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Banded Darter eating algae?

Started by Guest_mangoverde_* , Nov 30 2012 03:16 PM

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7 replies to this topic

#1 Guest_mangoverde_*

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Posted 30 November 2012 - 03:16 PM

Last week a friend of mine brought home a few rocks and a stick covered in filamentous algae. He indicated that a few minutes after putting them into his tank one of his Banded Darters appeared to be eating the algae. He sent me a video but it was hard to tell if it was actually eating the algae. I had a lot of a darker colored filamentous algae in my tank which a stoneroller has plowed through but I never saw my Banded interact with it.

When out yesterday (Little Miami River, Hamilton County, Ohio) I brought home two rocks (total area similar to a saucer sized plate) covered in the same algae that my friend had brought home. Within minutes it was drawing attention from Orangethroat Darters (like to lay in it) and Southern Red Belly Dace (some light grazing). After about 30 minutes my Banded took over and did appear to be eating it, however I could not tell for sure. I took some video of the action. You can see it appear to munch on something which I assume is the algae. There were no obvious larvae mixed in with the algae but I imagine there was critters smaller than what I can see.

Today the algae is almost entirely gone. I am guessing the stoneroller hit it pretty hard during the night. The Banded and a male Greenside Darter are still trying to rest in what remains.

Does anyone think the Banded is feeding on the algae in the video? Has anyone seen one of their Bandeds feeding on algae?

Edited by mangoverde, 30 November 2012 - 03:17 PM.

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#2 Guest_Usil_*

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Posted 30 November 2012 - 03:32 PM

I have seen rocks like this in riffles and the algae comes and goes during the year, some times flowing wildly and other times barely visible. Also, perfect habitat for darters which I also see in the same riffles. I think they just see something normal to their environment. Although, I have not observed them eating the algae they live on the bottom so it might be an opportune meal from time to time or they just might be going after the water animals they see flicking or crawling by that are living in the algae.

Usil

Edited by Usil, 30 November 2012 - 03:34 PM.

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#3 Michael Wolfe

Board of Directors

North Georgia, Oconee River Drainage

Posted 30 November 2012 - 04:18 PM

Looks to me like he is "striking" at something with a quick motion... like he would if he saw a little critter down in there... you dont need to sneak up on a plant, ot strike at it quickly, its not moving... that behaviour looks like the micro-predator that darters really are. Now that one time he hits pretty hard and there is a little tuft of sand fly up even and he probably dislodged some algae... maybe even took a little in with teh bug he was hunting... but I see a hunter hunting, not a grazer grazing.

Either write something worth reading or do something worth writing. - Benjamin Franklin

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#4 Guest_EricaWieser_*

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Posted 30 November 2012 - 06:56 PM

One way to test this is to get another of those rocks and stick it in a brine bath for a few minutes before rinsing it off and putting it in their tank. The salt water will make whatever little bugs are on the algae let go and float up into the brine water. When it goes in their tank it'll be just algae, no little animals. If they still eat it then, they're eating the algae.

I wouldn't be surprised if they were eating the algae. Very few predators eat only 100% meat. My cat eats grass. Some predatory fish need plants in their diet, too.

Edited by EricaWieser, 30 November 2012 - 06:57 PM.

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#5 Guest_Ken_*

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Posted 30 November 2012 - 10:58 PM

I agree with Michael. Preditory fish get their plant nutrients from plant material comsumed by their prey. Their are omnivirous fish but I have yet to see a darter that is.

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#6 Guest_MichiJim_*

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Posted 01 December 2012 - 11:58 AM

I agree with Michael and Ken. The video shows hunting behavior, not grazing. The algae gets disturbed by this activity, and some gets consumed by the darter while pursuing its prey. Its similar to what happens along a floodplain in the winter. Small critters eat the slime the grows on the dead leaves from the previous fall and break down the leaves in the process. Come spring, the floods clean it all up and a new cycle begins. I had a professor that refered to this as the peanut butter cracker theory. The objective is to eat the peanut butter, but the cracker gets eaten along with it. Not a perfect metaphor, and a more complex ecological process than outlined above, but it works.

The relationships between seamingly unrelated actions by the variety of life in and around a stream is what keeps me coming back to the wild. And speaks to the importance of biodiversity, including the relationships we may never really see.

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#7 Guest_EricaWieser_*

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Posted 01 December 2012 - 02:56 PM

The predators who hunt microprey and who are purely carnivorous, like Elassoma zonatum, only ingest minute amounts of algae.

