Never Put Water Melon In The Tank For Fish

[coolie]

Have a nightmare on my hands. Thinking it would be as good as cucumber for some types of cat fish, I put a large slice of water melon in the tank and checked back in the morning - half my fish are dead.
 
I have done a 50% water change and the remaining fish are no longer at the top (replenished oxygen levels). It's at this point I find out my air stones for emergencies don't work but I have to go to work now.
 
It's not completely clear but the fish look happier. The Rosy Barbs are hiding - they are upset.
 
I'm pretty upset as well as you can imagine. Just posting to find out if more water changes are recommended and to warn others really of this stupid mistake.

 

[Tongue_Flicker]

Water or juice extract naturally dripping from watermelons usually contains just water, glucose, fructose and lycopene. I don't think those are enough to kill a fish though. If soaked in water for a long time their sugars disintegrates as well. Dunno bout the seeds though. Did the watermelon still have seeds in it when you put it in?

 

[coolie]

There were no seeds, the water melon dissolved. I forgot to say that it affected my snail tank as well which I also put water melon in. You couldn't see the back of the tank it was so hazy, and stank of water melon.

 

[daizeUK]

My sympathies for your losses coolie

 

[dave840f1]

I'm sorry for your loss, but considering what watermelon consists of i'm not surprised. It has Fat's, Carbohydrates, Fiber, Potassium, Iron, Manganese, Sodium, Phosphorus, Magnesium, Calcium, Vitamins C, A, B1, B2, Niacin and Folic acid. I would not say you are stupid as we all as aquarists try to feed our charges with as a varied diet as possible. I'm sure we would not like to eat the same food every day and every meal.

 

[Tongue_Flicker]

Oh i see. I think i know what happened here, eating too much fruit generally causes colic in giant land snails and given the small size of aquatic snails in water tanks; have probably overdosed from the watermelon. Dead snails usually release a mild toxin in the water that are sometimes lethal to small fish

 

[coolie]

There's no snails in my main tank - if there were, they would be eaten in seconds by the Barbs. The snails I mention have their own tank and they have survived by climbing out of the water.

 

[Tongue_Flicker]

Haha! I'm out of ideas then. Have you asked around in other forums if you have other accounts?

 

[coolie]

I just want to update this for future prosperity. This was actually Melon, not Water Melon. I didn't know the difference.
By googling, I can see some people have successfully fed Melon to fish such as Plecos, and I feel sure they must have been using very small pieces which can be eaten quickly.
 
My Melon was very ripe and a large piece had dissolved by about 25% by the morning.
 
It turned out that some light aeration and only a 50% water change did resolve and the water cleared in 24 hours, however I have left my CO2 off and continued aeration as a precaution.
 
Sadly I lost one tetra and 4 lovely Rosy Barbs to the incident, nearly half my stock.

 

[Tongue_Flicker]

Melon has orange meat and watermelon is red or pink. Either one is technically safe as they easily disintegrate into the water system.

 

[coolie]

I'm not sure if I'm misunderstanding you but you seem to be at odds with what I'm saying. Half my fish are dead, so it doesn't matter whether it's technically safe. It doesn't have to be toxic or a carcinogen or whatever,
for it to pollute the water beyond the point where it can sustain fish.

 

[PrairieSunflower]

Could there be a possibility that the melon's skin was coated in something, maybe wax, maybe some other chemical for freshness or as a preservative.  A great deal of fruit in the grocery store under goes a "wash" in the packing plant that contains various chemicals to make the fruit last longer.

 

[coolie]

No, I peeled it with a potatoe peeler before putting it in. Although some of you are trying to blame some poison, you only have to look into what organic matter can do to oxygen levels by polluting the water. As the organic matter breaks down, it can depleat the oxygen. I don't knoiw the exact process, whether it be oxidisation or if it is the action of bacteria digesting the sugar and other organic matters that uses up the oxygen as I haven't had time to research. But lets just say that all the fish that survived were gasping for breath at the surface and I'm sure no toxins were involved. Lets not forget that I only did a 50% water change and the remaining fish are now playing in the filter flow which they only do when really happy, they are not sulking like they would be with toxins in the water.

 

[eaglesaquarium]

I'm guessing its related to the change in pH.  Fruits are notoriously low pH, whereas veggies are much higher in pH.  Have you checked the pH levels in that tank?

 

[mark4785]

I would hazard a guess that the melon contained something toxic to the fish. The chemical called niacin within the melon, when overdosed, can cause cardiac arrhythmias and a sudden raise in blood sugar in humans. Presumably the sugars in the melon were too much for the fish as most conventional foods given to fish are high in protein, fat and vegetable matter rather than things like sugar which get into the blood stream very quickly, particularly if its going to be consumed by something with a high metabolism (i.e. a fish in tropical water). Too much unused sugar (sugar that hasn't been converted into usable energy) in the blood can cause ketoacidosis (a sudden drop in blood pH) in humans and is fatal; presumably the same can happen with fish? 
 
I think I would definitely recommend sticking to vegetable and protein foods for your fish with the exception of things like blueberries (which aren't as sugary) for low metabolism / cold water fish such as Koi.