Angelfish, die one by one

First: I've had angels for 15 years in 10, 20, 38, 45 and 55 gallon tanks. I have 4 tanks at this time. Here is the situation.
A pair I've had for 6 years finally spawned on some Anubias. I move the eggs and had about 30-40 fry. They've been in their own tank since squiglers.
20 gallon High, planted tank Java, Anubias, Lilly.
3 otocinclus
2 amano shrimp
30 angelfish, size of 25cent US coin.(not counting fin size) They hatched in November separated from parents.
Water
pH 6.8 Nitrates 10 Nitrites 0 Amnia 0 GH 50 KH 40
3 small sponge filters and a 4 inch cube sponge filter. Also an Aqueon HOB filter.
This is my grow out tank. PWC is 10% daily and 50% once a week.

Just two weeks ago the mystery begins. Every couple of days, one dead angelfish is found.
In two weeks, I have lost 6 fish. Amano shrimp and otos are doing well. The other Angels are like a bottomless pit of hunger. Feeding is 3 times a day.
After the feeding, they seem to pick at anything for food.
My thoughts on this:
Maybe they are eating the shrimp pellets left in the dark for the amano japonica shrimp? This blocked digestion?
Maybe they ate some of the dead Black Beard Algae still on the driftwood? Some toxins from the dead algae?
Maybe they were overfed?
Feeding is like a shark frenzy, water splashing and food is gone quickly.
One last puzzle. The dead fish are never the small ones, always the biggest.
Okay, experts. . . let's hear some ideas.
thanks.

 

I am really new to this hobby, so take everything I say lightly. Could it be that you are changing too much water, and this rapid change and fluctuating ph is killing the fish? Pls correct me if I am wrong.

 

Yeah, I thought about cutting down on the water changes. But I had an ammonia spike in an older grow out tank and lost 20 nickel size angels in one night last year. See my 4 sponge over reaction in this tank? Also, I feed less often too. The strangeness is only 1 out of 30 seem to be affected and I thought the shrimp or otos would show stress. They dont!

 

The strangeness is only 1 out of 30 seem to be affected.

If it were me I would slow down on the WC, with NO3 at 10ppm and NO2 at 0 and ammonia at 0 maybe 20% 2-3 times a week?
If you breed fish you will have die off, it's just nature. I breed some angles but mostly apisto's and every batch I have some runts and some die off, 1 out of 30 is a pretty good survival rate.

 

I think need to take a closer look at the dead angels. Maybe something with the water or food.

 

Dead angels look fine. No bloating, no growths, no visual problems, full belly, feces released. I think they are eating something toxic off sponges or wood. I removed one sponge and driftwood with a white film on it. Two more dead today. I dropped temperature from 78 to 73 to slow metabolism and their endless search for food. I moved 5 to my adult angel tank of 38 gallons. They look energetic and ate minutes after the transfer. The 3 adults stopped fighting. 2 females and 1 male, about 5 inches each. For the 25+ left in the grow out tank, they have a new food supply.
I'm pretty sure it is dietary. Only some of them keep picking at sponges, leaves, and driftwood. The others just wait or beg for flakes. My next batch will go into a more pristine tank. Maybe no plants, wood or dead algae. My pair at work are doing a great tank raised batch of 40. Day 7 of hatching those blasted baby brine shrimp.
One last issue.
Tomorrow was my appointment with LFS to drop off 15 of this spawning. I’m feeling guilty about maybe sending him sick fish. Opinions ? I’ll decide in the morning, if anymore die off.

 

Hmm the white film seems to me like a unmatured tank or just too much food going into it. Cyanobacteria, some fungus and slime are mildly toxic to fish...although they may not kill adult fish, perhaps they could threaten juveniles? I would do 50% wc every few days since this is a breeder tank and only 20g. With breeding setups more water turnover is definitely a good thing especially due to the increased amount of food put into it.

 

update
With the herd thinning out I can see specific juvies going south. 2 more dead today. 4 are now not eating and are doing a flicker or shake in place at bottom of tank. the flicker is like if a person gets the chills and quickly shakes. They don't do this often, but I've seen each one do it now. The ones I moved to the adult tank are good. I'm afraid to take this batch to LFS.
I think my mistake was adding a new piece of spiderwood to this tank. It was up and running over 6 months as a QT tank for otos. I added the eggs and sponges. BBA did creep in with all the feedings. I might be losing this batch.

