Mandarin dragonet spawning log

[DaJMasta]

Exciting times in the tank, in the last month my pair of mandarins (both wild caught and both eating frozen food) started spawning!  I haven't gotten very far in the process yet, but they spawn about every other day in bursts, a few days consecutively, then a few days off, so I want to start documenting it.

 

So far, the larva have lived to 24 hours, and while not long, this actually represents a couple weeks of attempts which ended up being something very silly.  When collected, the eggs are almost entirely clear, and are a little smaller than 1mm in diameter.  Each spawn I've seen is 2-4 dozen eggs, or so, and while the flick of the tail at the end of the spawning spreads the eggs around, some of them do seem to stick together in a two-wide string.  They usually spawn just after the lights dim to the moonlight stage, so between 10 and 11pm, and it's easiest to tell if they will because the female of the pair will just go to sleep if they're not!  When they do, there's a few minutes of sort of chasing each other in one area, then they ascend towards the top of the tank, swim right next to each other, and flick their tail and run away, releasing the eggs at the same moment.  The first spawns I caught were actually when the tail flick broke the surface and made a splash sound, though there have been a couple of times where they haven't ascended very far in the tank to spawn.

 

The eggs look like this, and are easiest to spot with side lighting and the pumps off:

(one is to the far left in the center, there are a few in the 10mL beaker)

 

Within a couple hours, the fertilized eggs are already growing and show a sort of cleft in their internal structure

(the lines on the right are actually copepod legs, if I remember right)

 

The eggs take about 12 hours to mature - at the 11 hour mark I've seen no evidence of larvae, but at 12-13 hours I do.  Unlike the eggs we usually think of, the outside of the egg just becomes the outside of the larva, so it's more like a bare embryo.  They sprout a tail and an eyespot, have a slightly green color, and look like this:

(a little bit of blue fiber for one of the more in focus moments)

 

It was at this point that I lost several clutches worth of larvae for no apparent reason.  They would hatch, react to light, and then disappear over the course of about 4 hours despite good water parameters.  Well, after reading another breeding attempt account that mentioned the eggs were about 0.8mm in diameter, it clicked...  I had kept the eggs in my kreisels, which use a 500 micron (0.5mm) mesh on the sides... so they were turning into larvae and then just swimming off into the tank through the mesh where they encountered higher flow and hungry fry mouths.

So with last night's spawn (small, maybe only a dozen or so eggs collected), I put the eggs in a 200 micron mesh strainer in the top of the kreisel to be emptied after a bit, and lo and behold, I have 24 hour old larvae.

 

So 12 hours after being an egg, the larvae already have a few lobes worth of shape, a distinctive head shape (though only a central eyespot), and a relatively developed tail for what is basically a tiny blob.

According to other accounts, they should grow for another two days without any digestive tract, then around day 3-4, they turn a pale yellow and start eating.  They will be tiny and will need tiny food, and while I've still been having trouble getting more variety in copepod species for food, I've started sorting them by size for feeding (hopefully to help the lysmata shrimp attempts as well), so I can sieve out the nauplii of the pods I have (apocyclops, primarily) so that the food offered is something they can actually fit in their little mouths.

[AlanM]

Wow, what all do you have spawning? 

 

I think you have banggai cardinals, porcelain crabs, and mandarin all spawning?

 

You're definitely the happiest tank in WAMAS at this point, I'd say.

[DaJMasta]

Skunk cleaner shrimp too!

While I do think the moving animals are happy, I think the corals are really only just starting to act totally happy, and I think a lot of it is just paying close attention.  It's a nightly ritual at this point to turn the pumps off at 10pm, get out a camera that can see a bit better than me as sort of closed circuit TV, and then take a look every few minutes with the flashlight.  I've caught a handful of spawns which I just can't identify yet, too, but there's a good chance it's some kind of small animal I don't even know is in there...

[DaJMasta]

On day three, I didn't see the one larvae that I had gotten a picture of before.  I had only collected maybe 10 or so eggs from that smaller spawn, and there was a chance I had hurt it by pulling it out for the picture (though I try to limit handling and time under the microscope and it moved normally when returned), but the problem ultimately was something else.  When I pulled up the tape holding the folded mesh in place I had for it, I found a fold behind what I could see that opened underwater, so I think it, like the others before it, escaped into the tank.

