Indian Journal of Geo-Marine Sciences Vol. 40(4), August 2011, pp. 516-521

Sex-ratio, maturation and spawning of the Indian , ilisha melastoma (: ) in coastal waters of Pakistan (northern Arabian Sea)

Khalid Mahmood , Zarrien Ayub* & Ghazala Siddiqui Centre of Excellence in Marine Biology, University of Karachi, Karachi-75270, Pakistan *[E-mail address: [email protected]] Received 22 March 2010; revised 5 December 2010

Present study showed that the over-all sex-ratio deviated in favour of females in Ilisha melastoma. However, the sex- ratio was approximately 1:1 in certain months while in others it was in favor of females. Similarly the sex-ratio deviated from 1:1 ratio in different size-classes. Minimum size at which the specimens of I. melastoma get matured is 14.9 cm in total length (11.5 cm in SL). Four maturation stages of ovaries, namely, immature, ripening, ripe and spent/recovering were recognized in I. melastoma. Two peaks of spawning were observed in this species, the major peak was from February to May and the minor peak appeared in August to November.

[Keywords: Maturation, spawning, Indian ilisha, Pakistan]

Introduction during the period March 2004 to February 2005 and a Species of the genus Ilisha are distributed in the total of 725 specimens of I. melastoma were Indo-Pacific region, i.e., Japan, China, Hong Kong, examined. Total length (cm) and weight (g) of each Singapore, Java, Borneo, Sumatra, Burma, India, fish was recorded. Fish was dissected from the Pakistan, Persian Gulf and Africa. According to abdominal region and the sex and gonadal maturity of Whitehead1 genus Ilisha have a circumtropical fish was determined by visual examination of gonads distribution in estuaries and coastal waters, with one (Table 3). For histological study, every month the species in the tropical east Atlantic, two in South ovaries of 20-25 fishes were fixed in Davidson’s America and eleven in tropical Asia. Genus Ilisha is Fluid for 48 hours. After fixation the ovaries were important in artisanal fisheries throughout the tropics transferred to 70% alcohol. Process of dehydration, of South and Southeast Asia, however little is known infiltration and embedding was followed as about the species belonging to genus Ilisha2-4. mentioned in Humason7. Embedded ovaries were Two species of genus Ilisha have been reported sectioned at 7 µm and then stained with Delafield’s from the coastal waters of Pakistan, I. melastoma and Haematoxylin and counterstained with Eosin. I. megaloptera5. Information on the reproductive For fecundity estimates, 33 ripe ovaries were biology of a species, such as length and age at first removed and weighed accurately by using electrical maturity, spawning season and fecundity are balance to nearest 0.01 g. From each ovary three important for effectively managing the fisheries for subsamples from anterior, middle and posterior region that species6. In the present study, the sex-ratio, of the ovary, weighing 0.1 g were preserved in 10% maturation and spawning of Ilisha melastoma (Bloch formalin for 5 days. Each and every ripe oocyte in the and Schneider, 1801) was studied based on subsample was counted under the binocular macroscopic and microscopic examination of gonad. microscope and the fecundity was estimated according to Hunter et al.8. Materials and Methods Samples of Ilisha melastoma were procured F = W/w × N monthly from the landings at Karachi Fish Harbour where F = Fecundity; W = Total ovary weight; ______w = subsample weight; N = no of oocytes in the *For Correspondence subsample. KHALID et al.: SEX RATIO, MATURATION AND SPAWNING OF THE INDIAN ILISHA MELASTOMA 517

The oocyte diameter was measured on the Deviation in sex-ratio could be due to partial histological sections with the help of an ocular segregation of mature forms through habitat micrometer. The diameter of oocyte was taken at one preferences11 due to migration12 or behavioral axis running parallel to the slide and the widest part of differences between sexes13 thus rendering one sex to the oocyte was measured. be more easily caught than another.