 

update
With the herd thinning out I can see specific juvies going south. 2 more dead today. 4 are now not eating and are doing a flicker or shake in place at bottom of tank. the flicker is like if a person gets the chills and quickly shakes. They don't do this often, but I've seen each one do it now. The ones I moved to the adult tank are good. I'm afraid to take this batch to LFS.
I think my mistake was adding a new piece of spiderwood to this tank. It was up and running over 6 months as a QT tank for otos. I added the eggs and sponges. BBA did creep in with all the feedings. I might be losing this batch.

I think there might be some toxins in the tank...

 

I believe you're right. I moved all the juvies but 2. (they hid well). Amano shrimp and ottos are still in but okay. Maybe it's a species specific toxin. I do have plants in pots that get little soil turnover. Maybe pockets of bad gas come off?
Well this mystery goes unsolved. I'll be taking this one down and hydrogen peroxide clean it. Start over with new sponges, free standing plants like anubia, and turn it back into my QT tank. It was never planned to be a grow out tank.
I do have another 20 High with 1 week old fry being parent raised. 40 or 50 doing well. Not sure what to do with that batch.
All the moved fish are doing really well. Exploring the 38 and 55, always looking for food.
Some blasted thing in that 20 is a hidden killer.

 

Where did the spiderwood come from? Was any insecticide used in the house? Need to look at everything that could have possibly came into contact with this tank...

 

3 pieces of Zoo Med spider driftwood bought a few weeks ago all at same time. I boiled one, the other too in hot water no boiling. One is in a 5 gallon at work with a Betta and clown pleco. Pleco won't get off it. Second one is in 38 with 3 adult angels, 6 corys, 7 otos and now some juvies. The third piece went into the 20 with the juvies, no survivors in that tank except shrimp and otos.
A web search uncovered this company has a bacteria problem on the wood. The thin white film doesn't go away but attracts snail and bioslime eating fish. So I now have to be careful of the moved fish spreading internal bacteria to the adults. I may have made things worse. I better be prepared for gram negative and gram positive bacteria treatments. Time will tell if I bought the farm with these driftwoods.
The 20 high has been in house and same place for over a year. No insecticides or chemicals in this house. Tank is in a corner away from most activities. It was the QT tank. Toxins would likely affect all fish or weak fish. Bacterial infections could spread and kill them off one by one. This is looking more bacterial now. I might be asking for medicine advice in the next few days.

Otocinclus have bacteria in their guts to help digestion, maybe that is why they're still alive.

 

I had a few deaths of the Juvies in the adult tank. Couldn't find any bodies but population is smaller. The corys are known scavengers but I should have taken a photo of the otos sucking on skeleton of one juvie. Only bones were left. Is it widely known that otos are not pure herbivores? So many juvies are swimming all over eating well and mixing with the adults. You can see a couple not doing that and staying near the bottom. Reminds me of a hex infection I had 5 years back. It moved from fish to fish and I had to do force feedings of meds to clear it up one by one. For this batch of juvies, I lost about 15 out of 50. Worst percentage ever for me. I think this will be the last post on this.

 

Im not familiar with Angel genetics, but a lot of heavily bred fish have recessive lethal alleles so having both of them will result in death...depending on what strains you have, maybe that's one possibility?

 

How it going? I had a spawn a month ago well over 200 free swimmers, I get dead ones every day 1-3 or so. I'm thinking it's par for the course. I've done everything I can do regular feedings, regular water changes and cleanings, no substrate and nearly bare tank beside a sponge filter and heater. Small fish die along the way in their development is all I can figure. The bigger the spawn, the more that make it.