That was from a spawn Friday, and they didn't spawn again... until this evening.  Apparently there was a good reason for the wait:

 

I probably collected more than 200 eggs from this evening's spawn, and I had designed and was already printing this holder that fits in the top of the kreisels I've got at the time the last spawn escaped.  The timer resets again, I have no idea how many may hatch, and I still haven't gotten any to the stage where they can eat... but I've got another attempt in progress!

[DaJMasta]

13 hours post spawn (larvae started not looking like eggs around the 12.5h mark):

 

This evening, 25 hours after spawn, you can see the sort of bulbous tadpole shape in the form still, but you can see the much wider tail with a central part, and sort of two primary body areas:

 

Then very much to my surprise, I found another few dozen eggs in the tank this evening - they are certainly prolific spawners.

[AlanM]

Wonder if Matt Pederson would be interested in talking to you about any of these spawning events and your work to raise them and print parts to harvest the eggs and such.  He's the editor of Coral, a former WAMAS speaker, and all around nice guy.

[DaJMasta]

I'd be happy to talk about my methods, but it's probably better to get a bit of success before I go recommending anything!  Of course, with the amount of stuff spawning, I'm hoping it's more a matter of time than ability.

 

This morning marks the new high-water mark in terms of success, since they haven't escaped!  37 hours post spawn:

 

And under the microscope:

 

They have a distinctive clear tail section, a much longer central body, and the beginnings of a spinal cord or maybe digestive tract down the middle.  Still have the bulb of yolk that will carry them through to when they can eat something.

I'm trying to document every 12 hours worth of development, as they're almost different organisms in such short intervals, but will move to daily and then longer intervals once they can eat.  I look forward to seeing them grow!

[DaJMasta]

In the last 12 hours, they developed eyes and even tiny pectoral fins.  The development rate of these larvae (apparently prolarvae before they can eat) is incredible.

[DaJMasta]

This morning, 2.5 days in, they looked similar to last night but were acting distinctly more like fish and less like larvae.  Before they mostly drifted with the occasional burst of speed that sometimes turned them sideways or over, but now they seem to maintain themselves more upright, move in a more coordinated fashion, and move with smaller bursts of energy (at least most of the time).  You can see their eyes are more clearly developed and maybe are closer to the surface of their skin, and those tiny pectoral fins have doubled in size.

 

I knew they were slowly coming up on being able to eat, so mid day I had a look.... and I saw something on video which was basically imperceptible by eye:

An enormous (for their size) mouth!  The light in the tank even occasionally caught and lit up their eyes.  So I went and fed them, using a pair of sieves on my apocyclops cultures.  I used a 45 micron sieve to collect everything, and a 300 micron sieve to screen out the adults - and larger and stronger ones got through than I thought, so for the next feeding I went with a 45 micron and a 200 micron.  I can't tell exactly how successfully they are eating, but I see mouths opening and little charges at things, though I haven't yet seen all that coordinated of a strike.

This evening, 3 days after their conception, they have mouths, use their pectoral fins for movement like their parents, have pupils in their eyes, and are at least trying to eat!

 

And though in motion... that mouth is really something for the size of the critter

 

Edited March 6, 2022 by DaJMasta

[DaJMasta]

The little guys seem to be doing well, at least so far as I can tell, but I'm not sure if they're eating as well as they could.  They still aren't particularly efficient hunters, but they do seem to be prowling around and there are a lot of pods around to eat.  There appear to be fewer of them, but they could also just be more spread out - before they were mostly towards the top, and now I'm seeing some scooting around a bit on the mesh at the bottom of the box, so it's difficult to get a good count.

Somehow their mouths look even bigger today, and their head looks wider, though they appear more slender which may not be a good sign.  Their eyes seem more developed - very clear pupils but not really tracking around - and their movements are more like the adults, just vibrating their pectoral fins (which are a little longer) and the tip of their tail, not nearly as much full-body thrash which characterized their early movement.  Their jaw seems put together like a fish with a big gulping mouth, as they can probably almost fit something the size of their head into their mouth, and their relatively simple looking digestive tract is apparent.  One nice thing, I saw some movement in the belly of one of the fish under the microscope - and from the kind of movement and area, I don't think it was just internal organs.  So while their feeding (mouth opening) behavior has increased today, it looks like at least some of them are having some success.