The 1:1 ratio of I. melastoma was found to be Results and Discussion disturbed in various size-classes (Table 2). Males Sex-ratios 2 showed preponderance in the size-class 14.0-15.9 cm Chi square (× ) was used to test whether the sex- 2 ratios observed were significantly different from the (X = 6.26; P < 0.05). Size-class 16.0-17.9 cm expected sex-ratio of 1:1. The overall sex-ratio of followed the ratio 1:1, while in the remaining size- I. melastoma was significantly in favour of females classes the 1:1 ratio was in favour of females (X2 = 25.98; P < 0.001) (Table 1). Month-wise (Table 2). Fish >24.0 cm showed the males and distribution of sexes fluctuated significantly in favour females approximately in equal numbers. Differences of females in May, June, August, and February while in the size-specific sex-ratio in fish have been related to sexual differences in growth, mortality or energetic in November it showed the preponderance of males 14-15 (X2 = 9.68; P = < 0.01). In the remaining months it cost of reproduction . followed 1:1 sex-ratio. In I. africana respectively Macroscopic examination of gonads from Nigeria and Ghana, the over-all sex-ratio did not 9-10 The sex of I. melastoma was determined on the differ significantly from the expected 1:1 ratio , visual examination of the gonads and four maturation however, the occurrence of more females in certain stages of male and female gonad of I. melastoma were months was related to the peak of their spawning 9 recognized, that is, immature, ripening, ripe and periods . Presence of more females of I. melastoma in spent/recovering whose characteristics are given in the present study in February, March, May, June, and Table 3. However, the sex of 44 specimens of August coincides with the peak of their spawning. I. melastoma could not be identified on macroscopic examination and the sex in these individuals remained Table 1  Chi square test of sex-ratios of I. melastoma in indistinct even on histological examination of the various months during the period from March 2004 to February 2005 (*P<0.05; **P<0.01; ***P<,0.001). gonad. Unsexed individuals of I. melastoma may be the spent condition of the gonad as has been reported Months Total Males Females Unsexed x2 March 23 11 12 - 0.04 Table 2  Chi square test of sex-ratios in different size-classes April 54 23 31 - 1.19 of I. melastoma obtained from the landings of Karachi Fish May 102 39 63 - 5.65* Harbour (*P<0.05; **P<0.01; ***P<,0.001) June 77 11 28 38 7.41** Size classes Total Males Females Unsexed X2 July 72 27 41 4 2.88 (cm) August 75 21 54 - 14.52*** September 60 20 39 1 6.12* 14.0-15.9 31 20 7 4 6.26* October 70 32 37 1 0.36 16.0-17.9 215 87 95 33 0.35 November 50 36 14 - 9.68** 18.0-19.9 291 120 166 5 7.40** December 61 29 32 - 0.15 20.0-21.9 145 33 110 2 41.46*** January 45 24 21 - 0.20 22.0-23.9 25 7 18 - 4.84* February 36 1 35 - 32.11*** 24.0-25.9 13 3 10 - 3.77 Total 725 274 407 44 25.98*** 26.0-27.9 5 4 1 - 1.80

Table 3 Macroscopic description of the maturity stages of the gonads of I. melastoma Stages Females Males Stage 1 (Immature) Translucent or whitish and thread-like, no White and thread-like, histological examination revealed oocytes visible, histological examination the sex revealed the sex Stage 2 (Ripening) Pinkish with blood capillaries, eggs appear as Whitish or creamish, size of gonad increased and can be whitish granules, size of gonad further increased recognized as male gonad as milt extruded on pressure Stage 3 or Ripe Pinkish or reddish, eggs distinctly visible, gonad Whitish with pink vascularization, gonad occupy ½ of occupy ½ of the body cavity the body cavity, milt running on pressure Stage 4 or Pinkish or reddish, eggs opaque, gonad shrinks Whitish, flaccid, gonad seems empty Spent/Recovering 518 INDIAN J. MAR. SCI., VOL. 40, NO. 4, AUGUST 2011

Fig. 1 Photomicrographs showing the developmental stages of the ovary in I. melastoma. A. Section of an immature ovary containing chromatin nucleolar and perinucleolar oocytes. B. Section of a ripening ovary showing perinucleolar oocytes and partially yolked oocytes. C. Section of a ripe ovary showing advanced yolked oocytes. D. Section of a spent/recovering ovary showing atretic oocytesb and perinucleolar oocytes. CN, chromatin nucleolar oocytes; PO, perinucleolar oocytes; PYO, partially yolked oocytes; AYO, advanced yolked oocytes; AO, atretic oocytes, Scale = 100 µm. by West16 that such gonads were probably ‘spent’ Size at first maturity of females ovary in which the egg production has ceased for the Smallest female of I. melastoma with ripe ovary current season and therefore, present problems in measured 14.9 cm in total length (11.5 cm in SL). The identifying. 18.0-19.9 cm size-class showed the greatest number 4 of I. melastoma with ripe ovaries. Blaber et al. Histological staging of female gonads reported that I. melastoma matured at about 100 mm Four arbitrary maturation stages of ovaries were SL and this size is smaller than the size (11.5 cm in recognized in I. melastoma on the basis of histological SL) obtained in the present study. Size of first sexual examination (Table 4 and Figure 1). maturity in females of some other Ilisha species KHALID et al.: SEX RATIO, MATURATION AND SPAWNING OF THE INDIAN ILISHA MELASTOMA 519

Table 4  Microscopic description of the maturity stages of the ovaries of I. melastoma. Stages Ovaries Stage 1 (Immature) Oogonia, chromatin nucleolar and perinucleolar oocytes are present. The perinucleolar oocytes had a large nucleus. Oocytes diameter ranges between 25-60 µm.

