Are club cells, fright cells?

Many the scaleless fishes have numerous large eosinophilic cells in their epithelium called “club cells”. In the old days, they were often labelled as “fright cells”. The reason for this name is that it was thought that when fish are stressed or being attacked, these cells are activated to release chemicals that will warn their conspecifics of danger and to avoid the area. “Recent studies demonstrated that predation has no effect on club cell investment. Rather, club cells have an immune function and cell production may be stimulated by skin-penetrating pathogens and parasites.” Check out this article for more detailed information.

Journal of Fish Diseases
Volume 35, Number 4 (April 2012)
	Do fathead minnows, Pimephales promelasRafinesque, alter their club cell investment in responses to variable risk of infection from Saprolegnia?
	Authors:	R J Pollock 1, M S Pollock 1, M C O Ferrari1,2, S G W Kaminskyj 1, D P Chivers 1
	Author Affiliations:	1: Department of Biology, University of Saskatchewan, Saskatoon, SK, Canada 2: Department of Biomedical Sciences, WCVM, University of Saskatchewan, Saskatoon, SK, Canada
	Source:	Journal of Fish Diseases, Volume 35, Number 4 (April 2012)
	Page Numbers:	249 – 254
	Available Full Text:	Full Text: Subscription Required to view full text Format: PDF Size: unknown Location: Publisher’s Site Authentication: EBSCOhost EJS
	Abstract:	Fish in the Superorder Ostariophysi possess large epidermal club cells that release chemical cues warning nearby conspecifics of danger. Despite the long-held assumption that such club cells evolved under the selective force of predation, recent studies demonstrated that predation has no effect on club cell investment. Rather, club cells have an immune function and cell production may be stimulated by skin-penetrating pathogens and parasites. The current work investigates whether fathead minnows, Pimephales promelas, alter their club cell characteristics based on variation in infection risk. In a 2 × 3 design, we exposed minnows to infective cysts of two oomycete species (Saprolegnia feraxand S. parasitica) at three different concentrations (2, 20 or 200 cysts L-1). Club cell characteristics (number and size) were quantified 12 days after exposure. Saprolegnia parasiticais thought to be more pathogenic than S. ferax, hence we predicted greater club cell investment and a larger turnover rate of cells by minnows exposed to S. parasiticathan S. ferax.We also predicted that minnows exposed to higher numbers of cysts should invest more in club cells and have a higher turnover rate of cells. We found no difference in club cell density or size between fish exposed to the two Saprolegniaspecies; however, fish exposed to high concentrations of pathogens had smaller club cells than those exposed to low concentrations, indicating a higher rate of turnover of cells in the epidermis.
	Citation:	R J Pollock, M S Pollock, M C O Ferrari, S G W Kaminskyj, D P Chivers . Do fathead minnows, Pimephales promelasRafinesque, alter their club cell investment in responses to variable risk of infection from Saprolegnia?. Journal of Fish Diseases, Volume 35, Number 4 (April 2012), pp. 249-254, <http://ejournals.ebsco.com/direct.asp?ArticleID=476E9906787317EDC908&gt;
	URL:	http://ejournals.ebsco.com/direct.asp?ArticleID=476E9906787317EDC908