Look at that mouth!

 

Underside showing the jaw, a bit of the skull, and the shape of the digestive tract.

 

Big head, little body.  Hopefully not because it's not able to eat enough.

[ScooterTDI]

This is great work! What are your approximately prey densities in the larval tank? Do you have any parvocalanus cultures going? I found the parvo cultures to be way more productive than apocyclops. 

[DaJMasta]

I don't have an appropriate metric - I haven't done any counts - but I've been taking about a quart out of my 2 gallon culture vessel, running it through a coarse and fine sieve down to about 1/4-1/3 of a cup, then taken maybe 3 pipettes full to feed the ~2 cup vessel.  My best approximation is just a visible one, and there are quite a few:

(the big blob is one of the baby mandarins, all the dots are pods).

 

In the maybe 8-10 drops of water I caught today's fry in to examine under the microscope, there were probably a dozen or so copepods in their earlier larval stages.

 

Now the not so great news, and some of it is visible in the above pictures.  In the last day and a half or so, I've lost something like 80-90% of the fry.  Exact causes are unknown, but I have a strong suspicion that it's diet, or lack thereof, and I think the body shape comparison between the one from yesterday and the one from today are a good example of how dramatic it can be.

 

So while I was seeing lots of mouth movement, even early on, it seems they had trouble getting the nutrition they needed to keep growing, and I think there's three potential - one probably the biggest - problems that they faced.

 

Prey size: while only once, I used a coarser 300um mesh for the first feeding, so some larger apocyclops were introduced early on and still are visibly there now - some large enough to be full adults and not be something the fry could swallow.  While the minority of the food available, I think their presence could trigger a feeding response that just results in wasted energy, something at a premium when learning to eat.  Future runs will be all 200um mesh as that appears to be a more appropriate size, though I will probably get some 250um mesh to check and see what gets through.

 

Second would be nutritional value: copepods are generally considered to be pretty nutritious, but it could be that the algae I'm feeding them isn't the right mix to support new critters.  I'm feeding the copepods isochrysis and tetraselmis right now, and two good quality phyto strains is considered generally good, but I've started culturing diatoms - chaetoceros and thalassosira - with the hopes of mixing them in to enrich the copepods further, and also to introduce to early larval stages to stimulate eating (I read one study rearing Lysmata shrimp where introducing diatoms in the first 24 hours promoted digestive juices, even though the larvae didn't seem to be able to use it for food on its own).  It's a week or so out from being introduced to my culture feed, so we'll see how it goes.

The third, and probably most important: that the prey is probably too hard for larvae to catch.  Given the uncoordinated feeding response of the new fry and the lack of success with some other organisms, I think apocyclops nauplii and juveniles may just be more difficult to catch than other feeds.  I especially get this impression with accounts of people with similar conditions raising larvae successful on artemia nauplii, which are considered less nutritious than copepods, generally.  I think this is one of the big benefits of parvocalanus, but it's not a copepod I've been able to successfully culture yet.

 

So for this last approach there's probably most room for improvement, but like with the diatoms, I've got stuff in the works.  I've got a tigriopus culture to a little more than half volume that I will try to see if they are viable as a new fry food source - while the adults get bigger and I think the nauplii start larger, if they are small enough and easy to catch, it could be a viable option and the culture seems like it will be similar maintenance to my existing ones.  I've also got a portion of parvocalanus and pseudodiaptomus on the way - both of which I've attempted to culture unsuccessfully before.  This time, I will be much more careful about food density - I think I may have sort of extinguished previous cultures by dosing too much phyto too early and maintaining a problematic density for the early cultures, but I will look for some papers to get ideas of what to improve on before they arrive, and I'm hoping the diatoms will help out with them as well.


At the end of today, I have maybe a half dozen of the fry from the batch pictured, but they seem to be better hunters and seem to be eating and not looking thin.  Since the mandarins spawned two consecutive days after this big spawn (and then not since!), I actually collected those eggs and put them all in a sieve just clamped to the side of the tank, and I'm seeing a good number of larvae in there too which I'll transfer over to be with this batch in the next few days.

