Aquarium cannibals!

[Deck]

A couple of my aquarium freshwater fish have turned cannibal (Hannibal Lector would be proud!) and are chasing and munching on the fins of others! Can anyone offer any advice? The attacking fish is a small koi-type fish. The other - surprisingly - is a fairly ornamental looking fish. The victims so far is a Lionhead (now floating on the top minus all fins and most of its tail), and a Redcap who is now finding it hard to swim and stay below the surface. There are 12 fish in the aquarium - it is 4 feet wide by about 1 foot.

[KEJ2000]

Dear god! Separate the killers from the victims! I think fish will only attack each other like that if they are all starving from an insufficient amount of food. Try feeding them all much more, making sure that each fish gets some (i.e., that a single, aggressive fish isn't eating up the food of all the others). Also, check to make sure that your fish food is "nutritionally complete", offering the necessary amount of protein and vitamins, etc. They may be desperately trying to increase their protein intake when they chomp each other.

[pezza.......]

Also check that the reason the for the fin loss isnt some disease such as fin-rot. This desease eats away at the fins of the fish and other fish can try to eat the loose parts! Not nice but can be caused by poor water conditions and treated with a simple tonic available from most good aquatic shops.

[molly]

I would also advise you to make sure there are plenty of nooks and crannies for the more vulnerable fish to hide in. Put in some weed as well, but make sure you get it from a reputable shop in case it harbours unwanted pests or disease.

[sft42]

Sorry to disagree but KEJ2000 is wrong....most people with aquariua over feed if anything and most fish aggression is due to territorial squabbles and not food.....Ornamental fish from the carrasius (goldfish) familyhave been inbred for centruies by the Japanese to develope the fancy oranda and lionhead varieties and they are very prone to swimbladder disease....you should check the size of your fish against the volume and filtaration of your tank....it does sound as though you might be slightly over stocked here....other things you can do it to re-arrange the decoration in your tank which will let every one establish new ground and try doing a partial water change every other day of about 20% of the volume (not forgetting to de-chlorinate the water first) which will help with any fin-rot problems.

If you need any more help then please repost with more info on the full tank size, fish size and varieties, and the filtration system used...include also anything else you have in the tank...heater and air stones and I will see if I can help more.

[KEJ2000]

Jeez, sft42!! I have kept fish my entire life!! And they have lived long lives! You don't know that Deck is already overfeeding.

[firefly]

I have to agree with sft42 and say its territorial. My budgie did the same thing (ate other budgies, not fish). KEJ200 you have probably been lucky in having fish which get along.

[sft42]

Sorry KEJ if that sounded abrupt but we are talking about saving some fishy friends here......Don't forget although you may well have done the right thing through your past the vast majority of people make the mistake of over-feeding more than any other problem in fish-keeping.

[sft42]

Please let us know how your piscine pals got on.....your aquarium amigos, carrasius cohorts....did they survive?

[Deck]

Hi everyone, & thanks for all your interest, support & suggestions. This aquarium has only been recently established so I did think SFT42 was right about territory etc. However, firstly I separated the main agressive fish to a separate "holding" fish bowl. I watched the remaining fish & noticed that the odd one or 2 were still chasing others and trying to eat their fins. This is definite attack and not finrot.... As an experiment I gave some food (additional to the normal feed I had been giving) and MIRACLE - they all started to behave. I have now increased their feed, bearing in mind not wanting to overfeed, & everything seems to have settled down wonderfully. So KEJ2000 - in this case - I believe you are vindicated, and all should bow to your specialist knowledge, in this - your obvious field of expertise! However, thanks to everyone else too for offering their suggestions... p.s. Obituary:- Unfortunately, it is my sad duty to report that the Redcap did not survive :-( The Lion head however is still alive though is floating on the surface, cannot swim at all apart from going in circles(no fins left - it's sooo sad) and probably will not survive much longer in such a state. It is pitiful to watch and most upsetting. Do fins ever grow back?? At least the others may now be saved. Regards, Deck.

[sft42]

Fins do indeed grow back....you need a product called MELAFIX which will help you fish get back to full health.....place the lionhead in the holding bowl and treat him/her there.

Having re-read through your original question I can perhaps see the root of your problem...Do you have standard goldfish (ie single caudal fin fish) in with fancy tailed fish? If so the fancy varieties will always struggle to compete for food and you will have to over feed constantly to make sure the do get enough food......Orandas, Lionheads and the like simply can't swim fast enough to keep up with shubunkins and sarsara comets and the like.......I would recommend trading one type of fish in and only keeping one sort or the other if you don't want to constantly have this sort of troubles cropping up......either that or buy a heater and go for some nice tropical fish like me :>) ....here's some pics of my favourite fish the botias macracantha or Clown Loach.

http://www.loaches.com/species_pages/botia_macraca
nthus.html