Int. J. Aquat. Biol. (2015) 3(6): 372-378 E-ISSN: 2322-5270; P-ISSN: 2383-0956 Journal homepage: www.ij-aquaticbiology.com © 2015 Iranian Society of Ichthyology Original Article Reproductive biology, maturation size and sex ratio of black tiger shrimp (Penaeus monodon Fabricius, 1798) from fishing grounds of Digha coast, West Bengal, India. Naser Uddin Sk1, Shubhadeep Ghosh1, Joydev Maity*21 1Regional Centre of Central Marine Fisheries Research Institute (ICAR), Visakhapatnam - 530 003, Andhra Pradesh, India. 2Department of Aquaculture Management and Technology, Vidyasagar University, Midnapore - 721 102, West Bengal, India. Article history: Received 1 September 2015 Accepted 27 N o v e m b e r 2015 Available online 2 5 D e c e m b e r 2015 Keywords: LM50 Spawning season GSI Abstract: The present paper studies the reproductive biology, maturation size and sex ratio of Penaeus monodon collected from Digha fishing grounds, India during 2011-2013. A total of 633 individual of P. monodon were examined and among them 242 were males and 391 were females. The overall yearly sex ratio was observed to be 1:1.6 (males: females). Based on the results, the spawning season of P. monodon was mainly in January-February and was extended up to June. The first maturity was observed at 163.5 mm length. The estimated number of ova in the mature ovary ranged from 120155 to 961240 in P. monodon. Introduction Penaeus monodon is the largest species among the penaeids prawns commercially known as Jumbo Tiger Prawn or Black Tiger Prawn. It is widely distributed and commercially very important species in India and national market. Rao (2000) studied the reproduction and the spawning of P. monodon and reported it to be heterosexual as is the case with all the penaeids. The females attain maturity at 196-200 mm and males at 166-170 mm TL. The five maturity stages distinguished in the ovary could be termed as immature, maturing, mature, ripe and spent. Fecundity varies from 200000 to 1000000 eggs depending on the size of the females. Spawning takes place in the sea at 40-80 m depth. Knowledge of spawning seasons and distribution of spawning areas are important for the management of fisheries The spawning seasons of penaeid shrimps are most commonly determined by the percentage of mature females present in the catch or from the changes in gonadal indices (Crocos and Kerr, 1983; Garcia, 1985; Bauer and Vega, 1992; Crocos and Coman, 1997; Minagawa et al., 2000; Crocos et al., * Corresponding author: Joydev Maity E-mail address: jmaity@mail.vidyasagar.ac.in 2001; Costa and Fransozo, 2004; Aragon-Noriega and Garcia-Juarez, 2007). In the Philippines, spawning is year round but there seems to be two peak seasons in a year. February-March or July and October-November, although it varies from year to year (Motoh, 1981). Rajyalakshmi et al. (1985) reported the peak season as October–April corresponding to the post-monsoon season coinciding with an increase in the salinity along the Odisha cost, while it varies from place to place in Philippine and Taiwan (Su and Liao, 1986). Su et al. (1990) observed September-December as the peak season. However, there is no published information available till date on the breeding season, size at sexual maturity and sex ratio of P. monodon from Digha coast of West Bengal, India. The present study is to provide information on the reproductive biology including the breeding season, size at sexual maturity and sex ratio of P. monodon in coastal waters of Digha coast, India. Materials and Methods The samples of P. monodon were collected from 373 Uddin Sk et al./ Reproductive biology of black tiger shrimp from West Bengal, India commercial catches of Digha Mohana landing centre caught by trawlers from Bay of Bengal of West Bengal coast during 2011-2013. Shrimps with petasma and presence of spermatophores in the terminal ampoule were taken as matured males. In females, the ovaries were classified into immature, early maturing, late maturing, mature and spent- recovering stages based on the size, colour and yolk formation (Primacera, 1989) Specimens with immature, spent-recovering and early maturing ovaries were rated as immature while those with late maturing and mature ovaries were considered as matured ones. The gonads were cut open on the dorsal side and removed to observe its condition. The weight of gonad was taken by using electronic balance to the nearest 0.001 g. The gonads were preserved in 7% formalin for further analysis. Sex ratio: The sex ratio is based on the monthly estimated number as to get an actual representation of males and females in the population. Homogeneity of the sex ratio (based on observed numbers) over months in three years has been tested using Chi-square test (Snedecor and Cochran, 1967). This is computed as follows: X2 = ∑ (O-E)2 / E Where, O = observed number of males and females in each month/length group, and E= expected number of males and females in each month /length group. Significance at probability level