Feeding dynamics and reproductive biology of Indian mackerel Rastrelliger kanagurta (Cuvier, 1816) off Ratnagiri coast, India

Abstract

The feeding dynamics and reproductive biology of the Indian mackerel Rastrelliger kanagurta (Cuvier, 1816), along the Ratnagiri Coast, Maharashtra, were investigated during September 2024 to May 2025. A total of 830 individuals ranging from 5.9 to 27.3 cm total length (TL) were examined. Gut content analysis showed phytoplankton as the dominant dietary component, occurring in 82.4% of non-empty stomachs and contributing 48.75% of the food items, followed by zooplankton, which occurred in 67.1% of non-empty stomachs and contributed 31.2%. The relative contribution of phytoplankton and zooplankton varied among months, indicating seasonal variation in feeding composition. The overall male to female sex ratio was 1:1.46, with significant female bias observed in March and May. The length at first sexual maturity (Lm₅₀) was estimated at 20 cm TL for females. Monthly variation in the occurrence of mature, ripe and spent ovaries indicated reproductive activity throughout the study period, with a pronounced reproductive peak during March–May. Fecundity ranged from 12,657 to 132,739 oocytes per female, with a mean of 52,765 ± 5,020.3 oocytes per female. Keywords: Frequency of occurrence, Gut content analysis, Numerical method, Stomach contents