Indian Journal of Geo Marine Sciences Vol. 48 (04), April 2019, pp. 457-463 Biometric analysis of the flat needlefish Ablennes hians (Valenciennes, 1846) (Pisces: Belonidae) in the south-eastern Arabian Sea Subal Kumar Roul *1 , Rajan Kumar 1 , Ashok Kumar Jaiswar 2 , T. B. Retheesh 1 , A. R 1 Akhil, 1 D. Prakasan, U. Ganga 1 , E. M. Abdussamad 1 , Latha Shenoy 2 , & Prathibha Rohit 1 1 ICAR-Central Marine Fisheries Research Institute, Post Box No: 1603, Ernakulam North P.O., Kochi, Kerala, India 2 ICAR-Central Institute of Fisheries Education, Panch Marg, Off Yari Road, Versova, Andheri (west), Mumbai, Maharashtra, India *[E-mail: subalroul@gmauil.com] Received 08 September 2017; revised 09 January 2018 The study was aimed to investigate the relationship between various morphometric measurements and meristic counts and to establish the length-weight relationships (LWRs) and length-length relationships (LLRs) of flat needlefish Ablennes hians (Valenciennes, 1846) that were collected from longline fisheries in the south-eastern Arabian Sea between October 2015 and August 2017. Twenty-two morphometric measurements and four meristic counts of 173 specimens were examined for biometric analysis, and 350 specimens (45-122 cm TL, 90-2585 g TW) were analyzed for studying LWRs. Morphometric variables showed a significant correlation between the variables with the highest observed correlation between SL, FL and TL (r > 0.99). The descriptive statistics for all the meristic counts were found within the range provided by the earlier authors. A differential relative growth was observed across morphometric characters. Strong positive allometry was recorded for pectoral fin length, the height of dorsal and anal fin and pre-ventral length, whereas pronounced negative allometry was evident in case of morphometric variables from the head region. The LWRs showed similar growth pattern for male (b = 3.447) and female (b = 3.299) individuals. Therefore, the LWR was expressed for pooled data as W = 0.000321L 3.312 (R 2 = 0.929, p < 0.001). [Keywords: Length-length relationships; Length-weight relationships; Morphometric; Meristic; South-west coast] Introduction Morphometric and meristic characters are one of the easiest and frequently used methods for identification of species called morphological systematics 1 . The morphometric relationships between various body parts of fish are also used to assess the well-being of individuals and to determine possible differences between separate unit stocks of the same species 2 . Moreover, phenotypic markers are more suitable to study short-term, environmentally induced variation, which is perhaps most suitable for fisheries management 3 . Relationships between different types of lengths termed as length-length relationships (LLRs) are useful to convert several measures of body length 4,5 . Among them, total length (TL) – standard length (SL) relationship (LLR) is important for comparative growth studies, which is more applicable to estimate total length where only standard length is known 6 . In fishery science, length- weight relationships (LWRs) are generally used to estimate the average weight for a given length group and to convert length measurement into weight to give the estimate of biomass and yield, where technical difficulty is found in weighing the fishes 7,8 . The LWRs are also used as an important tool for biometric and morphological comparisons between different species in the same taxon and populations from different geographical area 9,10,11,12,13 . Thus, LWRs are important components of fisheries biology and an accurate estimate can be highly useful for fisheries management 8 . Needlefishes (family Belonidae) comprised 34 valid species in 10 genera all over the world 14 . The genus Strongylura with 14 species and Tylosurus with 6 species are among the two most diverse genera of the family. The needlefishes though mostly marine, 12 species are found in fresh waters and several species of Strongylura are reported to migrate a long distance into the freshwater area 14 . Being a pelagic group, needlefishes are found at the surface of the water. They are carnivorous in nature, mostly feed on small fishes captured by their beaks in a sideways fashion 15 . In India, the family has 9 species under 5 genera: One species each in Ablennes, Xenentodon, Platybelone and three each in Strongylura and Tylosurus 16 . Needlefishes are locally called as kolan