Two More Odd Things I Just Learned About Fish

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When I'm not blogging for mental_floss, I can usually be found wearing bright orange rubber pants and gutting, cutting and selling fish at my local Whole Foods (and winning awards for it). Sometimes, my two worlds collide and I find some scientific research involving my ocean-dwelling friends that begs for a blog post. This is one of those times.

1. Dying Zebrafish Give Their Kids a Powerup
Many animals give off biochemical signals when they're frightened or hurt to warn other members of the species of danger and elicit anti-predator and defensive behavior. The effects of these "alarm substances" on juvenile and adult animals have been the subject of many studies, but researchers at the Marine Biology and Ecology Research Center at the University of Plymouth wanted to know how embryos still in the early stages of development would respond to the substances. [1]

Embryos of two species (Danio albolineatus and D. rerio) of zebrafish, tropical freshwater members of the minnow family native to southeastern Himalayan region, were exposed to skin injury-induced alarm substances from adults of the species and filmed during development. The development time of both species was sped up, and alarm substance-exposed embryos reached their first muscular contractions (D. rerio) and their first heartbeats (D. rerio and D. albolineatus) earlier than control embryos.

The exposure to the alarm substance caused the embryos to developed a functional heartbeat almost 10%, or 1.5 to 2 hours, faster than normal. That might seem like a snail's pace to us, but after fertilization, zebrafish develop precursors to all the major organs within 36 hours, hatch within 48 hours and begin swimming and feeding within 72 hours. Speeding up development by even just an hour reduces the time the embryos are vulnerable in their egg case and possibly not under the guard of their parents.

How will these developmental advances affect the fish later in life? The researchers think they could either be a sign of an increased development rate overall (with the fish rushing through all their developmental stages), or they could relate to later physiological or behavioral traits.

2. Stingrays Are Smarter Than They Look
rayFreshwater stingrays, the tropical river-dwelling relatives of ocean-going stingrays, have, like sharks and other cartilaginous fish, long been thought of as reflexive machines without cognitive capacity and ability (in part because they're difficult to study). Well, we owe them an apology, because they recently joined a very special club: the royal order of animals that use tools.

In an experiment, researchers from the Hebrew University of Jerusalem in Israel designed a plastic tube test apparatus with two openings and placed a piece of food in it.[2] All five of their stingray subjects (Potamotrygon castexi) figured out how to get the food out of the tube with a carefully directed jet of water (which meets the basic definition of a tool), the first indication of tool use in the batoid fishes. That's one small step for understanding the evolutionary origins of cognitive function in higher vertebrates and one giant leap for raykind. Congrats, guys.

[1] S. Mourabit, S. D. Rundle, J. I. Spicer and K. A. Sloman. "Alarm substance from adult zebrafish alters early embryonic development in offspring." Biology Letters. DOI:10.1098/rsbl.2009.0944

[2] M. J. Kuba, R. A. Byrne and G. M. Burghardt."A new method for studying problem solving and tool use in stingrays." Animal Cognition. DOI: 10.1007/s10071-009-0301-5

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February 23, 2010 - 9:10am
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