J Appl Ichthyol. 2017;1–2. wileyonlinelibrary.com/journal/jai | 1 © 2017 Blackwell Verlag GmbH Received: 25 February 2017 | Accepted: 4 July 2017 DOI: 10.1111/jai.13441 TECHNICAL CONTRIBUTION Length-weight relationship of Thryssa malabarica (Bloch, 1795) and Thryssa dayi Wongratana, 1983 from Kerala, southwest coast of India S. K. Roul | T. B. Retheesh | D. Prakasan | E. M. Abdussamad | P. Rohit ICAR-Central Marine Fisheries Research Institute, Cochin, Kerala, India Correspondence Subal Kumar Roul, ICAR-Central Marine Fisheries Research Institute, Cochin, Kerala, India. Email: subalroul@gmail.com Summary The present study reports the length-weight relationships (LWRs) of two clupeoid fish species, Thryssa malabarica (Bloch, 1795) and Thryssa dayi Wongratana, 1983 from Kerala waters, southwest coast of India during the period October 2015 to September 2016. Altogether 88 specimens of T. malabarica and 97 T. dayi were collected on weekly basis from gill nets (mesh size, 2.6–5.0 cm) and ring seines (mesh size, 0.8– 2.6 cm) during the period. The value of parameter b in the equation of LWRs was esti- mated as 3.237 and 3.248 for T. malabarica and T. dayi respectively. 1 | INTRODUCTION Information on length-weight relationships (LWRs) are important for estimation of weight, biomass and yield when only length measure- ments are available (Froese, 1998, 2006). LWRs are also important for biometric and morphological comparisons not only between different species in same taxon but also between populations from different geographical area (Duan & Tan, 2016; Hossain et al., 2016; Kumar, Chakraborty, Jaiswar, Sandhya, & Panda, 2012; Panda et al., 2016; Shah et al., 2014). Thryssa malabarica (Bloch, 1795) and Thryssa dayi Wongratana, 1983 are mostly marine, schooling, and inshore pelagic fish species. Thryssa malabarica found all along the Indian Coast, whereas T. dayi mostly restricted to the west coast of India (Froese & Pauly, 2017). They form a small scale clupeoid fishery along the coast having local demand only. However, their basic biological information, LWRs is lacking. The present study aims to provide the first information on LWRs of T. malabarica and T. dayi, from the Cochin waters, southwest coast of India. 2 | MATERIALS AND METHODS Fish specimens were collected randomly on weekly basis, represent- ing various length group from two landing sites (Kalamukku: Lat. 09°59′924″N, Long. 76°14′564″E and Chellanam: Lat. 09°47′950″N, Long.76°16′551″E) of Cochin coast, Kerala, southwest coast of India, from the commercial catch during October 2015 to September 2016. The fishes were caught by gill net of different mesh size (2.6–5.0 cm) and ring seine (0.8–2.6 cm mesh size) of the region. Collected speci- mens were immediately ice packed on site and brought to the labora- tory for further studies. The identity of the species was confirmed according to Whitehead, Nelson, and Wongratana (1988). The length measurements such as total length (TL), fork length (FL), standard length (SL) were taken using a digital vernier calliper with 0.1 cm ac- curacy and total body weight (BW) by an electronic weighing balance with 0.01 g accuracy. The LWRs were calculated using the equation: TW = aTL b (Froese, 2006; Le Cren, 1951) and logarithmically trans- formed into log TW = log a + b logTL, where TW is the total weight (g), TL is the total length (cm), and a and b are the regression parameters. The statistical significance level of co-efficient of determination (r 2 ) and the 95% confidence limits of parameters a and b (CL 95%) was estimated by least square linear regressions performed with the trans- formed equation. Extreme outliers were removed from the regression analyses according to Froese (2006). 3 | RESULTS A total of 185 specimens belonging to 88 T. malabarica and 97 T. dayi were analysed. Sample size, total length range (cm) and body weight range (g), LWRs parameters with 95% CI of a and b, and