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Aggressive Bluegill

I caught a bluegill while fishing several months ago and put it in my 250 gallon tank. It does well with the other fish (catfish, crawdads, minnows, goldfish, bullfrog tadpoles, etc).

Recently I caught a couple more bluegill and added them to the tank. The original bluegill went from hiding under cover to chasing the new ones around and biting at their tails which eventually killed them.

I have read of other people keeping multiple bluegill together in a tank so I don't understand why mine is causing issues. Why is this bluegill so aggressive?

Thanks,

Nathan

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Replies to This Discussion

Permalink Reply by Two Jay on July 14, 2011 at 10:40am

Territorial. It may be in a spawning mode, depending on water temperature.

Permalink Reply by Meg Stout on July 14, 2011 at 12:13pm

I had ~10 bluegill and a mess of minnows in my tank when I introduced 50 more bluegill this past April. All the minnows disappeared within two days, and small individual bluegill from the new population started showing up dead and partially eaten.

I think three things were going on.

First, the larger fish like to eat them some fish - after munching up all the minnows, they still wanted some fresh fish action.

Second, the fish were stressed (new tank, 24 hour period without aeration other than the siphoned water. Once the small bluegill were weak or dead, the other fish decided to nip off yummy bits.

Lastly, my tank lacked habitat where the smaller fish could hide. I ended up adding a floating mesh bin for the tiny fish, and the fish deaths almost entirely stopped. One, the tiny fish I could catch were in the mesh cage, and the ones I couldn't catch (fast little nippers), could zip behind/below the mesh cage if anyone (fish or aquapon) were chasing them.

I removed the mesh cage once the "little" guys weren't so tiny anymore. I see tiny guys in there still, but I suppose everyone has learned to co-habit nicely.

Permalink Reply by Jim Logios on July 14, 2011 at 2:22pm

When I got 25 bluegills from The Fish Wagon (small 1- 2 inches long), they went into a 50 gallon glass aquarium at school. They remained there for about 2 weeks. During that time, I noticed that the "big guy" was being a bully. I quarantined him for a few days, but it didn't help.

Once I got them home and into their permanent tank, I no longer see that behavior... even though the "big guy" is now 2-3 times the size of the smallest ones. I have a feeling the "big guy" is a hybrid that got mixed in...

Permalink Reply by Meg Stout on July 14, 2011 at 3:22pm

I should mention my bluegill are actually hybrids (i.e., great big mouths).

Permalink Reply by Green Acre Aquaponics on July 14, 2011 at 7:49pm

We don't have Bluegill but had a similiar problem with agressive Tilapia as soon as we started reaching warmer temps. We had a couple mortalities and both presented with some pretty significant puncture wounds. We attributed this to spawing behavior as the males can get a bit aggressive. Some habitats that were simply 16" lengths of 6" solved the problem immediately.

Interestingly we have had some interesting aggressive behavior from one Tilapia we have since named Cujo the Killer Fish. Cujo had made a dash for freedom one day when the lid was open and apparently injured himself upon landing. We scooped him up quickly and put him back in the tank. Soon we noticed he was doing the sideways dance and knew that if we left him in the grow out tank with all the others, he would quickly be beat up and perish. We netted Cujo out and he was given a new home by himself in a nursery tank. After several weeks Cujo recovered and he went from cowering in a corner far away from any predatorial heads to slowly approaching the surface, posturing by opening all his fins and then charging the surface! He will lunge at the edge of the tank and spash anyone near by. It is quite entertaining when he does this to some poor unsuspecting visitor especially when their back is to the tank. We have finally captured Cujo's antics on video. I will have to get it uploaded soon.

Permalink Reply by Nathan on July 14, 2011 at 9:11pm

Thanks for the comments everyone.

Green Acre Organics, what do you mean by habitats?

Thanks

Permalink Reply by Green Acre Aquaponics on July 14, 2011 at 9:23pm

Hi Nathan, I am not familiar with Bluegill behavior, but I would guess spawning/mating behavior is somewhat similiar to that of Tilapia and other fish. If habitats are provided, they are more likely to breed as there is some kind of "habitat" for the female to retreat to. In a natural setting that may be under a rock or submerged tree branch. In our man made containers, we can provide similiar hiding places with large sections of PVC pipe or even a terra cotta pot. We found once we introduced these, not only did we start seeing breeding, but as I mentioned before, it eliminated the issue we were having with aggression by providing safe havens. You may find similiar success with your issue by simply tossing in a couple of flower pots!

Permalink Reply by TCLynx on July 16, 2011 at 2:22pm

It is also not uncommon for bigger fish to become quite aggressive sometimes. I've hand and herd of other people who have had a big catfish chase other catfish right out of the tank.

As to bluegill being aggressive, other than seeing a bluegill fingerling in my tower tank seeming to guard the area in front of the camera for a few minutes, I've not seen mine be especially aggressive. I have been told though that tank culture of bluegill can make them more aggressive than they would be in the wild (I expect this could be largely due to the lack of hiding places in most tanks.)

Permalink Reply by Cindi Conway on November 12, 2014 at 7:31pm

Hi! We bought a farm 6 months ago that has a 2000 sq ft aquaponic greenhouse. It had been unused for a period of time and the FT only had 6" water and what looked like to be about 3 dozen BG. I wanted to eat tilapia and decided to move the BG to a smaller tank so I could put tilapiain the main tank. I thought all of them were gone when I added 300 tilapia and 60 catfish fingerlings. Needless to say, the fish started disappearing at an alarming rate! I had to drain the tank of 3000 gal. to catch the 5 sneaky remaining BG. They can be very cannibalistic at times but are by far the hardiest of fish. Since I started 6 months ago,I've lost 700 tilapia and catfish. I finally decided to stick with the BG. No matter what issues I've had, the BG handle the stress better but don't eat each other if water conditions are good. Live and learn.