Growth, Survival and Reproductive Responses of Pearl Spot ( <i>Etroplus suratensis</i> ) to Partial Fishmeal Replacement With Spirulina ( <i>Arthrospira platensis</i> ) in Coastal Pond Systems

Spirulina ( Arthrospira platensis ) is widely recognised in aquaculture as fish feed supplements for its exceptional nutritional value and bioactive compounds with immunostimulatory, antimicrobial and antioxidative properties. Despite its extensive use in aquafeeds, its effects on the growth, feed utilisation, survival and reproductive physiology of Etroplus suratensis as fish meal replacement in the fish diet remain inadequately studied. Fingerlings were stocked at 50 per in each replicate hapa and fed spirulina‐supplemented diets at SP0 (0%), SP25 (25%), SP50 (50%), and SP75 (75%) for 90 days. Fish fed the highest spirulina inclusion (SP75) exhibited a significantly greater final mean weight (42.41 ± 3.79 g) than the control group (25.60 ± 0.64 g) ( p &lt; 0.05). Weight gain, percentage weight gain and specific growth rate (SGR) increased significantly with higher spirulina levels, while feed conversion ratio (FCR) and protein efficiency ratio (PER) improved markedly. The condition factor showed no significant variation ( p &gt; 0.05). Moisture and crude protein contents increased with spirulina inclusion, whereas lipid content decreased significantly. Ash content was slightly higher in SP25, and carbohydrate levels declined. Significant dose‐dependent variations were recorded in hepatosomatic, stomach, gonadosomatic, and visceral indices, as well as in fecundity and ova diameter. Histological analysis revealed advanced oocyte development and accelerated gonadal maturation in SP75‐fed fish. The study concludes that spirulina supplementation significantly enhances both somatic growth and reproductive performance in E. suratensis , demonstrating its potential as an effective alternative to fish meal and other plant‐based feed supplements in aquaculture diets. A 50%–75% inclusion level is recommended for broodstock diets to improve growth and reproduction. Further research should evaluate the long‐term reproductive success and economic feasibility of spirulina‐based diets in aquaculture.