Reproductive and growth parameter estimation utilizing length-Stratified age samples of sandbird octopus (Amphioctopus aegina) near Phetchaburi Province, Thailand

This study aimed to analyze the growth parameters and age-length relationships of the sandbird octopus (<i>Amphioctopus aegina</i>) along the coast of Chao Samran Beach, Phetchaburi Province, Thailand. This included determining reproductive stages, the gonadosomatic index, and size at first maturity. A total of 1436 specimens comprising 782 males and 654 females were collected using octopus traps during January to December 2021. The mantle length and weight of each specimen were measured. Reproductive stages were assessed to determine the gonadosomatic index and size at first maturity, and growth parameters were estimated using the von Bertalanffy growth equation. Results showed that males exhibited a mantle length range of 3.1-7.5 cm (mean: 5.2 ± 0.7) and a weight range of 5.99-94.00 g (mean: 35.34 ± 11.24). Mantle length at first maturity for males was 4.2 cm, with full maturity at 7.0 cm. Females had a mantle length range of 2.8-9.4 cm (mean: 5.7 ± 0.9) and a weight range of 7.70-105.00 g (mean: 45.43 ± 17.00). Mantle length at first maturity for females was 5.9 cm, with full maturity at 7.5 cm. GSI values were highest in both sexes in February, April, May, June and November, suggesting reproduction occurred through much of the year, and females showed a large peak in May. GSI values were lowest in both sexes in September. The smallest recorded mantle length was 2.8 cm in May, and the largest was 9.4 cm in January. The specific values of t₀ for males, females, and both combined sexes were -0.017719, -0.014519, and -0.00672, respectively. These findings provide valuable insights into the growth and reproductive biology of <i>A. aegina</i>, which can inform sustainable management and conservation efforts for this species.