Pond Boss Forums INTRO Questions & Observations BG eating vegetation

I was watching Bill Dance's fishing show yesterday and in just a little 10 second tip he mentioned that Blue Gill switch to eating vegetation at some point during the year. He didn't explain why. IIRC (which is doubtful) I think that he said that they switched to eating vegetation in late summer or fall. In the show his point was that during this period they would be harder to catch.

In all my many, many years on Pond Boss and even though I have been ever so studious I don't recall anyone ever mentioning that Blue Gill switch into a vegetarian mode at some point during the year. Seems kinda suspect to me.

What say you?

It depends. For example small BG eat plankton which are plants. BG eat bryozoans which in visible form are more like plants. BG do eat some plant matter depending on location and availability of other sources. It depends also on time as food source availability comes and goes during the year (bug hatch , prey fish spawn , etc)

There's a fellow on my OTHER FORUM who is a fisheries biologist, when someone posed a question about BG diet and whether or not they eat vegetables (aquatic plants/algae), here was his response:

drstressor from fishsniffer forum:
"Blue gills are very opportunistic feeders. But like any fish, they key on the most abundant type of prey. In your little pond, that would be invertebrates that live in the benthic detritus (the green scum that grows on the bottom and sides of the pond). While they ingest plant material, they are really living off the insects larvae and zooplankton that live in the green stuff. Blood midge larvae typically make up most of the diet of wild benthic feeding blue gills. You probably have them in you pond. They spin little green tubes attached to the bottom and walls.

If you don't feed your fish regularly, it will not respond very well to food put into the pond. Its brain associates food with things living down in the benthos. You would have to teach it to take live prey or pellets. Wild blue gills see a much wider selection of prey and the abundance of each type of prey varies through the season. So they will readily take baits that you fish would not recognize.

You can teach fish to feed on pretty much anything if you work at it. I had a Sacramento perch in a tank with a bunch of chubs for over 2 years. While the chubs would eat any fish food put into the tank (trout pellets, goldfish food, etc), the perch would only eat live prey. It would readily take live flies and brine shrimp. Since is was a PITA to get live food, we would only feed it maybe once or twice a week. So the perch never grew bigger than 2.5". Just before I retired, I gave the perch to another UNR faculty member who put it into a tank with some cichlids. He never gave it live food and after a period of weight loss, it figured out the pellet thing. It grew to 9" in 3 months, contaminated the water, and died taking the cichlids with it."

Is there a way that I can get permission to use this quote, and also to know who is the smart person that made it?

Bill Dance doesn't always know everything, I guess.

DIED see what you think after this. I do believe it depends on many factors as BG are generalist feeders.



Epiphytic Macroinvertebrates as a Food Resource for

Bluegills in Florida Lakes

HAROLD L. SCHRAMM, JR.,1 AND KURT J. JiRKA2

Department of Fisheries and Aquaculture, University of Florida

Gainesville, Florida 32606, USA

Abstract. — Biomass of aquatic macrophytes, densities of benthic and epiphytic macroinvertebrates,

and the food consumed by bluegills Lepomis macrochirus 75 mm in total length and longer

were quantified and compared in different macrophyte communities in February, April, June, and

August 1983 in two Florida lakes (referred to as community-date comparisons). Densities of

benthic macroinvertebrates ranged from 88 to 1,933 individuals/m2. Densities of epiphytic macroinvertebrates

ranged from 721 to 34,379 individuals above 1 m2 of bottom and were 30-99% of

the total macroinvertebrates in and above the bottom. The composition of the bluegill diet was

positively related (P s 0.05) to the epiphytic macroinvertebrate assemblages in 13 of the 15 possible

community-date comparisons but not related to the benthic macroinvertebrate assemblages in any

community-date comparisons. The greater similarity of the bluegill diets to the epiphytic than to

the benthic macroinvertebrate assemblages suggested that bluegills obtained most of their macroinvertebrate

prey in the vegetation and little from the benthos. Linear selectivity indices indicated

positive selection for chironomids, caddisflies, mayflies, odonates, hemipterans, and Palaemonetes

spp. Except for Palaemonetes spp., these taxa generally were more abundant among the epiphytic

than among the benthic assemblages. Because of the abundance of epiphytic macroinvertebrates

and their consumption by bluegills, management for macrophytes can enhance the prey resource

for adult bluegills.



