MATURATION AND SPAWNING OF THE MYSTAX IN THE NORTHERN ARABIAN SEA

S. M. SHAMSUL HODA Centre of Excellence in Marine Biology, University of Karachi, Karachi-32-

ABSTRACT Maturity studies carried out on Thryssa mystax (Bloch & Schneider), collected from commercial landings at Karachi Fish Harbour, from January to December, 1977, show that the female-male ratio is 1.26 : 1, and, as revealed by- ova-diameter polygons, S'pawnmg occurs twice a year. There are two peak spawning seasons, in January-March and June-July, as borne out by the close approximation of GSI and relative condition coefficient. The minimum size at sexual maturity was about 140 mm TL for both sexes. The relations between total length of fish and length and breadth of gonads, and between fish weight and gonad weight have been determined. The logarithmic relationships between fecundity and total length and body weight and ovary weight have also been eatablished.

INTRODUCTION make a significant contribution to the clupeiod landings on the Karachi coast throughout the year. Studies on their systematics and biology have been made in (Day 1889, Chidambaram and Venkataraman 1949, Devanesan and Chidambaram 1948, Palekar and Karandikar 1952, Venkata­ raman 1956, Dharmamba 1959, Masurekar and Rege 1960, Dutta 1961, Rao 1963, 1964, Whitehead 1967, 1972) and in Pakistan (Hoda 1976, 1979, NORAD/Pak Fisheries Programme 1978). Thryssa mystax (Bloch & Schneider) and T. dussumieri (Valenciennes) are among the common species of anchovies caught along the Pakistan coast in the northern Araibian Sea. The present report deals with the maturity and spawning of T. mystax.

MATERIALS ASID METHODS The 411 samples were collected at random from the commercial landings at Karachi Fish Harbour, West Wharf, Pakistan, from January to December 1977. Data on total length (TL), weight (acutaMy the mass), sex, mauration (Wood 1930) and goand length, breadth and weight (mass) were recorded. The ova were measured after Hickling and Ruteniberg (1936), De Jong (1940) and Clark (1945). Fecundity was determined by counting the ova in a portion of the known weight of the preserved ovary and calculating the total number of ova from the total weight of the ovary. Relative condition coefficient 214 HODA wa^ calculated after Le Cren (1951) and Blackburn (1960). To determine GSI (Gonosomatic index), gonad weight was recorded as percentage of the body weight, including gonad.

OBSERVATIONS Sex ratio' Sex ratio was 1.26 female : 1 male. The observed ratios were tested against an expected 1 : 1 ratio by the method of X^ (Chi-square). X^ values of high significance occurred in January, March, June, September and November (Table 1) with a preponderance of females. The data for all other months appear to satisfy the null hypothesis. Sex ratios varied with the length (Table2)- Signi­ ficant X^ values, with dominance of females, occurred at 160, 170 and 180 mm TL. Size and weight of gonad The log-log regression between fish weight 'X' and gonad weight 'Y' calculated by the method of least square, yielded the following relationships: Testis: Log Y = -3.0576 + 1.3727 Log X (r = 0.831, S.E. = 0.137 and 1.1035 to 1.6419 for 95% C.L.) Ovary: Log Y = 0.3319 + 0.7529 Log X (r = 0.625, S.E. = 0126 and 0.5065 to 0.9994 for 95% C.L.)

TABLE 1. Chi-square test for T. mystax in different months. (d.f. =1).