of P = 0.05 was carried out. Homogeneity was tested for 1:1 ratio. Length at first maturity (LM50): Sex was determined and stages were classified as immature, early maturing, late maturing, mature and spent (Dall et al., 1990). The maturity classification was made (Farfante, 1969) where stages III and above were considered to be mature for males and females, respectively. For both males and females, the size at first maturity was determined by calculating the proportion of mature individuals in each size class (carapace length and total length). The size at which 50% of individuals were mature was taken as the length at first maturity (LM50) (King, 1995). Spawning season: To determine the spawning season, proportion of the gravid and ripe females (IV and V) in each month were observed and the highest percentage were taken to determine the spawning period. Ganado somatic Index (GSI): The spawning season of P. monodon was estimated from the mean index value of gonad in different months of the year. For gonado-somatic index (GSI) estimation, females were weighed individually after wiping it dry. The gonad was dissected out carefully and weighed by using an electronic balance. The GSI are calculated by using the formula: GSI = (Weight of the gonad x 100)/ Weight of the fish. Fecundity: For studying the fecundity, the preserved ovary was washed and dried by placing it between two blotting papers. The ovary sub-sample was taken from the anterior, middle and posterior regions of the ovary. The weight of ovary was recorded, and all sub-samples of the ovary were weighed to the nearest 0.001 g. using an electronic balance. The mature ova present in the sub-samples were counted by using a counting slide. From the number of ova in the weighed sub-sample, fecundity was calculated using the formula: Fecundity = (total weight of the ovary/weight of the sample) × number of ova in the sample The relationship between the fecundity to total length, total weight and ovary weight were found out by fitting regression on logarithms of observed values by least square method (Snedecor and Cochran, 1967). F= αXb Where, F = Fecundity, 𝛼 = constant, X = variable (total length, body weight or ovary weight) and b = correlation coefficient. The exponential relationship was transformed into a straight line logarithmic form based on the equation: Log F = log 𝛼+ b log X. Results Sex ratio: During 2011-2013, total numbers of 631 specimens of P. monodon were examined, of them 242 were males, and 391 were females. The sex ratio is presented in Tables 1 and 2. The overall yearly sex 374 Int. J. Aquat. Biol. (2015) 3(6): 372-378 ratio was observed to be 1:1.6 (males: females). A chi-square test showed that the annual distribution of females and males is not significantly difference from 1:1 ratio at 0.05% level (P>0.05), although the sex ratio varied from month to month during the study period. Spawning season: Average gonadosomatic index of females of P. monodon is presented in Figure 1. In the present study, GSI was observed to be higher between January and July. The maximum value (GSI=10.36) was observed in June and minimum value (GSI=7.8) in October. The GSI of females of P. monodon showed two peaks, in the months of January and June. The highest GSI of 10.36 in June, indicating that most females were mature. The percentage of mature females is presented in Figure 2. The highest mature percentage was observed in the month of February (88.89%) and June (85.4%). The lowest percentage was observed in the month of September (65.2%). Mature females in all months were observed to be >50% indicating that P. monodon spawns more or less throughout the year. LM 50: The length at first maturity is presented in Figure 3. In the present study, 163.5 mm was 2011 2012 2013 Month Male Female d2/e Sig Male Female d2/e Sig Male Female d2/e Sig Jan 10 9 0.026 S 8 13 0.595 S Feb 14 9 0.543 S 9 11 0.1 S 11 16 0.463 S Mar 6 7 0.038 S 6 15 1.929 S Apr 0 0 0 S 5 5 0 Jun 3 14 3.559 S 5 21 4.923 NS 13 13 0 S Jul 4 11 1.633 S 5 10 0.833 S 19 9 1.7857 S Aug 3 19 5.818 NS 8 18 1.923 S 4 17 4.0238 NS Sep 5 20 4.5 NS 11 13 0.083 S 6 13 1.2895 S Oct 4 23 6.685 NS 13 8 0.595 S 11 9 0.1 S Nov 4 12 2 S 7 21 3.5 S 19 5 4.0833 NS Dec 4 21 5.78 NS 14 15 0.017 S 11 14 0.18 S S=Significant, NS=Not significant Table 1. Annual sex ratio of P. monodon during fishing period of 2011-2013. Month Male Female Total chi squre value Significant F/M Jan 18 22 40 0.2 S 1.222222 Feb 34 36 70 0.028571 S 1.058824 Mar 12 22 34 1.470588 S 1.833333 Apr 5 5 10 0 S 1 Jun 21 48 69 5.282609 NS 2.285714 Jul 28 30 58 0.034483 S 1.071429 Aug 15 54 69 11.02174 NS 3.6 Sep 22 46 68 4.235294 NS 2.090909 Oct 28 40 68 1.058824 S 1.428571 Nov 30 38 68 0.470588 S 1.266667 Dec 29 50 79 2.791139 S 1.724138 Total 242 391 633 17.53633 NS 1.615702 S=Significant, NS=Not significant Table 2. Month-wise sex ratio of P. monodon during fishing period of 2011-2013. Figure 1. Average gonadosomatic index (GSI) of P. monodon females from Digha coast during 2011 – 2013. 