Stomach contents of 46 individual banded pygmy sunfish (26 of which were spawning adults) collected at Mound, Louisiana were examined for food identification by Barney and Anson. The main food identified at Mound included insect larvae (mostly from the family Chironomidae), small crustaceans and snail eggs. The crustaceans and snail eggs combined constituted the majority of the content. Next in quantity was the insect larva. It is also noted that minute amounts of algal spores were ingested by these fish. It is most likely that these algal blooms were taken in accidentally with other prey. Lastly, no other fish species or banded pygmy sunfish larva were found in the stomach contents.

Barney, R. L., and Anson, B. J. 1920. Life History and Ecology of the Pygmy Sunfish, Elassoma Zonatum. Ecology 1:241-256.
via wikipedia

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#8 Guest_mangoverde_*

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Posted 03 December 2012 - 03:31 PM

Looks to me like he is "striking" at something with a quick motion... like he would if he saw a little critter down in there... you dont need to sneak up on a plant, ot strike at it quickly, its not moving... that behaviour looks like the micro-predator that darters really are. Now that one time he hits pretty hard and there is a little tuft of sand fly up even and he probably dislodged some algae... maybe even took a little in with teh bug he was hunting... but I see a hunter hunting, not a grazer grazing.

That was my thought when my friend sent me his video. I thought it was predator/prey behavior. Then, when I watched it in my tank with algae that I looked through to see if I could find any critters (I was actually out catching live food for my darters when I brought home the algae covered rocks) I was not so sure. In some parts of the video it stays in generally the same place and "strikes" forward or down to grab something, either algae or a very small critter without any apparent searching prior to the strike. I observed this behavior outside of the video as well. At other times it does appear to look down first. If it is eating algae, which I have not confirmed, it may be that what appears to be a strike mechanism is its way of tearing some free given that it may not have a mouth built for grazing. Stonerollers and dace, in my tank, use different approaches to eating algae. The stoneroller is more a of scraper/grazer while the dace swim up tear a piece free and then swim away.

I agree with Michael. Preditory fish get their plant nutrients from plant material comsumed by their prey. Their are omnivirous fish but I have yet to see a darter that is.

At times I will put small amounts of nori (toasted "seaweed", in this case Porphyra tenera) in my tank for the dace. My Orangethroat Darters will eat it. I have seen the Banded Darter take large pieces in its mouth and then spit them out. My two Greenside Darters become active when I put the nori in but I have not observed them trying any. Some of the Rainbow Darters will come out of their rock piles, probably to see what the excitement is about, but quickly bunker down again. Fantails and Slenderhead how zero interest. The Orangethroats, however, are definitely eating it.

I agree with Michael and Ken. The video shows hunting behavior, not grazing. The algae gets disturbed by this activity, and some gets consumed by the darter while pursuing its prey. Its similar to what happens along a floodplain in the winter. Small critters eat the slime the grows on the dead leaves from the previous fall and break down the leaves in the process. Come spring, the floods clean it all up and a new cycle begins. I had a professor that refered to this as the peanut butter cracker theory. The objective is to eat the peanut butter, but the cracker gets eaten along with it. Not a perfect metaphor, and a more complex ecological process than outlined above, but it works.

The relationships between seamingly unrelated actions by the variety of life in and around a stream is what keeps me coming back to the wild. And speaks to the importance of biodiversity, including the relationships we may never really see.

To me, the initial part of the video does not appear to show typical hunting behavior although it may just be a pattern I have not previously observed. It seems like it is in the same general spot while striking forward or down while adjusting for the current. Towards the end it does appear to look down before the strike that releases the big cloud of sediment. Another interesting thing is that it appears to be chewing after the strike. With prey that would have been too small for me to see, I think this must mean that either it is chewing the incidental algae that you suggest or it is chewing up a bite of algae. I have watched it take in visible midge larvae whole with no chewing involved. It may be that it is the peanut butter analogy and that it does not even need to look for small critters. Maybe it assumes they are there and the algae is the delivery agent. Or, maybe it is deliberately eating the algae just for the algae.

Thank you everyone for the replies and interesting dialogue. I am definitely going to repeat the experiment and few more times and get more video. I will probably try the brine bath as Erica suggested as well. The one paper I found online that had a dietary analysis of zonale did not mention any vegetable matter.