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REPRODUCTIVE BIOLOGY OF SHORT brachysoma (Bleeker, 1851) AND R. kanagurta (Cuvier, 1817) IN THE SOUTHERN

Thanate Sritakon Niracha Songkaew Songrit Chotithammo and Somjai Vechprasit Southern Marine Fisheries Research and Development Center, 79/1 Wichianchom Rd., Bo-Yang, Muang, Songkhla 90000, Thailand

ABSTRACT

Short mackerel (Rastrelliger brachysoma) and indian mackerel (R. kanagurta) were sampled in the southern Gulf of Thailand during December 2003 and February 2005 from mackerel gill net, purse seine and pair-trawlers for the study of length-weight relationship, total length-standard length relationship, spawning season, size at first maturity and sex ratio. Length-weight relationship and total length-standard length relationship of short mackerel, the length of which was 13.5-24.5 cm, were W = 0.0260TL2.7379 and TL = 0.4825+1.1958SL, respectively. Their spawning season was found all year round with 2 peaks : December - February and May – August. Size at first maturity of male and female short mackerel were 16.02 and 16.84 cm, respectively. Their monthly sex ratio of male and female ranged from 1:0.83 to 1:2.39. For indian mackerel, the length of which was 16.5-26.3 cm, their length-weight relationship was W = 0.0422TL2.5804. Their total length-standard length relationship was TL = -0.5576+1.2483 SL. Their spawning season was found all year round with 2 peaks : January - April and July - November. Size at first maturity of male and female indian mackerel were 19.51 and 20.84 cm, respectively. Their monthly sex ratio of male and female ranged from 1:1.00 to 1:2.90.

Keywords : Reproductive biology, Rastrelliger brachysoma, Rastrelliger kanagurta, southern Gulf of Thailand