Statolith growth increments were analysed in the bigfin reef squid, Sepioteuthis lessoniana lineage B, for estimating the age and growth in the Gulf of Mannar Biosphere Reserve (GOM), southeast coast of India. The identification of S. lessoniana lineage B was determined by mitochondrial cytochrome c oxidase I gene sequence. The statolith increment age analysis indicated that the wild-captured squid population of S. lessoniana in the study area undergoes rapid growth. The age of S. lessoniana in males ranged from 61 (95 mm dorsal mantle length (DML)) to 220 d (390 mm DML), while it was 64 (98 mm DML) to 199 d (340 mm DML) in females. The average daily growth rate in males and females was 1.63 and 1.55 mm DML d−1, respectively. The instantaneous growth rate varied from 0.85 (210 d) to 4.1% (110 d) for males and 0.65 (190 d) to 3.7% (110 d) for females. The age at first maturity was 114 and 120 d for males and females, respectively. Back-calculated hatching dates and the attainment of maturity in females suggested that the reproduction of S. lessoniana is year-round, with two distinct spawning peaks during July–August and February months; accordingly, the hatching dates were spread throughout the year, with the presence of two cohorts. Based on the statolith data, it can be concluded that S. lessoniana lineage B in the GOM has a potential lifespan of up to 7 months. This finding contradicts the previous growth estimates based on length-frequency data, which underestimated the true growth potential of this species.

Growth, which is intrinsically linked to environmental conditions including temperature and food availability are highly variable both temporally and spatially. Estimates of growth rates of the Southern Ocean euphausiid Thysanoessa macrura are currently restricted to limited studies which rely upon repeated sampling and length-frequency analysis to quantify growth rates. The instantaneous growth method (IGR) was used to measure the growth rate of T. macrura successfully in the southern Kerulen Plateau region during summer, providing the first IGR parameters for the Southern Ocean euphausiid species. Results of the four-day IGR incubation indicate a period of low somatic growth for adult T. macrura. Males had a longer intermoult period (IMP) (62 days) than females (42 days), but the sexes exhibited similar daily growth rates of 0.011 mm day−1 and 0.012 mm day−1 respectively. Juveniles exhibited the fastest growth, with an IMP of 13 days and daily growth rate of 0.055 mm day−1 indicating a prolonged growth season, similar to the Antarctic krill E. superba. Consequently, we highlight the usability of the IGR method and strongly encourage its use in developing a comprehensive understanding of spatial and seasonal growth patterns of T. macrura.