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Name: Dale
Status: Student
Age: 19
Location: N/A
Country: N/A
Date: N/A 

I read that certain deep sea fishes have spots of bioluminescence directly under their eye, this made possible by a colony of luminescent bacteria living there.

How do the bacteria manage to get into this spot in every fish? Or are there just some fish with this spot and some without, without actual regard as to which species it is but rather just which fish was lucky enough to meet up with some bacteria?

Hi Dale,

You are right, 'always' and 'never' are very strong concepts in biology, however host-specificity in bacteria can be very definite. It is best described for bacterial pathogens that colonize some hosts but not others, and cause disease in some (or all) of the hosts they colonize. Commensals and symbionts also display host-specificity, dictated by adhesin-receptor interactions, and less well-defined mechanisms. In the case of luminous bacteria in fish light organs, my guess is that this is a specific interaction, where only certain fish species 'allow' the presence of only certain types of bacteria. In this particular case it even seems gender specific. I couldn't find literature that described the mechanism behind it, but you can guess this may be hormone-dependent (do male fishes produce a light-organ all together?), or receptor specific.

In conclusion, the interaction of these fish and their bacteria is probably specific. The way these bacteria find their right host may be by chance. It is likely that both bacteria and host profit from the situation.

Trudy Wassenaar

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