[TrueTricia]

This is incredible!!!  I am a huge fan of captive breeding, and I love that we have someone within our community willing to put in such work, learning how to do things better, and sharing that information with our community.  

[ScooterTDI]

Yea, in my experience parvo is sensitive to water quality and algal density. When I was culturing them, I had the most success feeding very lightly twice a day and I would immediately sieve and restart the culture with a fresh batch of water if productivity declined. Usually, restarting the culture resulted in a substantial bloom. I probably restarted parvo cultures once a week. If I remember correctly, I was able to reliably harvest about 25% of the culture volume every day, so they cultures basically got a 25% water change daily.

[DaJMasta]

Interesting, I had heard that restarting without adults was important to keep them from eating their young, but had assumed that you could maintain a lower culture density by just doing the remove and replace a chunk each day.  Will have to change the routine up a bit, as my cultures are usually getting about 10-15% changes a day, but I think my algae feed is dense enough that a 25% change in volume a day with new algae wouldn't all get eaten, so maybe a combo of phyto and new saltwater, but I'll have to see.

 

The first hurdle will be just growing the 16oz into a 2 gallon culture, and I will focus on daily volume increases while making sure only to tint the water somewhat so that it's clearer looking than other cultures.

In the meantime, while I think the tigriopus are slower growers, I think my culture will be grown in by the end of the week, and they seem to have no problem with fairly high food density and use a lot less aeration.

Will get proper pictures tonight, but I've still got at least one of the original batch of fry, and it's basically eating continuously, so it looks like apocyclops will probably do once they've figured out how to hunt, and there are maybe a dozen of the group that's 1-2 days younger from later spawns.  I've also read that just having multiple strains of copepod increases feeding response and nutritional content with some other larval species, so hopefully being able to reliably offer at least two kinds will help increase the survival rate.

[ScooterTDI]

I don't think parvo are cannibalistic like some other calanoids. I never had any problem restarting cultures with sieving that retained adults. Make sure to feed VERY light. I would put my clear 1g culture vessels up against a white wall and if I could perceive any tint to the water I would not feed. I only fed enough that I could see a slight tint when against a white backdrop. It would normally look totally clear if it wasn't against a white backdrop. If the tint doesn't dissipate by the next feeding, the culture was usually due for a restart. Also keep the aeration very light at only maybe 1 bubble/sec.

 

There is a good chance apocyclops alone will work, but I could never reliably maintain high production with them. I suspect Tigriopis won't work well. I tried them unsuccessfully with blue stripe pipefish a long time ago and I think they have a larger gape than mandarins. Good to have those around after settlement though.

 

I'm keeping my fingers crossed for that last survivor from the original batch!!!

[DaJMasta]

I wouldn't be surprised if all of them are cannibalistic to some degree, but I will try to be sparing with my feeding of the next batch of parvocalanus and see how I can fare - the low airflow is a good tip too.

 

For the apocyclops, I take completely the opposite approach, as high aeration levels as I would use with phytoplankton, and for a 2 gallon culture, I remove a quart to feed and then replace it with phyto, same density it was harvested at, which is mostly opaque.  The culture will be back to almost clear the day after around the same time.

At 6 days old, this little guy is still going strong:

 

And when he opens his mouth all the way, you can see straight through to his under eye!  Today the sort of big mouth structure finally starts to become clearer - not just a giant mouth, but a big mouth interior and not necessarily a huge gape, since it's got clear membranes surrounding most of the jaw, so they have sort of a reverse bellows to suck in water and prey.

 

Speaking of sucking in prey.... he is eating

 

[AlanM]

Neat to see him kind of chewing on it a bit after getting it in the mouth.

[ScooterTDI]

Maybe that was my problem with apocyclops.... I aerated them only slightly more than the parvo.

[YHSublime]

So, mandarin larvae are like the bulldogs of the canine world? Huge jaws, but harmless? 

