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Blind Cave Fish: Their Discovery, Initial Collection and Care – Part 2

April 25, 2008 5 Comments 7597 Views

Blind Cave Fish

Click here to read the first part of Blind Cave Fish
Blind cave fish navigate entirely through the use of the lateral line – a system of sensory organs possessed by all fish but, it seems, very highly developed in this species. The movement of water (caused by currents or the fishes’ own swimming) bouncing off objects is sensed and used to guide the fish in their travels. I am tempted to compare the process to echo-location in bats, or the use of electricity by the elephant nose fish, Gnathonemus petersi, but it is, of course, quite distinct. If you have an opportunity, observe how well cave fish can move about – in an exhibit at the NY Aquarium they speed through a series of glass barriers unerringly. Individuals introduced to new exhibits may “crash” on occasion, so there may be some learning involved as well.

They are also amazingly adept at locating food – a school I kept at the Prospect Park Zoo in NYC hit food dropped on the water’s surface as quickly as do most sighted fish. In fact, blind cave fish do quite well in aquariums housing other fish species.

Recently (January, 2008) it was discovered that young blind cave fish can detect light via unique compounds in the brain’s pineal gland (the embryos begin to develop eyes, but these degenerate rapidly). This ability declines with age.

In contrast to most cave-adapted fish – which require cold, hard water if they are to thrive – blind cave fish are quite undemanding pets. In fact, they do best at 78-82 F, as their native waters are quite warm. If kept alone, slightly hard water should be provided, but they adapt easily to conditions suited to most community-type tropical fish. Despite a very specific natural diet (see above), blind cave fish remain healthy on almost any commercial fish food – I have successfully used a mix of omnivore flakes and pellets, along with frozen foods. They ravenously devour black worms, brine shrimp and such, and are especially fond of crushed crickets and other insects. Their reaction to insect food brings, at least to my mind, an image of feeding behavior in their native cave. At feeding time, they compete quite well with other fish and rarely require special attention.

Blind cave fish are placed within the order Charachiformes, an extremely diverse group of fishes containing well over 1,500 species, including tetras and the infamous piranha. I will write about piranhas in a future article, and will include photos of some that became “attached” to me while I was seining for knife fish in northern South America. Until then, please forward your comments and questions. Thank you. Until next time, Frank.

A fascinating account of the first expedition to collect blind cave fishes, including original drawings and photos, is given in Zoo Expeditions, by William Bridges (William Morrow & Co., 1945). Long out of print, this book is well worth searching for.

An interesting article on the evolution of eye regression in this fish is posted at:
http://findarticles.com/p/articles/mi_qa3746/is_199809/ai_n8816250

Thanks Frank,

Until Next Time,
Dave

Blind Cave Fish: Their Discovery, Initial Collection and Care – Part 1

April 24, 2008 3 Comments 4983 Views

Blind Cave Fish

Please welcome back Frank Indiviglio for another fascinating species profile.
Perhaps because of its lack of color, the blind cave fish, Astyanax fasciatus mexicanus, does not receive nearly the attention it warrants. This 5 inch-long fish was first discovered by Salvador Coronado, a young employee of Mexico’s Department of Fisheries, and it was he who later led a New York Aquarium sponsored expedition to collect the bizarre creatures. The species’ entry into the aquarium world’s consciousness is recounted by expedition member William Bridges, of the Bronx Zoo, in his initial report – “…at three o’clock on a March afternoon, a thousand feet inside the cave, two of us dragged a net out of the black water and revealed a dozen little flopping white fish…”. Amazingly, fish from that first collection appeared in three distinct forms – with normal eyes, with eyes of reduced size and without eyes. Fortunately for we fish enthusiasts, captive-born blind cave fish eventually found their way into the pet trade.

The blind cave fish is found in only one cave, La Cueva Chica (the “Little Cave” – the entrance is only 15 feet wide) near Pujal, in San Lois Potosi, Mexico (related species have since been found in other caves). This fact alone should grant it special status among fish keepers, but there is much more to distinguish it – including a rare glimpse at fish adaptation in progress. Apparently, fish with normally developed eyes live in a nearby river, the Rio Tampaon, and are regularly swept into the cave by the current. There, deprived of light and the need for sight, the eyes degenerate. As time goes on, their descendents are born with gradually more reduced eyes, until the eyeless form emerges. Although I have not read evidence of it, I imagine that inter-breeding with eyeless fish already in the cave may hasten the process.

Fish in pools nearest the cave’s entrance rely upon flies, spiders and other invertebrates for food, while those deep inside subsist upon bat guano, dead bats and, I would venture a guess, fleas and other invertebrates that fall from the bats’ fur.

Check back on Friday to read the rest of this article.
Until Than,
Dave