Thursday, June 19, 2014

Video of a massive mountain redbelly dace congregation

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Occasionally when we are out in the field, we are fortunate enough to run across unusual or unexpected animals, or even better if you're far enough out there and get really lucky, you can witness unusually large groups of animals displaying natural behaviors and paying you no heed. In this case, a large shoal or "school" of nuptial mountain redbelly dace - with some rosyside dace, crescent shiners, and even a crayfish in there - have gathered on a chub nest to mate and are on full display. The beauty of these fish is hard to rival and create a living mosaic of red, gold, yellow, olive, black, white and silver.

Thursday, June 12, 2014

Mating season! Male redline darters fight it out, gilt darters mate, greensides mate

A large dominant male gilt darter in breeding colors

Late spring is breeding season for the majority of Virginia freshwater fishes; depending upon water temperatures, most darter species breed somewhere between early April to late May. Prior to (potential) spawning, male darters develop more intense coloration and exaggerated patterning than their normal appearance to outdo their male rivals in the hopes of attracting a female.
Male redline darter on display

Mature males will often spar with one another over territory or a single female, nipping at each others's fins and tails (see video below) often violently. Theoretically the dominant male wins out, but often the female pays either off them little notice and casually swims away as the males are still fighting. 
video
Two male redline darters fight over a female

Once a couple has paired off, they typically engage is some sort of courtship behavior that signals the beginning of actual mating. Many darter species show similar courtship and mating behaviors; for example the males of Genus Percina and many Etheostoma species as well swim alongside the female often weaving along her body from side to side, then when she settles into a good spot (presumably for laying eggs) he hovers over her and quivers his entire body so fast its a blur. Both videos below show this behavior from two species of each respective Genus. 
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Two gilt darters mate while a stoneroller watches and then rudely interupts

video
Two greenside darters mate and then also get rudely interrupted by a stoneroller

As seen in both video, these behaviors - at least in our stream exhibit - also trigger a feeding response in the other fishes looking for an easy meal of freshly lain eggs...or they are just excited by the activity. In either our exhibit or in the wild, successfully fertilized eggs face very long odds to reach maturity, but that's the reason these spawning events are so critical. They must find the right mate with good genes, create enough fertilized eggs to account for all the natural mortality, and spawn at a time when their young will have maximum food available as they grow. Because after their little spawning dance, mom and dad have done all they are ever going to do for their offspring.