#minnows

There are four types of fish scales!

One of my absolute favorite native fish species is the longnose dace (Rhinichthys cataractae). A weird minnow specialized for life in the most fast-flowing torrents of rocky rivers and streams, they use their funny snout to grub in the gravel for small invertebrates, algae and any edible detritus. They have perhaps the largest native distribution of any North American freshwater fish, found coast to coast across much of the northern US and most of Canada.

If you’ve ever been bitten by blackflies (Simuliidae), I hope you’ll be pleased to know that longnose dace are one of their main predators! Blackfly larvae cling to rocks in swift waters where few fish can brave the current but longnose dace feel right at home. Blackfly larvae make up a large proportion of their diet, so without the dace there would be a lot more blackflies around.

Happy Tuesday, everybody! Today's fish of the day is the Devils river minnow!

The Devils river minnow, also known by scientific name Dionda diaboli, is a rarely found fish. Found in only three remaining locations across Texas and Mexico. Particularly: Val verde, and Kinney counties, Tx, and Coahuila, Mexico, throughout the Chihuahuan desert. Their habitat is found in areas across the Devils river, or Rio Grande meets spring waters, in the ecological transition zone. Clear, slow moving waters with little pollution, and fine gravel bottoms, through temperatures of 15° C to 31° C. As these areas are known for extreme drought conditions, as well as flash flooding, the devils river minnow may withstand fast waters during strife. It is believed their range used to be much larger, however it has been fragmented by extreme pollution, as well as extensive dam building throughout the rivers.  

The diet of these fish is lightly debated, as no one has seen them eat in the wild. However the shape of their gut, and stomach contents imply these fish feed near exclusively on algaes, and other vegetation. In captivity, they'll feed on brine shrimp as well, implying there may be zooplankton in their diet in the wild. Adult fish will gorw only 1-2 inches in length, making them easy prey. Particularly, to the invasive smallmouth bass, which is thought to be the reason the species, and similar species in the genus, have had dramatic decreases in population. These minnows can be visually found by the distinctive wedge shaped spot near the tail, as well the dark markings on the dorsal side, appearing as though they have a cross hatching pattern. 

Little is known about the reproduction of the Devils river minnow, but they're known from spawning from January through August. This long spawning season allows these fish the ability to have multiple batches of babies per season. These fish are visually distinct in spawning forms, female fish will remain their average colors, but male fish have tubercles across the head and pectoral fins. They're broadcast spawners, meaning they release eggs and milt to connect externally, once fertilized the eggs will fall to the bottom and incubate in the substrate for weeks to months. Once hatched, these fish will then mature quickly, ready to breed within a year, if they survive that is. beyond this. We know little of their life cycle, beyond that they live only 1-2 years. 

One of my inner mantras when I’m out in nature is this: if something is worth a look, it’s worth a close look. So when I stopped to look over a railing at this nondescript corner of a pond, I forced myself to pause and spend some extra time looking closer at the scene at hand. Aside from the larger fish swimming below (which I am regrettably unable to ID) I greatly enjoyed watching the little “minnows” just under the surface. These fish are lively and entertaining to observe as they forage for food and squabble with one another, but they’re often overlooked by even the most ardent wildlife enthusiasts here. I grew up catching and observing minnows for fun and I’ve got a real soft spot for them, so here’s a little deep dive into these shallow water fish!

While a big school of minnows may not look like much at first blush, hardly anyone could deny the beauty of a Sailfin Molly after they’ve had a proper look at the fish.

If you’re trying to spot this species in a group like this, look for the blue tail and orange head of a mature male (quick mnemonic- red head= Molly like Molly Ringwald) but remember there can be a ton of color variation in mollies. These fish are feisty and bold; you’ll often see them chasing other mollies to defend their territory. If you watch closely enough you might get to see a male flare his oversized dorsal fin in a courtship display that is quite impressive.

Perhaps less visually striking but no less interesting in behavior is this little fellow, the eastern mosquitofish.

The Eastern mosquitofish is considered an invasive species in many places where it has been introduced by human activity, but here in their native home you can’t help but love em. The species is so named for their favorite prey (water borne mosquito larvae) and you can imagine how this particular behavior would be appreciated by us mammals that live near water! Mosquitofish (like the sailfin molly) often inhabit water that is lower in oxygen concentration, and have thus evolved an upturned jaw that allows them to take in water closer to the surface where it is richer in oxygen. It also happens to give them an adorably tough little expression for such a tiny fish.

While observing this group I got a special treat and spotted an Eastern mosquitofish with a genetic mutation!

This is a melanistic male, which is a mutation that is fairly well documented in my area. Although you might think that males with this mutation would be more susceptible to predators due to their flashy appearance, there is some research suggesting these melanistic males are actually targeted by predators a bit less than wild-type males. There is also at least one study showing that some females of the species prefer the look of these handsome black-and-white males, making it more likely to be passed down than other mutations might be. When I was a kid we called these “Salt-and-pepper” minnows.