Methylene Blue

I am raising Killifish by picking eggs from yarn mops. After picking they go in a hatching solution of tap water, salt and methylene blue. I have never had any reason at all to use this stuff ever. For my use it identifies fungused and infertile eggs and prevents fungus. Saprolegnia. Never knew it had a name. Anyway, when I bought the stuff the guy in the LFS asked if I had a sick fish. I told him what it was for and he even knew about that. Now I read that some people use a hatching solution of bottled water with an alder cone soaking in it. Others use salt only. This methylene blue is nasty stuff. I spilled one drop in the bathroom sink and practically had to sand it off. Seems to me that when fry hatch in this stuff that it would be toxic to them, so I am using half the recommended amount. No problems so far. Rambling a bit here and don't know where I'm going with this but I guess I want to know. What is this stuff and is it anything for a goof like me to be playing with ?

methylene blue is good stuff doing no harm to the eggs or fry and as you have found out its very messy lol.
when you pick the eggs off they should be kept in the same tank water or at least that's the way that I do it you don't need to use a strong solution of methylene blue just just enough to tint the water any eggs with fungus will stain blue

some danio eggs you can clearly see the good ones

fish48 said:

methylene blue is good stuff doing no harm to the eggs or fry and as you have found out its very messy lol.
when you pick the eggs off they should be kept in the same tank water or at least that's the way that I do it you don't need to use a strong solution of methylene blue just just enough to tint the water any eggs with fungus will stain blue

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Thank you. That's good to know. I use about half of what's recommended just because chemicals scare me. And are you ever right about that stuff being messy. Two drops in my three quart container really comes up blue and if I ever decide to tie dye a T-shirt I'm going to use that stuff. Still, I am never going to put any in my tanks with fish and plants. This stuff makes me nervous. One other question @fish48 , have you ever heard that methylene blue is unstable ? One source says mix new hatching solution every four days and another says it will keep for a month if stored in the dark.

Good question I don't think I've ever read the instructions on methylene blue I probably did about 30 odd years ago. I knew back then that it was good for treating white spot and treating fish eggs. these days there are many types of treatments that are far better than methylene blue and probably less messy I have not heard of any danger when treating fish eggs I have been using methylene blue for many years and never had any issues when treating fish eggs to be honest I don't measure out how much I'm going to use I just add a little bit the water just enough to turn the water a light blue if any eggs go fungus It's usually within the first 24-48 hours methylene blue attacks fungus and prevents it from spreading the methylene blue that i use is made by interpret i have been using the same onefor more than 2 years I don't have it in the original bottle because of leaking and no longer have any information leaflet that may have come with it I only add methylene blue once I don't store it in the dark I keep it on top of one of the fish tanks ,

I got a pair of leopard danios to spawn this morning I treated the eggs straight after spawning

Thank you @fish48 . I'm going to stop worrying about it. It's just that things I've never used before spook me.

I hope that I have helped in some way

fish48 said:

I hope that I have helped in some way

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It did help. Thank you.

You don't need salt with the killifish eggs. Killis come from soft water and are usually found in pure rainwater. They do not occur in brackish water and do not need salt.

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Make sure any tap water is free of chlorine/ chloramine because these will kill the developing embryos or fry when they hatch.

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I never used methylene blue on my fish eggs. If they are fertile and kept in clean water, they don't normally get fungus.

Methylene Blue is used to kill bacteria, fungus and a few other microscopic organisms. It also increases the oxygen level in people and animals that ingest or are injected with it. It's used in hospitals to treat some medical issues and is considered safe.

The main drawback to Methylene Blue is it stains everything blue. The blue does fade over time and bleach will help to dilute/ remove it from tiled floors or benches.

@Colin_T ! ! ! I can always count on you for the straight dope. What you have said demystifys several issues I am having. Thank you !

Good luck with your eggs. I never had to deal with fish eggs before. Had plenty of live-bearing fish have babies but never found any eggs in my tanks.

Retired Viking said:

Good luck with your eggs. I never had to deal with fish eggs before. Had plenty of live-bearing fish have babies but never found any eggs in my tanks.

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This is a special situation. Things are set up in such a way to harvest the eggs, which are laid a few at a time daily, by artificial means. These fish will also spawn in a heavily planted tank and fry will appear. European aquarists prefer that method claiming that the resultant fry are more vigorous. I am going to do both ways just for the experience. @Colin_T raised a point that has bothered me. The salt and methylene blue hatching solution seems, to me, to be a toxic stew. When the fry hatch, and my eggs are in Petri dishes with but a quarter cup of water, they come alive in a toxic waste. These are tiny little things. Lots of guys do it that way and are successful but I don't like it. It just ain't right somehow. I am glad that Colin has similar thoughts. I've never gone wrong by heeding his advice.