Months Male Female Proportion of male X2 January 6 23 &.21 9.966* February 42 27 0.61 3.261 March 40 71 0.36 8.658* April g 3 0.73 2.273 May 25 25 0.50 000 June 4 12 0.25 4.00 July 9 9 050 000 August 6 6 0.50 0000 September 3 16 0.16 8.895* October 12 11 0.52 0045 November 12 16 0.43 0572 December 15 10 0.60 1.00

Pooled 182 229 0.44 5.375* * Significant at 5% level. MATURATION AND SPAWNING OF ANCHOVY 215

TABLE 2. Chi-square test for T. mystax ast different size groups. (d.f. "= !)•

Size group Male Female Proportion (mm) of male X2

90 1 0.25 1.000 100 2 2 0.50 000 110 4 2 0.67 0.667 120 3 6 0.37 1.000 130 22 18 0.55 0.400 140 40 32 0.56 0.889 150 46 32 0.59 2.513 160 28 50 0.36 6.205* 170 21 42 0.33 7.000* 180 10 21 0.32 3.903* 190 5 10 0.33 1667 200 9 — 000 210 2 — 000

Pooled 182 229. 0.44 5.375*

* Significant at 5% level. . The 'F' values were significant (Table 3) indicating differences between the slopes of the regression lines for testes and ovaries. Therefore, two different re­ gression lines for males and females are adjusted for fish weight-gonad weight relationship. .„^.,, , A total of 115 males, measuring 90-190 mm TL, and 167. ..fehiales, measuring 90-205 mm TL, were grouped into twenty 5-mm.intervalsi and the mean values of the length and breadth of the testes and ovaries were calcui^ted

TABLE 3. Analysis of covariance for differences in the regression coefficients of the weight-gonad relaitionship. Deviation from regression Source of variation d.f. Reg. coeff. d.f. ; SS MS F-value Within ' ^ ~ • : ' Testis 44 , 1.3727 43 1.2502 0.2907 ';Ovary ••- 57 • tO.7529 56 2.5244 .*.«.0451 Pooled within d :, . . 99 , 3.7746 0.0381 Common 1001 0.9704 100 4.1564-1568 0.0416 10.0867 Difference between the slopes 1 0.3843 0.3843 (1. 99) 216 HODA for each group. In order to know how the sizes of the gonads are related to the length of the fish, the relationships between the length and breadth of the gonads and the total length of the fish were established by the method of least square (Table 4). It appears that the growth rates in the left lobes of the testes and ovaries are faster than in the right lobes of the testes and ovaries.

TABLE 4. The equations for the regression lines to show the relationships between fish length and gonadal length and breadth. (X = fish length, Y = gonadal length or breadth)

Equations 'r' S.E.of reg. coeff.

Total length-gonadal length Left lobe of testes: Y = -26.0414 + 0.3542 X 0.9642 0.0230 Right lobe of testes: Y = -28.2642 + 0.3360 X 0.9206 0.0336 Left lobe of ovary: Y = -25.8940 + 0-3427 X 0.9564 0.0247 Right lobe of ovary Y = -24.1126 + 0.2937 X 0.9716 0.0167 Total length-gonadal length Left lobe of testes: Y = -11.7669 + 0.1423 X 0.9059 0.0157 Right lobe of testes: Y = -10.2957 + 0.1149 X 0.9496 0.0089 Left lobe of ovary: Y = -6.8627 + 0.1026 X 0.9514 0.0079 Right lobe of ovary: Y = -3.1234 + 0.0477 X 0.9543 0.0035

Size at first maturity Fish in stage I were considered immature, those of II and III as matur­ ing and in stages IV-VI as mature. The specimens (229 females and 182

