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Reproductive Biology of the Indian SCAD, Decapterus Russelli (Ruppell, 1830) from Mangaluru Coast Ashwini

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Reproductive Biology of the Indian SCAD, Decapterus Russelli (Ruppell, 1830) from Mangaluru Coast Ashwini DOI 10.4010/2016.1751 ISSN 2321 3361 © 2016 IJESC ` Research Article Volume 6 Issue No. 6 Reproductive Biology of the Indian SCAD, Decapterus Russelli (Ruppell, 1830) from Mangaluru Coast Ashwini. L1, S. Benakappa2, H.N. Anjanayappa3, Akshay. L4 Department of Fisheries Resources and Management Karnataka Veterinary, Animal and Fisheries Sciences University, College of Fisheries, Mangalore, Karnataka, India [email protected] Abstract: Aspects of reproductive biology such as maturity, spawning season, sex-ratio and fecundity of Decapterus russelli were studied for a period of one year along the coast of Mangaluru. The length at which 50% of females of Decapterus russelli attained maturity was estimated at16-18 cm. The presence of mature, ripe and spent gonads was observed from August to May indicating prolonged spawning season. The sex-ratio (male: female) varied from 1:0.51 in the commercial catches, showing dominance of male in the population. Significant difference in the sex ratio was observed during all the months except during January and April. The absolute fecundity ranged from 71200 to 223680 eggs with an average of 140993 eggs per female. In the present study size of ova diameter ranged from 0.03 to 0.68 mm. Keywords: Decapterus russelli, Mangaluru, spawning season, fecundity, Sex-ratio, Gonado- Somatic Index. Introduction which 667 were male and 339 were female. The length, Fishes exhibit periodic or cyclic reproductive weight, sex and stage of maturity of individual fish in each behaviour. A thorough knowledge of maturation cycle will samples were noted. The ovaries were removed and preserved help to understand and predict the annual changes that a in 5% formalin for further studies. population undergoes. This involves morphological and Spawning season histological observation like changing pattern of the structure The spawning season was determined on the basis of and condition of the gonads are used to ascertain the maturity availability of mature gonads in commercial catches. The stages. The term maturity stages means the degree of ripeness Gonado - somatic Index (GSI) and relative condition factor of the gonad. Periodical microscopic and histological (kn) were also considered for assessing the spawning season. examination of testes and ovaries for at least one year helps in Size at first maturity understanding the progression and depletion of gonads The size at first maturity was determined plotting throughout the maturation cycle. Fish biologists have devised cumulative percentage of mature fish- III, IV, VI and VII schemes to identify maturity in different stages, usually 4 to stages in case of male and female against sizes (James and 5 or even up to 7 to 8 stages (Clark, 1934; Hickling and Badrudeen, 1981); (d) Methods Jayabalan (1986) and (e) Rutenberg, 1936; Prabhu, 1956; Qasim, 1973; Crossland, Udupa (1986). 1977). Gonado- Somatic Index Maturation refer to the cyclic morphological changes For calculating the Gonado - somatic Index, the weight that the male and female gonads undergo to attain full growth of the individual fish was noted and the gonads were removed and ripeness (Qasim, 1973) to understand those changes, it is carefully and weighed in an electronic after removing the also necessary to follow the regular and cyclic changes excess moisture using a blotting paper. (James, 1967; Baragi, undergone by the gonad. This can be best done by recognizing 1977). The Gonado – somatic Index was calculated using the the different phases in the cycle by assigning set of unique formula. GSI = Gonad weight/ Fish weight ×100. The average stages that identify the states of maturity of the gonads, as they GSI values wear plotted against months. pass through the different stages of development and spawn. Fecundity Thus, different maturity stages are assigned to the gonads, Fecundity was estimated gravimetrically using based on the well-defined criteria (Crossland, 1977). formalin preserved ovaries. The excess moisture was drained out and the ovaries were weighed to the nearest milligram. Materials and Methods Ovaries of the IV, V and VI stages were used for fecundity The present study on Decapterus russelli from estimation. A small sample from each ovary was removed and Mangaluru is based on a random samples of 1006 individuals weighed. The number of mature ova inn the weighed sample were collected fortnightly