 

All jokes aside, this is phenomenal, especially in a home setting. I was planning on ordering a pair from Biota, but have been unsure if my tank was too aggressive for them, I hear they are small. I'd much rather support your endeavors and research if you'd consider selling them when and if they get large enough. 

 

Until then, tagging along, kudos to you for having the patience. I looked into clownfish breeding, and the reading alone exhausted me! 

[DaJMasta]

Looks like their massive jaws are the beginning of the big part of their adult vacuum mouth, and their skin around it is just just so transparent it's hard to tell they don't have a giant deep sea anglerfish sort of mouth.

 

Some sad but not entirely unexpected news, I seem to have lost the last guy from this batch overnight - I did not see him today.  While he was not free swimming as much yesterday and didn't seem to have a ton of energy when caught and examined, he did eat on camera, which gave me some hope.  I think when larvae start swimming around on the bottom of the vessel instead of in the water column, it's probably a sign of lack of nutrition.  There's also a chance my removing one from the vessel and looking at it under the microscope was a problem (5-15 mins out of the main tank probably cools the water a couple degrees and there could be a handling issue with using a pipette to suck them up), but I expect there will be less handling done this time as the early stages don't need so much extra documentation.  Perhaps because of the first feeding using a larger screen, some of the apocyclops seen in the vessel with that last guy today were full sized, egg bearing adults, and especially if they are difficult to catch, I need to delay feeding to only when they can eat and then be sure to use the finest sizes only to be sure the growth rate of the food copepods doesn't outpace what the fry can eat!

 

While this first semi-success of a run ends here, the parents are still prolific spawners, and while they had several days off, yesterday and again today they spawned.  The eggs collected yesterday were put in the same vessel as the last guy, and we will see if they can survive among a dense copepod population (pods bumping into them may mean they use a lot of energy just jumping out of the way), but the eggs collected this evening were put in a newly started vessel.

 

To try and improve on the method while new food options start to get spun up, I will:

Add no food until 3 days post spawn

Add only food that fits through a 200um screen

Add some tigriopus nauplii, provided they fit through the right screen, once a day as that culture starts to get going

Feed twice a day in quantity

 

I should have new copepod species at the end of the week to start new cultures, but they will be weeks out from production ready provided I can keep them going.  I'm starting to get the diatoms online, so I'm running some tests already to make sure the pods I have can eat it, and when I can verify that, diatoms will be added to the phyto mix I'm feeding them to hopefully enrich the diet and make them a more nutritious food.

A thought that occurred to me today but which I couldn't find real evidence for or against - I wonder if they need some amount of lighting to hunt.  It seems like with the well developed eyes and the reaction I saw, they are hunting by sight, so I wonder if there is a maximum or minimum lighting (within reasonable amounts) where they can be successful.  The larvae never seemed to be bothered by being in the light or being in the shade, and I have moonlights that run a dim light all night, but maybe there's some room for optimization there too.

[ScooterTDI]

You should definitely play with the light intensity and extend the photoperiod. It also helps if the sides of the vessel are black for better contrast with copepods.

[DaJMasta]

The mesh is whitish, but the sides of the little vessels I keep these prolarvae and early larva in (at least until they can't get through the screen of the larger kreisel) are black, so it's basically only top lit except for when taking pictures.  I could experiment with turning up the overhead light, but I had it low so it wouldn't draw things to it/force things into the shade too strongly and to discourage random algae buildup.

 

A small update:
There are still larvae in the batch collected on the evening of the 8th (3 days old now), and even though there are lots of apocyclops buzzing around in there, them being bumped into doesn't seem to be that detrimental to their development.  It may still make it harder to find small enough food when they can eat, but it's at least feasible to do several consecutive days of spawn in a single tub.

I fed those larvae from the 8th today with my first harvested batch of tigriopus - the density is reasonable but will probably increase and the adults are notably larger, but I do see just a little bit of movement in the <200um screened portion.  There was a bunch of algae detrius, since this came off the bottom of the new culture which was growing out for like three weeks, but the few nauplii I saw in there moved MUCH slower than the apocyclops young, so if I can produce them in enough quantity, they will probably work as a food source for these larvae.  Maybe not for critters that have even smaller mouths, but a mouth the size of your head has its advantages.  I want to try a 250 micron screen as well, but while I have some 250um bags on order to cut up, they haven't arrived yet so I'm at least a couple days out from being able to try.  Hopefully as the culture matures and the sediment gets out of the bottom I'll see more nauplii of a suitable size for these little mouths.

