Abstract
Asian seabass (Lates calcarifer) farming in India largely follows a three-tier cage culture system, with fish harvested at approximately 1 kg body weight despite strong consumer preference for larger-sized fish (>2.5 kg). This study evaluated a fourth-tier fattening model aimed at bridging this market gap by extending the culture of 1 kg seabass for an additional short-duration grow-out phase in floating cages. Field trials were conducted in the brackishwater creeks of Vembanad Lake, Kerala, using 4 m × 4 m × 3 m HDPE–GI floating cages. A total of 300 seabass (1.0 ± 0.1 kg) were stocked at a density of 10 kg m⁻³ and reared for 120 days using low-value fish as feed.
The fattening model resulted in a mean final weight of 2.5 ± 0.2 kg, with a daily weight gain of 18 ± 2 g day⁻¹ and a specific growth rate of 0.96% day⁻¹. Survival was high (96.67%), and size uniformity at harvest was excellent (CV = 0.07). The feed conversion ratio was 5.06, acceptable for trash-fish-based feeding in short-cycle fattening operations. The total biomass harvested from the three cages was 3,160 kg.
Economic analysis demonstrated strong financial viability, with a benefit–cost ratio of 1.68, an internal rate of return of 66%, and a payback period of only 0.43 years. The model significantly reduced biological risk by bypassing early life stages while achieving a premium market size within a short culture period.
The results confirm that fourth-tier seabass fattening is a biologically efficient, economically profitable, and climate-resilient mariculture strategy. The model enables a dual-tier supply chain in which small-scale farmers exit at 1 kg. At the same time, specialized fattening units complete the final grow-out, thereby improving income, meeting market demand, and reducing pressure on wild seabass stocks.
Keywords: Lates calcarifer, seabass fattening, cage aquaculture, mariculture, fourth-tier farming, economic viability