 

I move them into 3 different tanks. Over the course of 10 days, everyone died the same way. Eating 3 times a day, next day won't touch food, then death that night. It is very fast. All my adults, otos, corys, shrimp are perfectly fine in the same 3 tanks. Maybe genetics? Well my new batch of 40 with different parents are doing well. The bums won't wean off of BBS. Guess I'll have to starve them a day to get them to stop spitting out the flakes.
What do you do with 200 angels? I need to find homes for the 40 juvies I have now. Completely parent raised in planted gravel bottom tank. Except for that tank, all my others have a fool-proof birth control. Plecos! Their tough hide is no match for agressive Angel protecting eggs. They eat every batch even with lights on and eggs near the surface. I've seen it?
I do envy your set up. I miss the days of bare tanks. 200 free swimmers? What size tank? How many sponges? Afraid of ammonia spikes?

 

I move them into 3 different tanks. Over the course of 10 days, everyone died the same way. Eating 3 times a day, next day won't touch food, then death that night. It is very fast. All my adults, otos, corys, shrimp are perfectly fine in the same 3 tanks. Maybe genetics? Well my new batch of 40 with different parents are doing well. The bums won't wean off of BBS. Guess I'll have to starve them a day to get them to stop spitting out the flakes.
What do you do with 200 angels? I need to find homes for the 40 juvies I have now. Completely parent raised in planted gravel bottom tank. Except for that tank, all my others have a fool-proof birth control. Plecos! Their tough hide is no match for agressive Angel protecting eggs. They eat every batch even with lights on and eggs near the surface. I've seen it?
I do envy your set up. I miss the days of bare tanks. 200 free swimmers? What size tank? How many sponges? Afraid of ammonia spikes?

Thanks for sharing!
Honestly, first time making it this far and 6th time trying to get this pairs fry to work out beyond free swimmers. it's a 20g I bred the parents in, I moved the parents out after two weeks of free swimmers, It's getting crowded now as they grow, but I'm scared some parameter will be different on my larger tank and kill the spawn through stress shock, like can't adjust and just shut down, so I haven't moved them and taken the leap. Maybe I move the largest, see how they adjust so I don't lose the whole spawn,see how it goes.

I have one large sponge filter that was cycled and off another tank, I do a 20% water change daily whether it needs it or not just to make sure it stays low, testing shows no issues, and so far so good. If it starts creeping up as they grow, I'll increase the water change size, but I don't see how they can all stay where they are for another week or two, it's tight and getting tighter.

Every time I've moved a spawn so far, be it a rearing jar to a tank, or fry from the breeding tank to another tank, it hasn't ended well, so this time I left them with the parents, crossed my fingers they wouldn't eat the eggs or the fry, and then removed the parents instead of the fry when the fry were pestering the parents and the parent were blasting me in defense when I came for cleanings. It was just getting stressful and they had to go before they ending up nuking the spawn.

Right now I'm trying to keep them alive and growing, it was 200 freeswimmers, I'm about about 120-140 fry currently after a month, and nothings died in the last 72 hours which is a first. I suppose I'll have to cull something from it at some point, I plan to keep 6-12 males, the rest I'm going to give to friends with tanks, and take to the local fish stores if they will take them, either for free or for a small store credit or whatever. I did it for the fish for my tanks and to accomplish doing it. I wanted to do it and get it done for years, not for the money at all, for the experience. if all else fails, craigslist I suppose.

Like right now I could cull 20 of them for being runts that have hardly grown and seem to be eating the bare minimum to survive. there's a dozen or so overachievers, and then there is the average pack. my guys are still small, biggest handful are approaching dime, the majority still around pea size up, and then those 20 little guys, like a grain of rice to a half a tic tac still. I'm sure I'm going to have losses still before I'm done. some look like fry, the majority look like little tunas or footballs, and the overachievers have the angelfish shape and got their pectoral fins, but that's been like a week tops now.

Also, I fed the Hikari first bites since day one, they took to it immediately, and feed 4x a day, about every 6 hours. I've got them eating some crushed and screened pellet and screened flakes for the last 10 days with the first bites, figuring if I could get it small enough they'd know it was food later on, it don't have the same smell that the first bites have, they were spitting i out the pellet and flake At first but it's still a little too big of a particle for them to work, they are starting to take to it, even if off the bottom later on when it's nice and saturated and soft after they fly through the first bites.

 

Hikari first bites didn't work on day 1 so I got nervous and quickly hatched brine shrimp eggs. Your tic tacs are about a week smaller than what I have. Funny thing is for over 10 years I could not parent raise angels because the parents ate the fry. This was my first successful batch and it happened at the office not at home! Imagine having to go to work Sat. and Sun. just to feed fish.
How long have you had the parents? Where did they come from? What do you feed them?

