries with oozing ova were not used. Ovaries 

 were removed, measured to the nearest mm, and 

 weighed to the nearest mg. From each ovary, three 

 subsamples (each ~50mg) were taken and weighed 

 after removing excess moisture, and fixed in modified 

 Gilson's fluid. From each of these subsamples, yolked 

 ova were separated and counted. Mean number of ova 

 from three subsamples was multiplied by the ratio of 

 subsample weight: ovary weight to obtain an estima- 

 tion of the total number of mature cva in the ovary. 

 Numbers of ova per mm body length, per g body 

 weight, per mm ovary length, and per mg ovary weight 

 were also calculated. Fecundity of C. arel and C. lida 

 was related to total length (TL), total weight (TW), 

 ovary length (OL), and ovary weight (OW) using linear 

 regression. Statistical comparisons (Snedecor 1956) of 

 fecundity to TL, TW, OL, and OW were made. 



To determine the differential distribution of sexes 

 during the spawning migration, as well as during ag- 

 gregation, the sex ratio was calculated for each month. 

 To test the homogeneity in distribution of males and 

 females, the chi-square formula was used. 



Classification of maturity stages 



Maturity stages were indexed for both sexes of C. arel 

 and C. lida, following the ICES scale (Lovern and 

 Wood 1937), with the following modifications. Color, 

 shape, and extension of the ovary into the body cavity. 