The greater similarity of the bluegill diet to the

epiphytic than to the benthic macroinvertebrates

in 13 of 15 community-date samples suggests that

bluegills obtained more prey from the macrophytes

than from the sediments. However, because

epiphyton were more abundant than benthos,

and because epiphyton occurred in a more

extensive foraging area than did the benthos (i.e.,

epiphytic invertebrates could be encountered

throughout the water column, whereas benthic

ones could be encountered only at the sediment

surface), consumption of epiphytic prey could have

resulted from greater availability of epiphytic organisms

than of benthic ones. The greater similarity

of the diet to the epiphyton than to the total

macroinvertebrate assemblage suggests that bluegills

preferentially consumed epiphyton.



In agreement with other researchers Werner

and Hall 1976, 1979; Keast 1978; Mittelbach

1984), we concluded that bluegills fed predominantly

on epiphytic macroinvertebrates in Orange

and Henderson lakes. However, bluegill feeding

behavior can be influenced by competition from

sympatric fishes with similar food habits, by predators,

and by differential profitability of food resources.

In the presence of competitors feeding on

the epiphyton, bluegills decreased consumption of

epiphytic invertebrates and increased consumption

of benthic and planktonic invertebrates (Werner

and Hall 1976, 1979).



WINTER FEEDING HABITS OF BLUEGILLS, LEPOMIS MACROCHIRUS

RAFINESQUE, AND YELLOW PERCH, PERCA

FLAYESCENS (MITCHILL), IN CEDAR LAKE, WASHTENAW

COUNTY, MICHIGAN •

JAMES W. MOFFETT

AND

BURTON P. HUNT



FEEDING HABITS OF BLUEGILL

During the winter of 1940-41, bluegills in Cedar Lake consumed a

rather large variety of organisms although quantities taken were small.

Fifty-four genera were identified in the food eaten and this number is

minimal since several groups were identifiable to family only. In 1,128

sto•nachs examined (935 with contents, 193 empty) there was an average

of 133 organisms of which 124 were plankton. The average volumetric

content of these stomachs was 0.036 cubic centimeters including

debris.

Cladoeera (Daph•Ja and Bosmina) were the most numerous plankton

organisms eaten during early winter (Table 1). They beea•ne

subordinate to Ostracoda during midwinter and increased to a highly

dominant position in late winter. Copepoda were eaten consistently

but in relatively small numbers. Of the insect foods, mayfly nymph• .

belonging to the genus Blasturns were most abundant although Ephemerella

nymphs were almost as numerous. Together these genera made

the mayfly group more important than any other order of insects during

all periods when insect. foods were being'eaten in appreciable

numbers. At other times especially in midwinter the dipterous larva

Chironomus and Chaoborus, outnumbered them. Other insect components

were relatively unimportant and became increasingly so as the

winter progressed. The presence of Bryozoa in the winter diet of the

Cedar Lake bluegills is interesting. Wilson (1920) found Plumatella

ploymorpha in stomachs of bluegills taken from Lake Maxinkuckee in

late autumn.

Volumetric comparisons of the various components of bluegill diets

in winter are presented in Table 2. During the first 3 weeks of the

winter, mayfly nymphs, caddisfl y larvae, and dragonfly nymphs constituted

over 50 per cent of the volume of the food in the stomachs.

As winter progressed, plankton became increasingly important 'only

to decrease tb a relatively unimportant position by the time the ice

began to yield to spring weather. At no time did planktonic forms constitute

more than 54.6 per cent of the volume of the stomach contents.

Daphnia Were the predominant plankton group. Their volume was

less than that of Ostracoda during one week in midwinter but they

resumed their dominant position following that time. Mollusca were

eaten with the plankton, and during February were as volumihous as

that group, but in early and late winter their percentage in the total

diet was quite low. Mayfly nymphs, chiefly Blas'turus, were the dominant

insect group. They were exceeded in volume by Chironomus larvae

during 4 weeks in midwinter and by Trichoptera in the collection

of March 8-9. Mayfly nymphs again became the most important group

during the last week of the study when spring feeding, preparatory to

spawning, is presumed to have begun. There was a decrease in the

volume of insect life cons6med, Diptera excepted, during midwinter

and an increase as spring approached. I•Iowever, this trend was accompanied

by a general decreasein the average total volume per stomach

during midwinter and an increase toward spring (Fig. 1).