 

Im not familiar with Angel genetics, but a lot of heavily bred fish have recessive lethal alleles so having both of them will result in death...depending on what strains you have, maybe that's one possibility?

Good thought. Im not a fish genetics expert, but I have genetics experience in other animals and typically if you have a fatal recessive trait they would not have made it since November if they even survived at all. And considering basic Mendelian genetics only 25% of the fish would be affected. So much more likely to be a toxin. But I love the thought, because aquarium fish are full of genetic issues that you wouldn't see in nature.

 

Good thought. Im not a fish genetics expert, but I have genetics experience in other animals and typically if you have a fatal recessive trait they would not have made it since November if they even survived at all. And considering basic Mendelian genetics only 25% of the fish would be affected. So much more likely to be a toxin. But I love the thought, because aquarium fish are full of genetic issues that you wouldn't see in nature.

Fatal recessive genes are more common in this hobby due to inbreeding. One example I've seen is sailfin mollies. You cannot breed sailfin mollies with another sailfin molly. The homozygous combination of the allele is fatal, while the heterozygous combination is weak fish, ie can survive birth but will likely die later on. So in this case, not just 25% but 100% of the offsprings will be affected

 

Hikari first bites didn't work on day 1 so I got nervous and quickly hatched brine shrimp eggs. Your tic tacs are about a week smaller than what I have. Funny thing is for over 10 years I could not parent raise angels because the parents ate the fry. This was my first successful batch and it happened at the office not at home! Imagine having to go to work Sat. and Sun. just to feed fish.
How long have you had the parents? Where did they come from? What do you feed them?

Let's see... parents I had for about a year. They spawn every 12-15days if I removed the fry after being fryless. They started spawning just before Christmas for the first time. I got them from two different fish shops in different cities near me, one is a larger operation that does dogs cats and birds and the whole nine and family owned with a large fresh and salt operation, the other is a tiny hole in the wall private business that just does fish, and mostly freshwater. No guarantee the fish didn't come from the same place and might be related, im in south Florida and there's a lot of breeders and fish farms nearby down in Miami. but I did what I could without going to far to avoid it I think. I got 3 marbles from the big store and 2 calico/koi like patterns and 1 platinum from the small shop, stuck them together until two paired up the separated the other 4 which were males I believe since nobody lays eggs and they all get along fine.

This was my first successful batch also, I tried parent raising 3 times and jar rearing twice. The parents ate the eggs or wrigglers, and I had fungus issues first 3 times, I did the jar and methelene blue 1x and still got fungus, 1x with chlorinated tap water which I had no fungus but still had issues with the transfer to a tank at freeswimmers and those two attempts failed at day 1 of free swimming. This spawn popped up like 2 days after the last jar failure. I found a cloud of free swimmers with the parents a bit after valentines day which I'm figuring the eggs were laid around. I wasn't paying attention to them I was working on a batch in a jarthat failed, discouraged and then intended to give them a break and let them strengthen up so it came as a surprise. No idea if the eggs fungused or what but the parents apparently tended to it well enough this time so spawn #6 worked out.
They spawned again last Sunday and I removed the eggs on the slate this time, let my other fish eat them since I'm working with this batch and don't need more/can't handle more currently.

I tried with a different pair about 2 years prior to trying to get a pair. That pair never got past eggs and most turned white right away and the rest turned white before hatching to wrigglers. Just not a good match for viability.

And yeah, like I said, I feed first bites, past week I've added in finely ground up shrimp pellets and finely ground flake, both of which I have anyways but the first bite particles are so tiny, and it just take more and more of it to feed and the packs so small. so I'm trying to get them off it and to larger particles of dry foods. I could go to brine shrimp but this is just easier and they are eating it and growing and they'd need to be on flake and dry stuff at some point anyways.

