To obtain a physiological activation agent containing a metabolic product of insulating sulfur bacteria as an active component, having excellent feed additive efficiency, easily producible by mass culture, having excellent preservability and exhibiting economical efficiency.

This agent contains a metabolic product of insulating sulfur bacteria [preferably belonging to the genus Chlorobium such as Chlorobium limicola (DSM245)] as an active component. The metabolic product can be produced by filtering the culture liquid of insulating sulfur bacteria to remove the bacterial cells and treating the filtrate containing the metabolic product and the medium component e.g. with a reverse osmosis membrane or an ultrafiltration membrane to remove the medium component. The culture of the bacteria is preferably carried out under a completely anaerobic condition at pH7.5-6.3 and 20-30°C under an illumination of ≥2,000 lux on the surface of the incubator. The objective physiological activation agent is added to a pisciculture feed preferably at a ratio of 1-50% as a cultivation liquid containing the metabolic product.