The feeding habits of bluegills change very little with the size of

the fish. Only when these fish approach a total length of 200 millimeters

(7.9 inches) do they tend to leave plankton and turn to feeding

on insects and fish. The percentage of total volume which each major

group of food. organisms constitutes in the diets of the various size

groups is presented in Table 3.

The food consumedb y bluegills in winter is very meager when compared

with the volumes eaten at other seasons of the year. Such restricted

feeding is believed to be a function of temperatures which control

the activities of the food organisms as well as the metabolic rate

of fishes. A comparison of the curve for the mean daily air temperature

with that for the average volume per stomach taken at each collection

date as shown in Figure 1, indicates a rough correlation between

extended periods of warmer weather and the consumption of food.

Usually, these warmer periods were acompanied by sunshine which,

presumably, warmed bottom deposits and shoal water where most

insect componentso f the bluegill diet were located. The rather large

volume of mayfly nymphs taken from stomachs collected February 15-

16 (Table 2), indicates a change in the feeding locale during this

warm period. Slight temperature rises of this sort might be sufficient

to increase the activity of food organisms and might also stimulate

the movements of fish. Such action would tend to account for the correlation

shown in Figure 1. This explanation is, of course, speculative

since data resulting from this study are insufficient to prove it conclusively

I find this fact very interesting.

Come on guys. Someone tell us the reasons for the differences in those 2 studies. They are simple and easy to note. Think about the nature of where the BG live for a clue as to why they have certain feeding behaviors.

Eric, I see exactly where you are going. I won't mess up the question.
Bluegill are opportunistic omnivores. (That is my hint for Eric's question)
Some of the observations I have made about bluegill may make a difference to this discussion. Back in the late 80's, I put a few bluegill in a 100 gallon aquarium and started feeding them a floating pellet that I used in ponds. They would eat it as it floated and they would attack it as it sank. But, once the food hit the bottom, they wouldn't touch it. So, just to test my theory, I soaked some of the floating pellets, mashed the air out of them and put them in the aquarium. The hungry fish ate the pellets as they sank, but when the pellets hit the bottom, bluegill didn't touch them. I decided to watch for similar behavior in ponds. I saw it, but not quite as dramatic as the aquarium. Some, but only a few, bluegill would pick up feed off the bottom of the pond. If they didn't get it off the top or on the way down, most bluegill ignored the food on the bottom. They rose back to the top, looking for more offerings.
Ever since those earlier days, I have observed bluegill feeding in the top few feet of a pond, but not below...as a whole. A few fish hit the bottom, but not many.
Take it from here, boys.

Can I participate? Although I am not as perceptive as Bob and I do not see where ewest is going?
There are several or probably numerous reasons for the differences between the feeding habits of BG in the two studies posted above by ewest; by the way ew, thanks for the good info you always provide for this forum.

1. Different water bodies. Lots of habitat varability can occur in two different water bodies. Habitat variability and food production of each different pond/lake alone can explain the differences.
2. Northern vs southern locations -obviously they can be quite different in the food items available
3. Different sized fish were used in the 2 studies. 1st study looked at 3" (75mm) BG vs 2nd study probably sampled or mostly used BG larger than 3"; although methods were not posted for us to see.
4. Different species and same species of fish present and their competitiveness toward BG or each other can account for some differences; assuming studies were not done in a monoculture of just BG.
5. It appears to me the studies were conducted during different seasons of year - 1st one no doubt during warm weather (Florida) possibly during summer when researcher was on break. 2nd one a winter in Michigan. Even B.Dance indicated BG feed differently in different seasons.

I have not read both studies completely so I cannot comment much more about specifics of each study.