from fish landing center, individuals was counted. Fecundity was calculated form the number ova were ranging in size from 11 to 23 cm total length (TL) of for each individual by using the following formula. Fecundity = Numbers of mature ova in the sample X Total weight of ovary (g) Weight of the sample (g) Fecundity: length/weight/gonad weight-relationship Sex – ratio The relationship between fecundity and length of Sex – ratio was studied with respect to months and fish/weight of fish/ovary weight wear calculated using size groups of fish. Data on sex –ratio were analysed by x2 appropriate statistical methods. International Journal of Engineering Science and Computing, June 2016 7381 http://ijesc.org/ (chi-square) test to find out whether there was any percentage. In March and April all the stages were observed. dominance of either sex using following formula. Compared to March in April I and II the percentage of stage increased. In March III and V stages were dominant. In May 2 2 ᵡ 2 = (O M – E) + (OF-E) all the stages were observed except VI stage, percentage of II and IV stage decreased, while the percentage of stage I, III E E and V stages increased compared to previous month. Where, OM and OF = Observed number of male and female in the month respectively, E= expected number of male or female in a month, E= n/2. In case of female, stage III, IV and VI were recorded in August with dominance of stage III and IV and Results and discussion VI stage with similar percentage. In September and Spawning season November stages II, III, IV, V and VI made their The spawning season was determined on the basis appearance. Stage III and V were dominant in September of occurrence of individuals in mature, running, and spent month, and II and VI stage were dominant in November stages of maturity in each month. The seasonal changes in month. In October only III, IV, V and VI stages were the occurrence of gonads of Decapterus russelli in different present; III and IV stages were dominant. In December and stages of maturity are presented in Table 1. February all stages were observed, II and VII stages were dominant in December, while II and IV stages decreased in The results of the gonadal maturity of male during February. In January all stages were observed except V August showed only I, II, III, IV, and V stages. Stages I, II stage, the percentage of stage II, III, IV and VI decreased, and III were predominant. In September I, II, III, IV, and V while the percentage of stage I and VII increased. In March stages were present; I, II and III stages being predominant. In except stage I all stage were observed, stage IV and VI being October I, II, III, IV and V stages were present, II and III predominant. In April all stages were recorded I and III stage stages were dominant, but the percentage of stage III were dominant. In May only I, II, III, IV and V stages were increased compared to previous month. present; I stage being predominant, percentage of stages II, III, IV and V decreased compared to previous month. November showed only I, II and III stages but the Selvam et al. (2013) observed that Decapterus percentage of stage I and II increased compared to previous russelli eggs were observed during post monsoon, and months. In December only I, II, III, IV and VII were noticed; monsoon seasons. Manickasundaram (1990) noticed eggs stages II and III were dominant. In January, only stage I, II, during post monsoon season along Coleroon estuary and III and VII were present; I and II stages being predominant. Ramaiyan et al. (2005) observed these eggs in the monsoon In February only I, II, III, IV and VII stages were present; II and post monsoon seasons. stage was predominant and I and VII stages showed similar Table 1: Month wise percentage occurrence of gonads in different stages of maturity of D. russelli Months No. of Sex Maturity stages fish I II III IV V VI VII Aug.15 38 M 23.68 21.08 23.68 15.78 15.78 - - 12 F - - 83.34 8.33 - 8.33 - Sep. 71 M 28.57 34.28 24.28 2.85 10.02 - - 29 F - 13.79 31.05 10.34 24.14 20.68 - Oct. 72 M 4.16 25.02 54.16 12.5 4.16 - - 28 F - - 25.02 35.71 21.42 17.85 - 42 38.09 57.14 4.77 - - - - Nov. M 18 F - 33.33 16.67 11.11 16.67 22.22 - Dec. 135 M 14.94 45.52 33.58 1.49 - - 4.47 44 F 13.72 20.25 9.12 9.12 6.81 9.12 31.86 Jan.16 50 M 50.87 29.83 1.76 - - - 17.54 48 F 35.41 14.59 6.25 4.17 - 4.17 35.41 Feb. 78 M 22.03 50.84 3.38 1.69 - - 22.06 33 F 15.15 6.07 24.24 9.09 15.15 15.15 15.15 Mar. 53 M 7.54 11.32 22.64 11.33 33.96 1.88 11.33 47 F - 2.13 12.77 29.8 21.27 23.4 10.63 Apr. 61 M 49.19 27.87 4.91 11.47 1.64 3.28 1.64 40 F 30.00 15.00 20.00 12.5 10.00 5.00 7.50 May.
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