The study concerns evaluation of engagement of serotonergic system in the mechanisms of antimutagenic protection and survival under adverse conditions. It is shown that under long-term exposure to oil and industrial pollution, simultaneous sharp increase of mutations level in the erythrocytes and downregulation of serotonin-modulating anticonsolidation protein (SMAP; Mekhtiev 2000) in the livers of the sturgeon juveniles (Acipenser gueldenstaedtii persicus) is observed. Mutation level was evaluated by the micronucleus analysis and SMAP level-by the indirect ELISA-test utilizing anti-SMAP immunoglobulins. Intramuscular administration of SMAP leads to significant decrease of micronucleus amount in the erythrocytes of the sturgeon juveniles exposed to sediments polluted with PAH and heavy metals. Pre-conditioning of sazans by low dose of insecticide actara (100 mg/l) leads to upregulation of SMAP and to survival of all the animals in the experimental group, kept under high concentration of actara (400 mg/l), while all animals in the control group succumbed under these conditions. I.m. administration of SMAP prior to putting the sazans into the water containing high levels of actara (400 mg/l), in contrast to controls, leads to their total survival. Participation of serotonergic system in the mechanisms of antimutagenic protection and survival promotion under damaging conditions is concluded.