Putative poison gland in Acanthodoras spinosissimus

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Putative poison gland in Acanthodoras spinosissimus

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SODRÉ, J. G., COLAÇO-FERNANDES, T. R., PY-DANIEL, L. H., BIRINDELLI, J. L., & ZUANON, J. (2021). Putative poison gland in the thorny catfish Acanthodoras spinosissimus (Siluriformes: Doradidae). Acta Amazonica, 51, 250-254.

https://doi.org/10.1590/1809-4392202101350
https://www.scielo.br/j/aa/a/kqCpDwFRdmJg78KPDGsLvwy/
ABSTRACT
Acanthodoras is the only genus of catfish known to secrete a conspicuous and abundant milky-looking substance through an axillary pore located just below the base of the posterior cleithral process. Despite this remarkable feature, there is no published information on the anatomical structures that produce the secretion and its possible biological/ecological functions. Dissection and histological analysis of preserved specimens of A. spinosissimus revealed the presence of a saccular axillary gland with large, binuclear secretory cells, similar to those found in other poisonous catfish. Secretory cells near the lumen appear to lose nuclei and become filled with secretory products, possibly with proteinaceous elements, as indicated by their eosinophilic appearance. As far as we know, the saccular morphology of the gland appears to constitute a unique characteristic of Acanthodoras among Doradidae catfishes. Further studies are necessary to determine the chemical composition of the secretion, as well as its possible uses by the catfish in its natural environment.
KEYWORDS: Amazon basin; defense; venom gland; freshwater
RESUMO
Acanthodoras é o único gênero de bagre conhecido por secretar uma substância de aparência leitosa conspícua e abundante através de um poro axilar localizado logo abaixo da base do processo cleitral posterior. Apesar dessa característica marcante, não há informações publicadas sobre as estruturas anatômicas que produzem a secreção, nem sobre suas possíveis funções biológicas/ecológicas. A dissecção e análise histológica de espécimes preservados de A. spinosissimus revelaram a presença de uma glândula axilar sacular com células secretoras binucleares, semelhantes às encontradas em outros bagres venenosos. As células secretoras próximas ao lúmen parecem perder os núcleos e são preenchidas com produtos secretores, possivelmente com elementos proteicos, conforme indicado por sua aparência eosinofílica. Até onde sabemos, a morfologia sacular da glândula parece constituir uma característica única de Acanthodoras entre os bagres Doradidae. Mais estudos são necessários para determinar a composição química da secreção, bem como seus possíveis usos pelo bagre em seu ambiente natural.
PALAVRAS-CHAVE: Bacia Amazônica; defesa; glândula de veneno; água doce
Attachments
Figure 1   A - Acanthodoras spinosissimus secreting the milky putative poison (arrows); B - Axillary pore (rectangle) of A. spinosissimus, located below the postcleithral process (pp), near the base of the pectoral fin (pf). C - Opened pore (rectangle); D - Axillary gland of a specimen of A. spinosissimus of 90 mm standard length, indicating the position of the axillary pore. pp = postcleithral process; pf = pectoral fin; ag = axillary gland; ap = axillary pore. This figure is in color in the electronic version.
Figure 1 A - Acanthodoras spinosissimus secreting the milky putative poison (arrows); B - Axillary pore (rectangle) of A. spinosissimus, located below the postcleithral process (pp), near the base of the pectoral fin (pf). C - Opened pore (rectangle); D - Axillary gland of a specimen of A. spinosissimus of 90 mm standard length, indicating the position of the axillary pore. pp = postcleithral process; pf = pectoral fin; ag = axillary gland; ap = axillary pore. This figure is in color in the electronic version.
Figure 2   Histological aspects of the axillary gland of Acanthodoras spinosissimus. A - Longitudinal section of the gland; B - Binucleated secretory cells; C - Secretory cell filled with secretory product. sh = gland sheath; lo = lobule; lu = lumen; sc = secretory cell. Staining with Hematoxylin-Eosin. This figure is in color in the electronic version.
Figure 2 Histological aspects of the axillary gland of Acanthodoras spinosissimus. A - Longitudinal section of the gland; B - Binucleated secretory cells; C - Secretory cell filled with secretory product. sh = gland sheath; lo = lobule; lu = lumen; sc = secretory cell. Staining with Hematoxylin-Eosin. This figure is in color in the electronic version.
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