Otherwise, the batch collected on the 9th which will get the full "new" approach outlined in the last post, they get their first feeding on the evening of the 12th, and I've got half a dozen or more that seem to be acting normally.

[DaJMasta]

A whole series of changes in a short update:

I fed the larva from the 9th this morning.  I had a look on the camera (enough magnification to get a good view that really is tough by eye) and their behavior looked distinctly more like hunting and less like the pulses to keep in the water column of the night before, so instead of waiting to the 3 day mark, I fed them at 2.5 days, and I fed them with sieved tigriopus.  I then fed them mid day with another small portion, but used the 300um sieve - more got through, definitely some too large to eat, but I don't yet know if it's a problematic size.  Then in the evening they got their first dose of apocyclops, but I foolishly used the 300um sieve instead of the intended 200um sieve, so there are larger and stronger swimming pods in there than I had intended.

 

Probably related, I didn't see any larvae in the batch from the 8th that seemed like they were doing well.  My guess is the larger pods all around weren't a problem as prolarvae, but as soon as they could eat, they made it tough for them to find appropriate food, and just ran themselves out of energy.  Not what I was expecting day 3 -> 4, but I think fairly conclusive evidence that prey size being small enough is essential for these new larvae.

 

Tomorrow, then, will be the check to see if the tigriopus pods and the larger sieve apocyclops are too big for them to eat - as that's when everyone in the previous batch disappeared.  I'm hoping that the easier to catch tigriopus help them along in these early stages, but only time will tell.

 

I've also decided to leave a light on the batch now, to see if it helps them find their prey.  It's not terribly bright, but it is close, so it's a reasonable brightness, but it appears that having a light on helps keep them near the surface instead of elsewhere in the vessel, and the copepods generally are attracted to it too, so there could be a couple of potential benefits.  There was lighting and an always-on moonlight before, but now the brightness is up, and at least until their eyes are more developed, that could certainly help.

 

My 250um screen apparently hasn't shipped yet, even though it's been paid for for a week, so I'm a way off of being able to try that size for pod collection, and while pseudodiaptomus and parvocalanus pods arrived on Friday, either losses in shipping or salinity shock in adding the new water to start the cultures really did a number on both - I'm counting less than a dozen individuals in each..... but there are some, and they're at my normal salinity for cultures (30ppt) and have a very light tint of isochrysis, so while it will take longer, I hope that they will grow out in the coming weeks.

[DaJMasta]

With more spawns come more attempts!  The previous batch lived a bit longer, another half day, but without any notable points of success.

 

3 days ago I got another spawn, followed by one two days ago and one yesterday, so while I don't have proper cultures of new pods going yet, I figure I will try when eggs are available and changes can be made.

 

The big thing this time is food timing - since the earlier prolarvae didn't seem to be bothered by even full sized copepods and I was already seeing a feeding response when fed at 2.5 days.... why not feed them earlier?  While I don't see clear hunting behavior or attempts at 48 hours post spawn, I fed this batch then with the hopes that between 2 days and 2.5 days, they would get some hunting practice and be able to eat something.

I've also got chaetoceros gracilis (a diatom) mixed in with the tetraselmis and isochrysis, which will hopefully round out the nutrient profile of the foods better and make any successful catch count for more in their development.  The tigriopus culture is up and running fine, so while once a day (1 culture vs. 3 of apocyclops), they'll also be getting mixed prey, all screened through 200um sieves.

 

While I don't know if it will remain on, I've also added some lighting for my own camera that I've been leaving on since starting to feed.  While I don't know if it helps them hunt, they do seem to hang around the surface more, which is probably preferable to on the bottom.

 

And because there's not a ton of culturing space, I've put eggs from three consecutive days into the same vessel, plus apparently a few sexy shrimp larvae from the day prior, so I've got quite a variety of creatures getting the same basic feeding and treatment.

 

So this morning is 2.5/1.5/0.5 days into a run, we'll see how it sorts out.