Larval blind cave fish retain pineal eye Practical Fishkeeping
Researchers at the University of Maryland have found that larval blind cavefish (Astyanax mexicanus) retain a functioning pineal eye that is capable of detecting light.
In the study published by Masato Yoshizawa and William Jeffery in the most recent issue of the Journal of Experimental Biology, the authors studied the response of larval cavefish reared from eggs kept in total darkness to the shading of light.
The researchers have the function of the "pineal eye" backwards. "The cave systems inhabited by Astyanax cavefish can contain karst `windows', areas of ceiling collapse that allow dim light penetration, and are subject to periodic episodes of extensive flooding...Floods could propel cavefish from the light-less cave interior to semi-lighted locations, such as near cave entrances or spring resurgences. Both scenarios could expose cavefish larvae to predation in lighted habitats. Conservation of the pineal eye could be used to avoid the potential threat of exposure to light and predation.”
The use of such subtle light detection equipment in karst window environments would allow the larvae to find plentiful *FOOD*! washed in from outside. Duh.
Anecdotal evidence: a cavefish containing always shaded karst window in Southern Missouri contains one of the largest populations of one species of cavefish in the state per meter. (Another cave has more fish, but it is much much bigger). Nearly all of these cavefish are OUTSIDE in the shadow zone or near the surface of the connected underground lake. Dives to depth in the lake (over 50 meters) by fish counters indicate that well in excess of 90% of the fish are either outside or in the top shallows. Why? Are they masochistic fish? No.
They are hungry, and that is where the food is. I don't dive, but have the dive data. I've seen the karst window fish: they are happy, active and sassy compared with most fish who live in the caves. I do wonder in the case of springs, if the fish come out and feed at night?
Post by Brian Roebuck on Jan 24, 2008 6:46:50 GMT -5
It makes sense that cave fish would travel to any viable food source where it is safe enough to feed. Blind fish would be able to sense the absence of predators in night time springs if they were able to get to them. With food being so scarce they certainly would give it a try if they could!
Brian Roebuck NSS 34626 RL (FE) ----- Caving is far too serious to be taken seriously.
Trout, and other larger river fish (One reason springs with cavefish in the passages do not have cavefish in the pools. Of course, a sunburn will fry them, too. It's the UV and infrared on internal organs which get them, not the visible spectrum so much.)
Raccoons. (Believe it, or not. In the late 1960s, Fantastic Caverns in Springfield, Mo. had a couple of cavefish in a shallow pond on the visitor level (usually the fish are in the lower level stream). These fish would be shown off to some visitors. My friend Don mapped the cave in return for room and board during his college years. He reported that one day, the fish were there, and the next day, the fish were gone, but raccoon tracks were present. Yum. )
Salamanders eat cavefish larvae and vice versa, depending on size.
I'm speculating on the cavefish coming out at night because there is no sun, and that's when sculpin abound. But it likely would have to be pond situation, or the cavefish could never retreat. Many of them travel only a few hundred feet in their lives from tagged surveys, unless they are forcibly swept out by storms.