IMO Bill Dance or whom ever or where ever he got his info, plus many others probably looked at stomach contents of some BG during late summer or fall when catching BG was difficult, in order to see what they were eating to "match the hatch". Contents no doubt looked like green plant matter. Several things could have contributed to this. One possibility is if small or thin "shelled" or very soft bodied bugs are consumed with plant matter the animal content often quickly becomes “mush” faster than the vegetable matter, where the green color persists through the early digestion process. Thus stomach contents appear primarily plant matter. But the likely primary reason was indicated by "drstressor" in DIED's post that read: "While they ingest plant material, they are really living off the insects larvae and zooplankton that live in the green stuff."

Numerous fish ingest plant matter incidentally along with the insects they consume. (See my last paragraph). Fish do not have fingers to separate bugs they eat that are entangled in filamentous algae or attached algae. Many "bugs" and soft worm like critters live in and among the various forms of algae and fine leafed underwater plants. Quickly removing just a bug with 6 clasping legs from FA with just your mouth would be a relatively difficult even if you had fingers. Most observers of fish have seen them ingest and then quickly expel items from the mouth in attempts to separate food items, crush, or turn a large item for easier swallowing. IMO loosely schooling fish quickly learn not to do this because “buddies” quickly dart in to eat the easilly available item. Then the original collector is “foodless” for his efforts. Soon the collector(fish) learns - I’m not doing that again it is not rewarding!.

Thus a feeding fish among neighboring fish, probably does not mind ingesting a little algae or benthic plant material with the bugs as long as the fish gets the bug/s. No doubt even significent amounts of fresh dead or decaying plant material is occasionally or frequently ingested depending on who the BG is currently grazing on or targeting. Numerous species of fish no doubt get in the habit or routine of eating one type of "bug" when those "bugs" are seasonally abundant in specific habitats or niches. This specific grazing behavior that involves eating plants with the protein will probably continue as long as the bugs-in-algae are readily available. Thus when the food is located among plant material one will get some “greens” with the protein. When the specific source is depleted or dwindles the fish usually move on to "greener" more productive "pastures" that likely will not be associated with so much lettuce.

Related to this topic Steve Spotte in "Bluegills Biology and Behavior" says BG are reported as insectivorous, planktivorous, omnivorous, and piscivorous including cannibalism. He states aquatic insects are the staples of the BG diet. He says they also eat plants and at times plant material can comprise from 16%-50% of the gut contents. Spotte questioned if algae/plants met the fish’s metabolic requirements. Above, I explained my thoughts about how plant material gets into the diet of BG. Although Spotte does mention a morph or strain of BG in Japan that is specialized for feeding on aquaic vegetation (Ecological Research17:49-57).


I propose that if a 3” or larger BG is placed in an aquarium or other similar container with consistently good water quality, a healthy group of plants including FA and the BG is not fed anything the fish will not eat any of the plants until it starves to death.

Ewest do come back sometime later after others have had a chance to reply and tell us where you were going with this.

An entire long article could be written on the foraging habitats of BG. Bob and Bill hit the nail on the head with their posts.

A couple points. BG are foraging generalists because they have to be as they are often the largest foraging population in the water body. Even a large source of food will not alone or primarily feed them for example like snails for RES. They simply have to eat a lot of stuff of different origins to survive. A good reason supplemental feeding helps BG populations so much.

Second the studies are as Bill notes one north one south. Winter in the North and BG have to feed down in the water column and eat worms and crustaceans from the detritus as its to cold or frozen over for them to forage long in the shallow weeds. In the south the BG have to stay in the shallow weeds mostly all year. In winter its plenty warm enough for bugs to grow in the shallow weeds an BG to stay there and feed. On the other hand for much of the year in south Fla in shallow waters ( 10 ft deep or less) the BG can not feed in the detritus on or near the bottom deeper than 6 ft +- as there is not enough O2 (below the thermocline).

The book Bill cites "Bluegills Biology and Behavior" is excellent. It notes a lot of outstanding info including the following of wrt this topic. OFM - Optimal Foraging Model is based on the premise that animals select food offering a net gain in energy above the costs of foraging for them , and that sustaining this positive balance necessitatiates periodic switching to more energetically profitable habitats. Profitable habitats are those containing the food resources necessary to temporarily sustain optimal foraging rates. I would add those habitats must be where the BG can have the required O2 and temps. Its part of the energetics model.