 

Fatal recessive genes are more common in this hobby due to inbreeding. One example I've seen is sailfin mollies. You cannot breed sailfin mollies with another sailfin molly. The homozygous combination of the allele is fatal, while the heterozygous combination is weak fish, ie can survive birth but will likely die later on. So in this case, not just 25% but 100% of the offsprings will be affected

If you will pay attention to my description of basic medallion genetics you would know that im not talking about an incomplete penetrance or codominant situation, which would refer to a weaker subtype due to the heterozygous mix. With a basic genetic assortment we assume that the ones with the dominant alleles are getting only that expression. Therefore the recessive alleles are only expressed in the homozygous recessive population. Which would most likely not survive birth. Also to counter your point of "100% of the offspring would be affected" - only 75% would be under a normal assortment.

However you are correct that in reality there is much more complexity to the situation than just the basic assortment. But for the understanding of this thread it is much easier to assume the basics.

But if you would like to propose that all of his fish ie. 100% of his population now have a recessive gene then we can have the discussion. It would be incredible if in one generation he had a recessive allele move into complete fixation in a population. That is an awesome statistics problem that I would have to open the book to review the formulas for to see the chances. Being a small and limited population we obviously know that it doesn't fall under Hardy Weinberg and the chances of this happening go up significantly. What are the cases that this could happen if we consider the parents genetics and that the recessive combo is 100% fatal?

Assuming basic assortment:
Scenario 1
Parents: Aa, Aa
Offspring: 25% AA, 50% Aa, 25% aa (this group is dead)

Scenario 2:
Parents: AA, Aa
Offspring: 50%AA, 50%Aa

All "aa" scenarios can not happen because we established that is fatal.

So no we look at the population break down. In scenario 1 33% of the offspring were dominant and have no problem and 66% of the offspring have a recessive trait. In scenario 2 it is 50/50.

So now we could go back and consider an incomplete penetrance trait killing his angelfish. Are 66% of the fish affected and 33% fine? Remembering that incomplete penetrance is not going to look the same at each individual level.

What are your thoughts?

My thoughts is its a toxin in his tank.

 

If you will pay attention to my description of basic medallion genetics you would know that im not talking about an incomplete penetrance or codominant situation, which would refer to a weaker subtype due to the heterozygous mix. With a basic genetic assortment we assume that the ones with the dominant alleles are getting only that expression. Therefore the recessive alleles are only expressed in the homozygous recessive population. Which would most likely not survive birth. Also to counter your point of "100% of the offspring would be affected" - only 75% would be under a normal assortment.

However you are correct that in reality there is much more complexity to the situation than just the basic assortment. But for the understanding of this thread it is much easier to assume the basics.

But if you would like to propose that all of his fish ie. 100% of his population now have a recessive gene then we can have the discussion. It would be incredible if in one generation he had a recessive allele move into complete fixation in a population. That is an awesome statistics problem that I would have to open the book to review the formulas for to see the chances. Being a small and limited population we obviously know that it doesn't fall under Hardy Weinberg and the chances of this happening go up significantly. What are the cases that this could happen if we consider the parents genetics and that the recessive combo is 100% fatal?

Assuming basic assortment:
Scenario 1
Parents: Aa, Aa
Offspring: 25% AA, 50% Aa, 25% aa (this group is dead)

Scenario 2:
Parents: AA, Aa
Offspring: 50%AA, 50%Aa

All "aa" scenarios can not happen because we established that is fatal.

So no we look at the population break down. In scenario 1 33% of the offspring were dominant and have no problem and 66% of the offspring have a recessive trait. In scenario 2 it is 50/50.

So now we could go back and consider an incomplete penetrance trait killing his angelfish. Are 66% of the fish affected and 33% fine? Remembering that incomplete penetrance is not going to look the same at each individual level.

What are your thoughts?

My thoughts is its a toxin in his tank.

Hmm maybe 100% is not correct, I'm just going by word of mouth that sailfin mollie x sailfin mollies do not produce viable offspring. Im assuming incomplete dominance plays a significant role and possibly multiple alleles are involved.

A quick search led to this paper on lethal hybridizations in swordtails and the effects of heterozygous alleles: A Lethal Genetic Incompatibility between Naturally Hybridizing Species in Mitochondrial Complex I

Anyways, Im not ruling out toxins either, but I do believe the effects of genetics should be something to consider...Just purely from hobbyist gossip, I've heard traits like koi outside of goldfish are especially hard because of weak or non-viable offpsrings. Same with metallic colors, purple colors, pink colors and more in non-carp fish.....

