Daisy's rice fish hatching rates?

[Cyprinodont]

Hello there! 

I've been breeding this group of Daisy's rice fish (Oryzias wowrae) since the beginning of the year. This was my second year breeding rice fish in medium sized outdoor mini-ponds. I was mildly successful with colony breeding them as long as I had green water, which luckily I did almost all summer this year so I was able to more than double my original 9 adults and bring 21 fish in for the winter. 

Since I brought them in I've been trying different methods of breeding them since there are so many fish now, and the smaller juveniles are particularly ravenous for newborn fry I haven't had any appear in the colony. 

I HAVE however collected a ton of eggs by just grabbing the females I see with large clutches and stripping them off into specimen cups with methylene blue solution. I've probably collected around 100 eggs just casually every few mornings. 

So, all of that is to say, my problem isn't "how do I breed medaka" I've got that figured out, I've got tons of eggs. What I don't have is... Fry. I've been collecting eggs for 3 weeks and they're all clearly fertile, developing well, I only had a few that I had to remove from the methylene blue. But even my oldest eggs haven't hatched yet, despite having had visible eyes since week one and clearly seeing them basically fully developed since week 2. 

The temperature in their hatching containers is the only issue I can think of. It's about 74F which is just room temperature. All the lab reports say they have a 10 day hatch at 77F, but I'm not sure if that's an equation you can use to see what the hatch rate is at lower temps. Even so, they've passed that date as well and still no hatches. The adults are kept at 77-78F. I check so many times per day and I know exactly how many eggs are in each container, so none are hatching without me knowing and somehow dying/ disappearing. They're in small 2oz cups. 

Here's the best picture of them I can get with my phone:

This is the first batch of 10 eggs I pulled on Oct. 19th. I've fully changed them out of the methylene blue at this point because I wasn't sure if that was hurting things despite it being used in almost all the laboratory reports of breeding at scale as well as many hobbyists. 

Any advice on whether this is a normal variation of hatch rates later in the season, what I could do to speed things up, what kind of incubators people use to hatch rice fish eggs and keep them warm, would all be greatly appreciated! 

Edited November 11, 2023 by Cyprinodont

[Revaria]

Huh this is an interesting project; I didn't realize you could strip the eggs of rice fish and still have them be viable. I don't know what the average hatch time for rice fish would be, but I don't think temperature variations would change the hatch rate for more than a few days. Your fish seems to be developing quite nicely, but if they aren't hatching or are disappearing that means somewhere along the line they failed.

How large is the container you are using to hatch the eggs and are you using air circulation as well to circulate the water. My experience with smaller containers is that the water would foul faster so the batch would have an increased chance of going bad if a few eggs went bad. My hatching tanks are usually in a 2.5-gallon tank with a fast air bubbler and a small heater, if necessary, higher temps increase the hatching speed, but I usually try to keep it around 77-78 unless other fish keepers mentioned some pertinent information. There is always an extra mop to break up the flow of the water as well, to prevent the new born fry from being taken over by the wave. And I don't know if this matters, but the environment of the tank is usually naturally dark as well due to the nature of my fish room.

[Cyprinodont]

On 11/18/2023 at 11:44 PM, Revaria said:

Huh this is an interesting project; I didn't realize you could strip the eggs of rice fish and still have them be viable. I don't know what the average hatch time for rice fish would be, but I don't think temperature variations would change the hatch rate for more than a few days. Your fish seems to be developing quite nicely, but if they aren't hatching or are disappearing that means somewhere along the line they failed.

How large is the container you are using to hatch the eggs and are you using air circulation as well to circulate the water. My experience with smaller containers is that the water would foul faster so the batch would have an increased chance of going bad if a few eggs went bad. My hatching tanks are usually in a 2.5-gallon tank with a fast air bubbler and a small heater, if necessary, higher temps increase the hatching speed, but I usually try to keep it around 77-78 unless other fish keepers mentioned some pertinent information. There is always an extra mop to break up the flow of the water as well, to prevent the new born fry from being taken over by the wave. And I don't know if this matters, but the environment of the tank is usually naturally dark as well due to the nature of my fish room.

So I have confirmation that they are in fact viable! 

After this post I did some thinking and seperated the eggs into smaller specimen cups that I had with lids and put them on top of the light. They definitely stay warmer this way and I can separate the eggs more because I have seen good research that the more eggs in a small amount of water, the lower the hatch rate is, with the ideal being 2 per container. I have more like 6-10 but more water than was used in those experiments. 

Since then I have about 2-5 hatching every day. It's the first thing I check when I wake up and move them over to the fluval breeder box on the tank, I think I have over 15 in there now but it's so packed with java moss it's hard to count. 

They definitely do not all hatch at once like say, tetras, though it does seem like the cups that have hatches tend to have more than 1 at a time hatching, Ive read some things about "hatching enzymes" released by the fry to soften the shell of the egg and allow them out, too much of that on a less developed egg could maybe damage it and soften the shell prematurely allowing fungus? 

I've only had fungus in one of the cups so far and I still had hatched from that cup, I just separated the fungused egg mass. 

It's really hard to separate the eggs gingerly since they're so sticky and wrapped in filament but I think I'm going to experiment with using something to separate them into maybe groups of 2 and keep trying with these specimen cups. 

