FORMALIN USE IN FRESHWATER FISH FARMING
Formalin is used in animal health as an inactivating agent in the manufacture of vaccines but also for its biocidal properties for the disinfection of premises and livestock equipment. It is also used to prevent and treat diseases, especially in aquatic production for ectoparasitic flagellates, however few data are available on its usage. Formaldehyde classification as carcinogen in the European regulation since 2014 now requires the search for substitutes.
As a part of a study on health practices, a representative sample of 101 freshwater fish farms was investigated in France in 2014. A questionnaire on the veterinary products used in connection with the housing structure, husbandry practices and sanitary status was completed during an on-farm visit.
Sixty four percent of the farms used formalin, mainly as a preventive or curative measure against parasites (87% of uses), with the objective of maintaining the parasite population at an acceptable level to the fish. The use of formalin was significantly associated with a higher frequency of parasitic diseases reporting. Ichtyobodo necator infections were the first reason reported for the use (39%) of formalin. This parasite is very widely encountered in freshwater salmonid farms and is responsible for cutaneous and branchial lesions causing frequent bacterial superinfections. Formalin was more commonly used on mixed farms with nursery and on-growing stages (71% of users in this category) than on farms specialized in on-growing (52% of users in this category). Fish farms more often rear young fish, from eggs to frying stages. Rainbow trout fry syndrom reports were also more common in user fish farms. Wearing protective equipment for formalin handling was limited and mostly consisted in wearing gloves (69%).
In specific sanitary conditions the use of formalin is deemed to be essential, due to the lack of effective alternative. To secure its use, protective measures must be defined and adopted to minimize exposure of the workers.