130 160 190 «0 liO 190 130 IM TOTAL LENGTH (mm)- FIG. 1. Size at first maturity of T. Mystax. A: female (Venkataraman 1956); B: feinale (pneKot study); C: male (present study). MATURATION AND SPAWNING OF ANCHOVY 217 -males) were studied for determining the size at first maturity. It is observed that 15% mature females and 21% matures males appeared first at 130-140 mm TL and that 47% females and 52% males at 140-150 mm TL (Fig. 1 B,C). The size at which 50% at the fish were found mature is 140-150 mm TL and in the present instance, this may be considered as the size at which first maturity is attained in both the sexes. About 90% maturity is attained at 160 mm TL. Fecundity For this study 23 specimens, 130-205 mm TL, of IV-VI stages of ma­ turity, were used. The equations of regression coefficients between total length, weight of the fish and weight of the ovary and number of ova are as below: Log F (fecundity) = -4.0785 + 3.6359 Log TL (r = 0.7586, SE. = 0.2564) Log F = 2.6259 + 0.8954 Log W (weight of fish) (r = 0.7801, S.E. ==0.1567) Log F = 2.5316 + 0.4450 Log W (weight of ovary) (r = 0.5092, S.E. = 0.1641) The significance of 'r' has been tested by the statistic 't' = r V n - 2/v'l - r^ (Snedecor and Cochran 1967) and it has been found significant at 5% level The 't' values obtained are 5.335 for fecundity-total length, 5.716 for fecundity- fish weight and 2.711 for fecundity-ovary wei^t relationships- (Figs 2 & 3), The

4.C 4.4 •• - / • / ^*-2 # * o / iL . w * O4.0

1 _/' • g3.e ' f'»

^ • ••'•••' J L_J_ 2-i 22 2.3 2X 1.2 1.4 1-6 LS 2.0 LOG TOTAL LEN6TH(mm) LOG WEIGHTlmg) FIG. 2. Relation between log length and log number of ova (left) and logwei^t and log number of ova (right) in T. Mystax. number erf eggs increases by 3.6359 of the totJd length. It is seen that the number of eggs produced varies consideraUy in fish of neariy the same body and ovary lengtii and weight. This may indicate that the eggs in this species are shed in batches. The fecundity ranged from 3580 to 24180, with a mean value of 10360 in fish of 130 to 205 mm TL and weight of 14 to 64 g. Ova diameter To determine the spawning time, a series of ova diameters were taken (Fig. 3). Ova diameters from ovaries of the same state of maturity were com- 218 HODA bined, averaged and pooled into 2-/^ m-division (m.d.) groups for plotting of frequencies (1 m.d. = 0026 mm). Ova less than 5 m.d. (0.13 mm) in diameter were eliminated. No difference was found to exist in the diameter grouping of ova from the different regions of the ovary in this fish. As the eggs mature and are ready to be shed, a fresh batch of immature e^s from the general stock starts maturing (Fig. 3). Thus, two modes in maturation indicate that two suc­ cessive batches are spawned.

20 VI ^'nOvt,

20 V \\J\.. a

20 a IV

1 I I ri -I I I I I I I I I I IJ M 2'S 3^ 3-3 3l> ^' U U) LOO OVARY WEISHTdngl ', MieROMET^R DIVISIONS dm d.00257«» FIG. 3. Relation between log ovaify weight and log number of ova (left) and frequency polygons of ova - diameters from ovaries of'- 14 mature-fish of TL 130-202 mm (Tight) in T, Myslax- ' • -• ,.>•••;. .Afy; <,^ . GSI (.Gowsomatic Index) - GSI values indicate the stage of maturity and were determined for each stage (Table 5). GSI values were al^, cal

TABLE 5. GSI values* for different stages of maturity in males and females Stage Male Female I 0.1183±n.0816 0.3636 ±0.2507 II 1.0631 ±0.6438 0.4977 ±0.1933 HI 2.3113 + 0.6065 3.0161 ±0.7263 IV 5.2522+1.0645 3.5392 ±0.6299 V 5.9084 ±1.0214 4.5875 ±0.6432 VI 5.9860 ±1.3546 5.6887 ±0.9348 VII 0.3615 ±0.1502 0.9573 ±0.9135

X ± S.E. t0.05(n-l )

6 6

S 5

i 1 * f

~ 3 • .1 1 m1 •1 «) 1 lAl <» 2 i" '/V

1 1

J F M A M J J A S 0 N 0 too 120 MlO 160 tM 3M MONTHS TOTAk, beuOTM Imml FIG. 4. Mean values of GSI in different months (left) and at different lengths (right) in T. Mystax.