There is lots more to BG foraging like effect on lake dynamics , diel feeding patterns , other foraging models and more. Lets keep learning.

I've been too busy trying to set up a new dental office to participate in really fun threads like this. I've only scanned and not studied what I see above, but I think the discussion and assumptions are spot on that are made by Bob, Bill and ewest. I have as many as five tanks simultaneously running with bluegill ranging from 1 inch up to 9 inches, and it is virtually a 100% certainty that once a pellet hits the bottom, the bluegill will not eat it. They will simply let it rot. But if a nightcrawler is introduced, the bluegill will take it off the bottom.

Any guesses what how the bluegill respond to a dead fathead minnow on the bottom?

If you look specifically at the question as to whether bluegill switch to vegetarian mode or not, I think Bill has made the best argument. Vegetation is not "selected" by the bluegill rather it is ingested incidentally while picking up invertebrates whether they be macroinvertebartates or larger zooplankton. I've gutted catfish with stomachs full of filamentous algae. I've hypothesized that the algae existed in their guts because the invertebrates being targetted were entangled in the vegetation. Without hands and fingers, what's a fish to do? It eats the prey including its (the prey) food source/habitat.

To the best of my knowledge, bluegill lack special adaptations (morphological or biochemical)that allow them process aquatic weeds. Maybe someone can enlighten me, though.

Perhaps when the bluegill bite is slow next year, I'll test the argument and see if I can get a bite with a hook and piece of lettuce.....Uhhh, a piece of lettuce with no insects on it. I won't hold my breath. In summary, I think its a bold claim to suggest that bluegill switch to eating vegetation and that's why the bite is slow certain times of the year. I bet the vegetation is just an incidental ingestion to get to the good stuff.

Good stuff, guys. I have often wondered if heavy feeding is a direct or more indirect reason for large WR of BG. Do the % that hang around waiting for the feeder to go off actually grow that much faster, or does it, in part, give the ones going to the natural buffet bar a smorgasborg?
If a certain monster BG producer would 'sacrifice' just one giant specimen to examine the contents, we could get much needed information regarding it's eating habits.
I am still at odds with my decision not to fertilize this spring, in order to not feed the BG spawns, which should reduce competition for the larger BG. BUT, since the one study indicated that BG stayed on zoo until 7-8 inches, will I be making a mistake?

Having run both RES and BG in a PBR, my BG leave pellets on the bottom of the tank like Bruce has observed; RES seemed less likely to do so.

RES left the few dead FHM both floating and setting on the bottom. I have only fed Gambusia to the BG, and they all got eaten quickly with no dead ones to be seen.

In my aquarium BG did not eat fish food (pellets)off the bottom. However if I put small tadpoles or craws in and they lived long enough to get to the bottom in the rocks the BG would root in the rocks until they were found and consumed (feeding frenzy). Shawn I will check some more tonight. See your copy of "Bluegills Biology and Behavior" starting on page 33 IIRC.

Burger can you provide the specifics of your situation ? Visibility , feeding etc.

Regarding Wr, I believe it to be a function of a combination of things...starting with plenty of the "right" kinds of food all the time. Second, and as importantly, are genetics for aggressiveness and size. Third, dynamics of the population of the rest of the fish. Fourth is age. When Bruce caught that giant bluegill at LL,2 last July with Aaron Matos, that made the cover of Pond Boss, both those guys caught a number of similar fish that were slightly smaller. Those slightly smaller fish may have been three or four ounces lighter, but they are the same age and have the same feeding opportunities as that larger fish that was just short of two pounds. The biggest one had a Wr considerably better than its buddies. Why is that?

Be it know to all Pond Bossers, that I, JHAP, started this incredibly interesting thread that sparked a discussion amongst the Pond Boss scientific elite, bluegill aficionados and expert pond gurus including the likes of Ewest (with his unsurpassable research skills), Bill Cody (who needs no introduction), Bob Lusk (THE Pond Boss), Bruce Condello (that's MISTER Big Bluegill dot com to you sir), Theo (put NASA on hold, I'm moderating on Pond Boss) Gallus, and a rare appearance by Shawn Banks, including cameo appearances by DIED and Burgermeister thus resulting in my eighth (yes thats 8) informative post.

