Histopathological evaluation of formalin toxicity in Arapaima gigas (Arapaimidae), the giant fish from Amazon

Abstract

This study aimed to determine the lethal concentration and the structural and ultra-structural effects caused by the formalin exposure on juveniles of Arapaima gigas. Ninety fish (60.1± 2.5g and 20.2±0.9cm) were exposed to 0, 22, 44, 66, 88 and 110mg L-1 in order to determine the lethal concentration (LC50-96h) that was 36.4mg L-1 of formalin. Sublethal effects were evaluated using histopathological analysis on the gills and assessment of behavioral alterations and clinical signs. The LC50 of formalin for 24, 48 and 72h was 88.3, 64.7 and 56.8mg L-1 respectively. Clinical signs and behavioral changes were found: erratic swimming, lethargy, crowding on the water surface, loss of hydrodynamic equilibrium, spasms and agonistic confrontation, which were observed only at 88 and 110mg L-1. The histological alteration index (HAI) showed that 66, 88 and 100mg L-1 presented significant difference (p<0.05) in relation to unexposed fish, indicating that moderate damage to the gills of fish exposed to formalin had occurred. The mean values of alteration (MVA) for 22, 44, 66, 88 and 110mg L-1 were 1.14, 1.29, 1.51, 1.53 and 1.60 respectively, and differences in this index were only observed with 110 mgL-1 of formalin. It is therefore possible to conclude that sublethal concentrations of formalin (22.0mg L-1) did not compromise the health of juveniles of A. gigas. Finally, concentrations greater than to LC50-96h may be carefully used for short-term exposure, since the MVA for all concentrations tested only indicated localized lesions that did not compromise gills functionality of exposed fish.

Antiparasitic efficacy and blood effects of formalin on Arapaima gigas (Pisces: Arapaimidae)

“…In contrast, for Haliotrema abaddon in the gills of Glaucosoma hebraicum with 25 mg L − 1 formalin during 10 and 24 h, there was no antiparasitic efficacy (Stephens et al, 2003). Arapaima gigas exposed to 22, 44, 66, 88 and 110 mg L − 1 formalin presented clinical signs and behavioral changes such as erratic swimming, lethargy, crowding on the water surface, loss of hydrodynamic equilibrium, spasms and agonistic confrontation, which were observed only at 88 and 110 mg L − 1 (Andrade-Porto et al, 2017). No mortality of A. gigas was observed whatsoever during the 1 h and 12 h therapeutic baths with formalin, since the lethal concentration for this fish was previously determined.…”

“…Nevertheless, as formaldehyde is a human carcinogen (Noordiana et al, 2011;Lai et al, 2016) and a toxic product, herbal medicines such as Mentha piperita have been assayed in order to control monogeneans in A. gigas (Malheiros et al, 2016). Therefore, formalin should be handled carefully during antiparasitic treatments in fish farming (Andrade-Porto et al, 2017).…”

“…In aquaculture, one of the ways to control and treat diseases so as to minimize economic losses has been the use of chemical products such as formalin (Yildiz and Pulatsu, 1999;Fajer-Ávila et al, 2003;Stephens et al, 2003;Sharp et al, 2004;Sitjà-Bobadilla et al, 2006;Fujimoto et al, 2006;Pahor-Filho et al, 2012;Paixão et al, 2013;Andrade-Porto et al, 2017). Nevertheless, formaldehyde has been classified by the International Agency for Research on Cancer (IARC) as a human carcinogen.…”

“…Recently, epidemiological studies have suggested that the exposure to this chemical can lead to the development of human hematopoietic cancers, such as leukemia (Lai et al, 2016). Safe concentrations of formalin recommended as a chemotherapeutic drug in baths for A. gigas have not been established (Andrade-Porto et al, 2017), and it has thus been used incorrectly and empirically in the aquaculture of this important Amazonian fish. Beyond that, therapeutic concentrations are used without taking the adequate exposure time, toxicity, tissue changes and accumulated residue in the muscle of treated fish into consideration (Jung et al, 2001;Andrade-Porto et al, 2017), as well as changes in homeostasis of animals exposed to it.…”

“…Safe concentrations of formalin recommended as a chemotherapeutic drug in baths for A. gigas have not been established (Andrade-Porto et al, 2017), and it has thus been used incorrectly and empirically in the aquaculture of this important Amazonian fish. Beyond that, therapeutic concentrations are used without taking the adequate exposure time, toxicity, tissue changes and accumulated residue in the muscle of treated fish into consideration (Jung et al, 2001;Andrade-Porto et al, 2017), as well as changes in homeostasis of animals exposed to it. Therefore, studies on the efficacy of formalin for A. gigas as well as their physiological and residual effects on the muscle are required.…”