 

Like I said I don't know fish genetics. I'm purely speculating on the basic possibilities under a general inheritance pattern for a recessive allele. Also why I stated "aquarium fish are full of genetic issues that you wouldn't see in nature." This is due to the ridiculous amount if inbreeding and hybrids. But the sailfin x sailfin combo sounds more like a hybrid breeding problem. Like breeding 2 ligers . You just cant do it because the genetics aren't compatible. But im not familiar with sailfins or other fish breeding in general.

Note on the purple or pink - are you referring the the GloFish colors? Because that is an entire other wonderful genetic discussion! Not an inbreeding case, but a gene editing case.

 

well, I'm no scientist, probably not very well spoken either.

my thoughts are "just the way it goes with angelfish and why they lay so many eggs".
from my limited experience, and I've got a extremely fundamental understanding of genetics, but as I see it, my angels are gonna lay like 500 eggs, and I might get to 300 wrigglers, and I might get to 200 free swimmers, and I might get to 120 pea sized, and 90 dime sized and 50 nickel to quarter sized (we will see how it goes from pea sized onward), but doesn't necessarily need to be genetics or toxins and just "how it is" and if you start with 40 free swimmers that make it that far and lose 1-2-3 a day, in a month you are out of fish. and this doesn't account for culling of belly sliders, or missing pectoral fins, or undersized gill plates, or a bunch of other conditions that could appear along the way.

they are sensitive to a lot of things, they have a lot to learn in order to survive. Then if too much water change at once it might change pH and shock them, a temp change might shock them when adding water, a food change might spook them from eating, a tank change might be off on something like hardness or phosphates or something nobody pays much attention to, or just the change of the environment and the move stresses and weakens them and they don't adjust, or then you have "failure to thrive", they just can't figure out how much they need to eat to grow and end up starving themselves as they get outcompeted by the others.

A toxin can explain a crash that kills them all quickly. Bad genetics could explain a low fry count, just as well as a male not being good at fertilizing eggs yet could explain a low fry count, or a female that has freshly matured, or a fungus taking over the spawn site and killing viable eggs and fry if not moved could explain a low fry count.
But the more you start with, the more you can likely get over the hump to nickel-quarter size I think but there's going to be a lot of deaths along the way. Starting with a few out of hundreds of eggs, the deck is stacked against them to make it to nickel-quarter in 3-4 months of growth and still be alive.

I posed the question to Google "How many angelfish fry make it to adulthood from a spawn" I don't get a straight forward answer to how many make it out of the hundreds of eggs laid, but I have to assume it's something like 10-20% that make the long haul. and maybe even lover and the breeders are working multiple pairs and volume to make their numbers. I think it's just another of the many secrets they all leave out of the youtube videos.

Actually I did find an answer but had to pose the question differently and learn a new word "Fecundity" and found a study. The average mortality rate of 20 females in this study, varying from 18-50 grams bodyweight fed three different diets 3x a day, by day 135 (4 month) is 33.8% for artemia, 43.8% for crushed flakes, and 50% for rotifiers. Still it was a laboratory environment, and they experienced a 96+% hatch rate from the spawnings also and very controlled water conditions. there was best growth from the artemia and about 1cm less size in the time period for flake.

Fecundity, growth, and survival of the angelfish Pterophyllum scalare (Perciformes: Cichlidae) under laboratory conditions.

anyways, I found it enlightening, the study on foods and growth and found the mortality rate to be higher by the 4 month mark than I had expected. the low spawners did just as well as far as eggs hatching as the big spawners, and all groups experienced similar mortalitiy rates over time.

I guess what I mean is, me being a novice at fish rearing, losing a lot of the spawn as eggs, there's just not enough left to then get hit by the 34-50% mortality rate by the 4 month mark after from larval onward. there's a big drop of 25% over the first 50 days and then a smaller drop of 10-25% more though day 135. I would suppose the high hatch rate regardless of spawn size is the key and food makes a difference too.