This thread is proof of the theory that any idiot can sometimes come up with a great thread, wait a minute, that didn't come out right, and illustrates the point that there are no dumb questions on Pond Boss, ok well sometimes there are dumb questions, but mostly there are no dumb questions and therefore if you have a question you should post it and it might inspire a great discussion such as the one created here by JHAP although it is unlikely that will quite a good as this wonderful thread that JHAP created but it will probably be a very good thread, my point is post away.

Carry on with the interesting, JHAP inspired discussion, that was created by JHAP.

I have been feeding some Purina Fry Food to one inch BG. This stuff sinks pretty quickly and they don't eat it very well. Actually, they don't seem to know what to do with it. However, my larger BG often pick it up and eat it when they run out of the good stuff on the top. They don't seem to do that with regular pellets.

I have noticed that even the fry prefer the standard sized pellets.

I haven't bought any sinking feed in years.

It was bigger because it could see the prey better. Bigger BG have better vision than smaller ones and can extend the probability of prey encounters over longer RDs (reaction distances) . Better vision also increases the probability of successful capture. The probability of successful feeding is the sum of probabilities of every step in the predation sequence ( location ,identification ,pursuit or stalk and capture ). Interesting isn't it. While this is a factor the main reasons for differences in RW are noted in a new study. See the PB thread link below. Genetics, Population ecology , Energetic history , and Species bias .


http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Main=11614&Number=141351#Post141351

WRT feeding choices - GSM (Greatest Stimulus Model) a foraging fish will peruse which ever prey item offers the greatest visual stimulus. Bluegill prefer moving prey and apparently learn to recognize specific organisms by their movements.

There is an absolute, distinct difference from the most giant fish to those just one slot down. I believe I could buy into Eric's explanation. To further that thought, I have seen some outstandingly cool things in the world of pond management and that explanation certainly fits.
Here's a story forever embedded in my beady little fish brain. Back in 1985, I electrofished a chocolate-muddy pond on a west Texas ranch. This "pond" covered about 30 acres and had been muddy its entire life. It was about 10 years old and the game manager had tossed a few Florida bass into it during its 3rd year...about a year after stocking a few bluegill.
Well, we shocked up a handful of stunted, pale bass in the 10-12" size class. They looked terrible. Horribly underweight and their slime had a yellow-clay tint to it, these fish weren't fit to be thrown out. I pulled some scales to age these critters (I was surprised to learn they were only age 3).
In a flash, this giant splash roiled the water in the front of the boat and the netter captured a giant bass. As it quivered from the electrical tetany, I shivered. I had never had my hands on a bass so large. We put it into a number 3 washtub, but the water was so muddy, all we could see was its back. I stepped on the footswitch again and I'll be darned if there wasn't another giant splash and we boated a twin. Each of those monsters weighed well over 13 pounds. What puzzled me then (very early in my career) was how these two fish could possibly make ends meet in a lake where they couldn't see a fraction of an inch and the food chain was virtually non-existant. I think we shocked up no more than 15 of those 10-12 inch bass, maybe 75 large bluegill and those two monsters.
I scratched my head, thought about it, called people I knew and could not for the life of me figure it out. It made no sense at all.
Then, the next year, we surveyed a similar lake elsewhere on the same ranch with the same results. Amazing.
As time has rolled on and my beard began to turn gray, things began to make sense.
Those bass were the tiniest percentage of fish which were able to adjust to that adverse environment. They were the Daniel Boone's of the muddy waters.
I believe these bluegill are the very same way. A handful "figure" it out with whatever senses they have that they can hone and focus on. What makes it so much more amazing is these wet little creatures can't think their way through these "problems." They have to be born with the genetic ability to adjust and thrive and then their tiny little brains must to adjust to the conditioning available.

Bob I think your big bluegill was that way because of a combo of Genetics, Population ecology , Energetic history , and Species bias . Better sight is just one of the species bias factors along with the other morphology factors.

I completely agree!

Bob, great story. What became of those 2 big bass?
Did you ever go back and shock them up again?

bluegills eat vegetation for the same reason JHAP ate DWIED's BS.....to get the bacon.