Use of formalin in intensive aquaculture: properties, application and effects on fish and water quality

Abstract

Formalin (aqueous solution of formaldehyde stabilized with methanol) is one of the most used disinfectants in aquaculture. It is used to eliminate infectious agents but may be responsible for negative effects on fish and water quality. This work focuses on physical–chemical properties of formalin and on its reactions and its use in intensive aquaculture and in environment. The types of treatments and the action mode of formalin are also described. The main consequences of formalin exposure to fish are damage in gills and alterations in mucous cells. Formalin also interacts with some treatments adopted in aquaculture establishments, for example biological filter, where the nitrification process seems to be strongly affected. With respect to formalin inactivation, formaldehyde (effluent) may be diluted with water or specific treatments should be conducted to decrease the concentration levels before its discharge into the environment. The common methodologies applied to aquaculture are not completely efficient on formalin removal from water, and the advanced oxidation processes may be a good alternative.

Oxytetracycline in intensive aquaculture: water quality during and after its administration, environmental fate, toxicity and bacterial resistance

“…This parameter is an indicator of acute toxicity (inversely correlated) and corresponds to the concentration able to kill 50% of exposed organisms (Leal et al . ). Murphy and Peters () classified oxytetracycline hydrochloride as practically nontoxic to Rainbow Trout ( Oncorhynchus mykiss ), obtaining values of LC 50 (96 h) equal to 116 mg L −1 .…”

“…Bio‐filtration occurs through nitrifying bacteria, promoting the nitrification of ammonia (NH 4 + ) and nitrites (NO 2 − ) into nitrates (NO 3 − ) (Leal et al . ). Ozonation kills or inactivates pathogens and promotes the oxidation and degradation of organic compounds.…”

“…It may be practised in open circuits (flow‐through systems), as well as in closed and semiclosed circuits (recirculated/reused water systems) (EC ; Leal et al . ). In closed and semiclosed circuits, prior to water re‐enters in the tanks of fish production, water treatment processes are adopted.…”

Paraprobiotics: an aquaculture perspective

“…Formalin (37% aqueous solution of formaldehyde gas) is one of the most commonly used disinfectants in the aquaculture sector (Leal et al . ). Formaldehyde inactivates microorganisms by alkylating the amino and sulfhydral groups of proteins and ring nitrogen atoms of purine bases (Favero & Bond ).…”

Toxicity of formalin for juvenile Centropomus viridis and in vitro efficacy against the parasite Rhabdosynochus sp. (Monogenea: Diplectanidae)

“…Formalin has been authorized by the Food and Drugs Administration (FDA) for use in immersion baths for ectoparasite control in aquaculture. The product can be applied in short baths at concentrations up to 170 mg/L for up to 1 hr for water temperatures above 10°C, or in prolonged baths at concentrations between 15 and 25 mg/L for 12 hr (see Leal et al, 2018). Even though formalin can have negative effects on fish and water quality, it remains one of the most effective therapeutic treatments in aquaculture.…”