 

well, I'm no scientist, probably not very well spoken either.

my thoughts are "just the way it goes with angelfish and why they lay so many eggs".
from my limited experience, and I've got a extremely fundamental understanding of genetics, but as I see it, my angels are gonna lay like 500 eggs, and I might get to 300 wrigglers, and I might get to 200 free swimmers, and I might get to 120 pea sized, and 90 dime sized and 50 nickel to quarter sized (we will see how it goes from pea sized onward), but doesn't necessarily need to be genetics or toxins and just "how it is" and if you start with 40 free swimmers that make it that far and lose 1-2-3 a day, in a month you are out of fish. and this doesn't account for culling of belly sliders, or missing pectoral fins, or undersized gill plates, or a bunch of other conditions that could appear along the way.

they are sensitive to a lot of things, they have a lot to learn in order to survive. Then if too much water change at once it might change pH and shock them, a temp change might shock them when adding water, a food change might spook them from eating, a tank change might be off on something like hardness or phosphates or something nobody pays much attention to, or just the change of the environment and the move stresses and weakens them and they don't adjust, or then you have "failure to thrive", they just can't figure out how much they need to eat to grow and end up starving themselves as they get outcompeted by the others.

A toxin can explain a crash that kills them all quickly. Bad genetics could explain a low fry count, just as well as a male not being good at fertilizing eggs yet could explain a low fry count, or a female that has freshly matured, or a fungus taking over the spawn site and killing viable eggs and fry if not moved could explain a low fry count.
But the more you start with, the more you can likely get over the hump to nickel-quarter size I think but there's going to be a lot of deaths along the way. Starting with a few out of hundreds of eggs, the deck is stacked against them to make it to nickel-quarter in 3-4 months of growth and still be alive.

I posed the question to Google "How many angelfish fry make it to adulthood from a spawn" I don't get a straight forward answer to how many make it out of the hundreds of eggs laid, but I have to assume it's something like 10-20% that make the long haul. and maybe even lover and the breeders are working multiple pairs and volume to make their numbers. I think it's just another of the many secrets they all leave out of the youtube videos.

Honestly a fantastic down to earth summary of what is called Fitness! Definition: "quantitative representation of natural and sexual selection within evolutionary biology". Basically the strong survive and pass on these traits that made them survive.

 

Like I said I don't know fish genetics. I'm purely speculating on the basic possibilities under a general inheritance pattern for a recessive allele. Also why I stated "aquarium fish are full of genetic issues that you wouldn't see in nature." This is due to the ridiculous amount if inbreeding and hybrids. But the sailfin x sailfin combo sounds more like a hybrid breeding problem. Like breeding 2 ligers . You just cant do it because the genetics aren't compatible. But im not familiar with sailfins or other fish breeding in general.

Note on the purple or pink - are you referring the the GloFish colors? Because that is an entire other wonderful genetic discussion! Not an inbreeding case, but a gene editing case.

No Im talking about the color purple/pink in common ornamental fish like bettas, angelfish, guppies etc, which breeders have tried to achieve but proved to be very difficult. Afaik, part of the difficulty is there is no purple/pink gene in those species, and those that are somewhat purple/pink have reduced lifespans and prone to cancer

 

And now for something completely different.
Could it be dietary?
They all had voracious appetites the day before they stopped eating. They picked at everything from BBA on the sponges, slime on a filter, all kinds of flake. Something in their dietary intake that had an accumulative effect or bacterial impact on digestion?
The genetics is very interesting and thought provoking but strays from Occam's Razor. However, don't stop posting, your analysis keeps me tuned in. I had thought all the intelligent people had left the planet, these ideas, theories, postulations and references give me hope. Thank you.

 

And now for something completely different.
Could it be dietary?
They all had voracious appetites the day before they stopped eating. They picked at everything from BBA on the sponges, slime on a filter, all kinds of flake. Something in their dietary intake that had an accumulative effect or bacterial impact on digestion?
The genetics is very interesting and thought provoking but strays from Occam's Razor. However, don't stop posting, your analysis keeps me tuned in. I had thought all the intelligent people had left the planet, these ideas, theories, postulations and references give me hope. Thank you.

If they ate something poisonous then Id say that falls under toxins... most things in a fish tank ie bba, biofilm are not poisonous so I don't think it's due to natural food.