I think that Helen has brought up the beginnings of a very good point when she mentions the barbels of catfish. If the immune system of an animal is compromised because of poor living conditions, then bacteria will take advantage. I have not seen any studies on the amounts or types of bacteria that live in the substrate of either regularly cleaned or neglected aquaria, however, it would be logical to consider that a very high bacterial load would and could result in overwhelming challenges to a potential host immune system. Even generally non-pathogenic bacteria could produce a very high concentration of metabolic waste in the immediate environment of wrigglers of substrate spawning fish. The resulting 'chemical poisoning' would compromise the immunity of these tiny creatures making them susceptible to a breach of their external membranes, infection and then death. Larger fish, because of their more mature immune systems with antibodies caused by various exposures during their life time, would not succumb as easily as their fry. Furthermore, they don't have to remain so close to the substrate, catfish being a good example of a fish that must root through the substrate in their search for food and thus suffering because of infection of their barbels. G. Kadar Helen Burns wrote: >Surely to avoid any build up of substrate bacteria is by carrying out >regular gravel cleaning. Yes it is much colder over here (Scotland) and all >tanks have heaters unless the fish house is space heated, even then many >tanks have individual heaters. Water current is essential to circulate the >heat within the tank. When a spawn hatches the wrigglers are moved and >cleaned by the mother several times each day before they are free swimming. >Some catfish owners wonder why the barbels of their corydoras have >disappeared, simple answer - bacteria in the substrate - solution, regular >gravel cleaning. >Helen > ------------------------------------------------------------------------- This is the apistogramma mailing list, apisto@listbox.com. For instructions on how to subscribe or unsubscribe or get help, email apisto-request@listbox.com. Search http://altavista.digital.com for "Apistogramma Mailing List Archives"!