Lengthâweight relationships (LWRs) of twelve fish species: Planilizaplaniceps, Planilizaparsia, Etroplussuratensis, Pseudetroplus maculatus, Oreochromis mossambicus, Gerres setifer, Scatophagus argus, Escualosathoracata, Carangoidspraeustus, Caranxheberi, Deveximentuminsidator, Nuchequllablochiiwere examined from Cochin estuary. Fish were caught between March 2019 to February 2020 by various gears like ring seine (mesh size of 8â26 mm), smaller mesh sized drift gill net (26â90 mm), cast nets with a (15-20 mm). Fish were gathered weekly from Munambam Fisheries Harbour (Lat. 10°1029653N, Long. 76°1022583E), Cochin Fisheries Harbour (Lat. 09°5623273N, Long. 76°1527643E) and Chellanam (Lat. 09°4729503N, Long. 76°1625513E). There are significance in all LWRs with r2 values those are ranged from 0.92 to 0.99 and b values are ranged from 2.61 to 3.37 (p < .001). The study provides new maximum length of E. thoracata.