Is prophylactic formalin exposure a stress source for gilthead sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax)?

Stress in gilthead sea bream (Sparta aurata) and sea bass (Dicentrarchus labrax) externally exposed to formalin was evaluated by measuring stress indicators; plasma cortisol, glucose, calcium (Ca), phophorus (P), sodium (Na), potassium (K), chloride (Cl), magnesium (Mg), hematocrit, and innate immunity parameters; C-reactive protein (CRP), ceruloplasmin. Fish were separately exposed to formalin at a concentration of 150 ppm for 60 min. The parameters were analyzed for sea bream and sea bass exposed to antimicrobial agents soon after treatment and fish exposed to antimicrobial agents after 24 h and 48 h (recovery) following the treatments. Plasma cortisol levels increased after exposure in both sea bream and sea bass however, plasma cortisol recovered in sea bass within 48 h. Plasma glucose values in exposed sea bream and sea bass were 2-fold and 3-fold higher than controls, respectively. Plasma glucose values remained high in 48 h recovery. Plasma electrolytes after exposure and during recovery showed fluctuated results, with different time profile and fish species. While plasma P, Mg and Cl were not affected by formalin exposure in sea bream, plasma Na and Cl remained unchanged in sea bass exposed to formalin. Hematocrit values in sea bream and sea bass did not change after fonnalin exposure. Innate immunity parameters measured in this study; C-reactive protein (CRP) and ceruloplasmin changed after formalin exposure. CRP levels in sea bream decreased after exposure and did not return to control values in recovery period. However, CRP levels in sea bass increased soon after exposure and decreased to control levels within 48 h recovery. Ceruloplasmin values decreased after formalin exposure both in sea bream and sea bass and did not return to control values within 48 h recovery. The results demonstrated that formalin exposure represents potentially stressful event for sea bream and sea bass when considered the elevated plasma cortisol, glucose, disrupted hydromineral balance, altered CRP and ceruloplasmin.