I.OE

\.0<. 5. 1.06 r '^ K 102 •' y\ if \ }/ S // \ /v " 1.02 ii.oo

5 '.00 -I ui V 5"« .* 098 h^- V ^' IOC lae ito wo tw toe J FMAMJ JASOND TOtAl LENOTHImml MONTHS

FIG. 5. Mean values of relative condition at different lengths (left) and in different months (right) in T. .\fystax. relative condition falls in April and rises in June-July. It falls in September in males, but rises in females. The peaks observed in January-March and June July mark the breeding time (Fig. 5). 220 HODA

DISCUSSION Rao and Girijavallabhan (1973) observed that the eggs of T. mystax occurred in all seasons of the year and were common in December-March. Venkataraman (1956) stated that its spawning season continued for 8 months, from September to May, but its maximum spawning was limited to November- March. Based on ova-diameter-frequency polygons, Dharmamba (1959) con­ cluded that T. mystax may have two spawning seasons a year, each fish spawn­ ing only once in a season. In the present study, ova-diameter-frequency polygons indicate two batches of maturing ova, suggesting that spawning occurs twice a year. Ihh has also been marked by the close approximation of GSI and relative condition.

Different species of Thryssa apparently mature at different sizes. For in­ stance, the average size at first maturity is 146-155 mm in T. hamiltonii (Masu- rekar and Rege 1960), 170 mm in T. purava (iPalekar and Karandikar 1952), 140-150 mm in T. mystax (Venkataraman 1956), 117 mm in T. baelama (Mari- chamy 1970) and 125 mm in T. dussumieri (Hoda 1976). In the present study, about 52% males and 47% females of T. mystax were mature at 140 mm- The maturation peaks at 140' mm in GSI, relative condition and percentage occurrence of maturity at different size groups confirm the observations that the attainment of minimum size for maturation and breeding is at 140 mm. This is in con­ formity with the observations of Venkataraman (1956) (Fig. 1 A-C). Fecundity in the genus Trissodes (Thryssa) shows variations. For in­ stance T. purava produces 5342-23878 eggs at 170-237 mm (Palekar and Karandikar 1952); T. hamiltonii, 12495-23060 eggs at 150-173 mm (Masu- rekar and Rege 1960); T. baelama, 1171-3556 eggs at 110-127 mm (Mari- chamy 1970); and T. dussumieri, 1585-7943 eggs at 106-139 mm (Hoda 1976). The fecundity of T. mystax, in this study, was 3581-24180 at 130-205 mm. In many fishes the fecundity increases by the power of 3 times the length or more as reported in haddock, Melanogrammus aeglefinus (Hoddar 1963), Sardinella longiceps (Balan 1966), Notopterus notopterus (Parameswaran and Siidia 1966) and T. dussumieri (Hoda 1976). In the present study, it is L^-^^^^- The fecun­ dity from the specimens of the same length, fish weight and gonad weight, varies considerably in this species, suggesting that the ova are shed in batches. This observation is in agreement with the observations of Kagwade (1970) on Poly- nemus heptadactylus and of Hoda (1976) on T. dussumieri.

ACKNOWLEDGEMENT I thank M|s Ghulam Hussain and Masoodul Haq of the Department of Statistics, University of Karachi, and Mr. S. M. Aqil Ahmad, Statistical Officer of the Glaxo Laboratories (Pakistan) Ltd., Karadii, for their guidance and help in the statistical analysis of the data. I also thank. Dr. William W. Reynolds, MATURATION AND SPAWNING OF ANCHOVY 221

Department of Biology, The Pennsylvania State University, Wilkes-Barre, Penny- sylvania, USA, for reviewing the manuscript. I gratefully acknowledge the faci­ lities provided by Prof. Dr. M. Nasima Tirmizi, Director of the Centre of Excellence in Marine Biology, University of Karachi.

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