Picture of the current set up. I check the cups before and after work, or multiple times a day if I'm not at work, and move the fry to the breeder box on the left which has an air lifter providing constant fresh water and movement. I feed sera micron, repashy powder, frozen baby brine shrimp, and there's also lots of java moss and a piece of almond leaf. I clean out the bottom of the container regularly with a pipette. 

All the fry I've moved seem to be still alive and eating. I just today started with the brine shrimp to see if they can eat it yet, the oldest are about a week old. They're definitely free swimming as soon as they're born, and strong swimmers too, which you would hope with such a long gestation. Within 12 hours max after hatching they can evade my pipette pretty well and they aren't harmed by being sucked up and transfered, they swim right out the end! 

[nabokovfan87]

On 11/11/2023 at 2:04 PM, Cyprinodont said:

I've been collecting eggs for 3 weeks and they're all clearly fertile, developing well, I only had a few that I had to remove from the methylene blue. But even my oldest eggs haven't hatched yet, despite having had visible eyes since week one and clearly seeing them basically fully developed since week 2. 

You'd want to remove the fry from the methylene blue as soon as they hatch.  There is a lot of research papers out there regarding the use of methylene blue and it would explain that situation/logic in detail.
 

On 11/11/2023 at 2:04 PM, Cyprinodont said:

what I could do to speed things up, what kind of incubators people use to hatch rice fish eggs and keep them warm, would all be greatly appreciated! 

The ziss tumblers are pretty good. I've also heard of people using neocaridina tanks to keep the eggs cared for.  Both of those seem like good options for this setup. 

In terms of increasing the yield, thats where I would start.  In terms of the fry developing, if you run into issues I would start with how you're feeding them (if there is any concern there).

[Cyprinodont]

On 11/20/2023 at 1:25 AM, nabokovfan87 said:

You'd want to remove the fry from the methylene blue as soon as they hatch.  There is a lot of research papers out there regarding the use of methylene blue and it would explain that situation/logic in detail.
 

The ziss tumblers are pretty good. I've also heard of people using neocaridina tanks to keep the eggs cared for.  Both of those seem like good options for this setup. 

In terms of increasing the yield, thats where I would start.  In terms of the fry developing, if you run into issues I would start with how you're feeding them (if there is any concern there).

Pretty sure I said it but I remove the eggs from the methylene blue before they even hatch, let alone letting the fry swim in methylene blue. The methylene is only used for the first 1-2 weeks of incubation of the eggs to prevent fungus while they develop and it is changed out as the containers get 99% water changes every day in absence of circulation. 

I've considered egge tumblers but I'm not so sure that's a good idea with rice fish for a few reasons, the eggs are hardy sure but still kind of fragile, I've crushed them before with tools while trying to separate them. They're also very sticky so they would probably all just form a giant mass inside the tumbler with circulation being entirely cut off to the ones inside the mass because, you would need a LOT of tumblers to do the amount of speration that I am currently doing where I'm trying to minimize the number of eggs in each hatching container, and with how long they take to hatch I would need like 20 tumblers running, that would be rather pricey compared to my current $0 set up lol. I might experiment with tumbling the eggs but I don't think it will work en masse. 

I think the best set up is one of these fluval air driven breeder boxes. You would still get the circulation and water volume benefits but with way lower flow and higher volume inside the container to separate the eggs from each other. 

Edited November 20, 2023 by Cyprinodont

[nabokovfan87]

On 11/20/2023 at 5:55 AM, Cyprinodont said:

I've considered egge tumblers but I'm not so sure that's a good idea with rice fish for a few reasons, the eggs are hardy sure but still kind of fragile, I've crushed them before with tools while trying to separate them. They're also very sticky so they would probably all just form a giant mass inside the tumbler with circulation being entirely cut off to the ones inside the mass because, you would need a LOT of tumblers to do the amount of speration that I am currently doing where I'm trying to minimize the number of eggs in each hatching container, and with how long they take to hatch I would need like 20 tumblers running, that would be rather pricey compared to my current $0 set up lol. I might experiment with tumbling the eggs but I don't think it will work en masse. 

Yeah, I was thinking about this.  The nice thing about the ziss ones is that the eggs can be set so they barely wiggle in place. It isn't easy to spread out sticky eggs, but it's one of those things that might really help with the hatch rates.

Part of me wonders if you used floating mops as opposed to pulling eggs off the fish, if that would help dramatically or not. Tough to say.

If you're wanting to really hatch hundreds of fry, maybe there's a balance between removing the eggs or a dedicated egg setup, making fry bins like Dean or some other methodology that makes sense (specimen containers and rigid airline or something). Have a setup of 3-4 "hatching bins" and rotate batches in?

I'm terms of temp, finding a way to float the tubs in the water would help with temp.

Here's a setup I liked for barbs, very low budget, but it works well.

 

Looking forward to seeing how you develop your process in the future!

[Revaria]

Its good to hear that you had success rearing the fry, I'm surprised they take baby brine already as they are quite tiny. I'm just feeding mine the 5 - 50 micron golden pearls I use for my Boesemani Rainbows, I'll just transition to live baby brine and flakes later on.

I'm not sure how well egg tumblers would work for you, they work well enough the times I've used them for shrimp, but it was always a pain getting them into the actual tumbler for me mops or plants was always just easier as no one seems to get enough free time nowadays. A mass of eggs also didn't seem to bother the eggs much as long as the rate in the tumbler was good. Also if your fish are out swimming your pipette, get the turkey baster lol.