Stage 2 (Ripening) Partially yolked oocytes and perinucleolar oocytes present. The partially yolk ooyctes contained yolk granules and few yolk globules in their cytoplasm. Fig. 2Monthly percentages of ripe males and females Oocytes diameter ranges (based on macroscopic examination of gonads) of I. melastoma between 60-200 µm. from March 2004 to February 2005.

Stage 3 (Ripe) Advanced yolked oocytes are The spawning season is based on the presence of abundantly present. The cytoplasm of the oocytes are females with ripe ovaries. With the exception of filled with more yolk globules certain months the ripe females were found and few yolk granules. throughout the year (Figure 3). However, two peaks Oocytes diameter ranges of spawning were observed in I. melastoma, the major between 200-300 µm. peak from February to May and the minor peak from Stage 4 (Spent/Recovering) Ovary containing perinucleolar August to November. Marcus and Kusemuje9 reported oocytes. Few atretic oocytes that the ripe and ripe running females were caught in and post-ovulatory follicles can also be seen. all months indicating that the breeding occurred throughout the year in I. africana off the Lagos coast, Nigeria. However, the peak spawning was observed reported are for I. africana from Nigeria had 10 TL 11.7 cm (ref.9); I. kampeni matured at about 100 between May and December. Yankson and Azumah mm SL, I. megaloptera, I. elongata and had reported the major spawning season during I. pristigastroides matured between 100 and 200 mm January to May in I. africana off Cape Coast, Ghana. Previous studies have indicated that many clupeids SL while I. filigera matured at about 400 mm from 17-18 Sarawak, Malaysia4. While, Yankson and Azumah10 bred throughout the year . reported that the smallest mature female of I. africana In the present study the spawning season of from Ghana had TL 13.2 cm. I. melastoma based on the macroscopic examination Spawning season based on macroscopic of the gonads was in agreement with the spawning examination of gonads season, from February to May and from August to November, based on the histological examination of Males the gonads. However, the use of histology in maturity On the basis of the macroscopic examination of the studies has become more and more widespread as it is male gonads, it was found that ripe males of more consistent and reliable19. I. melastoma were present throughout the year with peak during September to November period (Figure 2). Fecundity Egg counts were made of females ranging in size Females between 17.5 to 25.7 cm in total length and On the basis of the macroscopic examination of the 48 to 123 g in weight. The fecundity ranged from female gonads, it was found that ripe females of 4392 to 32756 eggs. I. melastoma were present during the period from Relationship between fecundity and fish total February to May and from August to November length (TL) and fecundity and fish weight (W) was (Figure 2). estimated and described by the equation: Spawning season based on histological staging of female gonads F = aXb 520 INDIAN J. MAR. SCI., VOL. 40, NO. 4, AUGUST 2011

Fig. 3Monthly percentages of developmental stages of I. melastoma ovaries (based on microscopic examination) from March 2004 to February 2005. 1 = Immature stage; 2 = Ripening stage; 3 = Ripe stage; 4 = Spent/recovering stage. where F = Fecundity, X = an independent variable 1013 to 10600 eggs, respectively. In the present study “a” and “b” were estimated by using linear regression no significant relationship was found between as shown in the equations: fecundity and fish length or weight. According to Blaber et al.4 there is a positive relationship between F = 0.011 × TL4.675 fecundity and fish length in species of Ilisha. King20 had also conformed to this relationship in I. africana. 0.623 F = 995.4 × W According to Marcus and Kusemuje9 fecundity in I. africana increased with fish length and weight and There was no significant relationship between 2 the increment of fecundity relative to the length and fecundity and total length (r = 0.298; P > 0.05) and weight of fish were nearly isometric. fecundity and body weight (r2 = 0.030; P >0.05). In the present study the fecundity in I. melastoma The result of this study of I. melastoma will ranged from 4392 to 32756 eggs. The fecundity provide valuable information to the fisheries reported in the present study is greater than that of biologists and fisheries management authorities as Marcus and Kusemuje9 and Yankson and Azumah10 in this species has wide distribution from India to 1 I. africana which ranged from 2098 to 11687 and Indonesia and to Taiwan Islands . KHALID et al.: SEX RATIO, MATURATION AND SPAWNING OF THE INDIAN ILISHA MELASTOMA 521

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