375 Uddin Sk et al./ Reproductive biology of black tiger shrimp from West Bengal, India observed as the length at first maturity. Fecundity: In the present study, length and weight of mature females of P. monodon ranged from 125- 250 mm and 47-261 g, respectively. The estimated number of ova in the mature ovary ranged from 120155 to 961240 in ovary weight ranging 5 to 40 g. The relationship between fecundity and length and fecundity and weight of P. monodon was Log F= 1.295461+3.135046 LogL (r=0.607847) and Log F= 3.253808+1.022533 LogW (r= 0.58288). There was significant variation (P<0.05) in the slope of regression relations of body length and weight with fecundity. Discussion In the present study, the observed sex ratio was 1:1.6 (males: females). This could be attributed to changes in the fishing ground and fishing pattern of trawl nets and the pattern of migration during breeding seasons of both sexes. In general, sex ratio is known to be close to 1:1 (males: females) in nature (Fisher, 1958). Costa et al. (2010) suggested that the sex ratio of females may be related to the greater vulnerability of females to fishing due to their size. Sarada (2010) observed from Kozhikode, Kerala, India on the annual sex ratio between male and female to be 1.07:1. Two peak spawning seasons were observed with the highest mature percentage of females in February and June. The results of GSI indicated the spawning season to be during January-February and June. Similar results were reported by Khan et al. (2003) who observed the spawning season of P. monodon twice a year i.e. during winter (February) and summer (September). Along the Kakinada coast, the species spawns throughout the year with different peak periods in different years. Rao (2000) observed a similar phenomenon in the spawning off Visakhapatnam. Amanat and Qureshi (2011) observed the peak spawning activity from the coastal waters of Pakistan during August to October with a secondary peak during February to March. Shrimps exhibit more than one spawning period in a year. The process of ovarian maturation goes through different reproductive stages viz., undeveloped, developing, nearly ripe, ripe and spent. After completion of first spawning, shrimps rest in a developing stage before going through the maturation cycle again (Jayawardane et al., 2003). The estimated number of ova in the mature ovary ranged from 120155 to 961240. Fecundity depends on the size of females. Babu (2014) observed the fecundity at 723251 for 270 g from Bhairavapalem (A.P) India, which slightly varies from the results of the present study. This may be due to differences of environment and on the availability of food. Fecundity increased with prawn size, suggesting that much of the available energy in larger prawns is devoted to egg production rather than growth. Motoh (1981) established a positive correlation between Figure 2. Average maturity percentage of P. monodon females from Digha coast during 2011-2013. Figure 3. Length at first maturity (LM50) of P. monodon females at Digha coast, India. 376 Int. J. Aquat. Biol. (2015) 3(6): 372-378 fecundity and female size of P. monodon in terms of carapace length. Villegas et al. (1986) demonstrated a positive correlation between fecundity and spawner weight of P. monodon. Primavera (1989) stated that fecundity or number of eggs of P. monodon in a complete spawning averages 300000 (range: 100000-800000) for ablated females and 500000 (range: 200000-1 million) for wild spawners. Length at first maturity was observed at 163.5 mm in the present investigation. The results differ from Rao (2000), who studied the reproduction and the spawning of P. monodon from Kakinada, possibly because of differences in food, temperature and water quality, impacting maturity. According to Rao (2000), the females attain maturity at 196-200 mm and males at 166-170 mm TL. 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(2015) 3(6): 372-378 E-ISSN: 2322-5270; P-ISSN: 2383-0956 Journal homepage: www.ij-aquaticbiology.com © 2015 Iranian Society of Ichthyology چکیده فارسی ,Penaeus monodon Fabriciusشناسی تولیدمثل، اندازه بلوغ و نسبت جنسی میگوی ببری سیاه )زیست طق صیادی سواحل دیقا، بنگال غربی، هندوستانادر من (1798 2جویدو مایتی ،2قش شوبهادیپ ،1ناصر الدین س.ک. .هندوستان ،آندراپرادش ،353335ویساخاپاتنام ،ای انستیتو تحقیقات شیالت دریاییمرکز ناحیه1 .هندوستان ،بنگال غربی ،221132میدناپور ویدیاساگار، دانشگاهپروری، مدیریت و تکنولوژی آبزی گروه2 چکیده: 2311طی سال هندوستان دیقا، صیادیمناطق صید شده از Penaeus monodon، اندازه بلوغ و نسبت جنسی شناسی تولیدمثلزیست حاضر الهقم نسبت جنسی عدد ماده بودند. 591عدد نر و 242ها مورد بررسی قرار گرفت که از آن P. monodonنمونه 355کند. تعداد مطالعه می 2315الی بود و تا های ژانویه و فوریهطور عمده ماهبه P. monodonفصل تخمریزی ،اساس نتایجبر)نر به ماده( بود. 3/1به 1مشاهده شده در دوره مطالعه 123133 در محدوده های بالغدر تخمدان نمونهتخم متری مشاهده شد. تعداد تخمینی میلی 3/135ماه ژوئن نیز ادامه داشت. نخستین بلوغ در طول عدد بود. 931243تا .GSI، فصل تخمریزی ،50LC :کلمات کلیدی