Mysid Shrimp Swarm?

[Jac647]

I have a 6 month old nano 20g reef tank. On two occasions, shortly after lights out I’ve gone to the tank and seen an absolute swarm (thousands) of insects swimming around. The first time I thought they were pods but upon closer inspection are these mysid or some kind of shrimp? How could the population get this big and is there a downside?

Managed to snag one for the microscope, video and picture attached!

 

[ISpeakForTheSeas]

I have a 6 month old nano 20g reef tank. On two occasions, shortly after lights out I’ve gone to the tank and seen an absolute swarm (thousands) of insects swimming around. The first time I thought they were pods but upon closer inspection are these mysid or some kind of shrimp? How could the population get this big and is there a downside?

Managed to snag one for the microscope, video and picture attached!

Any chance you've got hermit crabs in your tank? If so, I'd assume those are the larvae from them.

Edit: Let me rephrase that and correct myself; I don't see the rostrum typical of hermit crab larvae, so what crustaceans do you have in the tank (shrimp, hermits, crabs, etc.)? It's possible it's mysis, but I'd like to explore/rule out other options as well.

 

[Jac647]

Any chance you've got hermit crabs in your tank? If so, I'd assume those are the larvae from them.

Edit: Let me rephrase that and correct myself; I don't see the rostrum typical of hermit crab larvae, so what crustaceans do you have in the tank (shrimp, hermits, crabs, etc.)? It's possible it's mysis, but I'd like to explore/rule out other options as well.

No hermits!

I’ve got:
- 2 skunk shrimp
- 1 emerald crab
- 1 pompom (I think I got this one after seeing the “swarm”)
- 1 tiger conch
- various snails (turbo, astrea, nass, cerith)

There don’t seem to be a lot of pictures of skunk shrimp larvae, but I did find one and it looks like that could be it from my microscope picture? If that’s the case, do these have a chance of survival/growth or is this just a monthly feeding frenzy for the rest of the tank inhabitants?

 

[ISpeakForTheSeas]

There don’t seem to be a lot of pictures of skunk shrimp larvae, but I did find one and it looks like that could be it from my microscope picture? If that’s the case, do these have a chance of survival/growth or is this just a monthly feeding frenzy for the rest of the tank inhabitants?

Yeah, I'd say Skunk Cleaner larvae - for comparison:

https://upload.wikimedia.org/wikipedia/commons/c/ce/Lysmata_amboinensis_zoea_1.jpg

The chances of even one of them surviving are astronomically low - it happens sometimes, but it's not at all common.

If you want to try and rear them in a separate tank:

You may be able to find the diagrams of the development in the paper linked below, but it's behind a paywall:

Description of the complete larval development of Lysmata amboinensis (De Man) (Decapoda: Lysmatidae) reared under laboratory conditions - PubMed

Complete larval morphological descriptions are currently only known for three of the 48 species of genus Lysmata. The present study describes and illustrates the larval development of Lysmata amboinensis (De Man) reared under laboratory conditions. Lysmata amboinensis larval development is...

pubmed.ncbi.nlm.nih.gov

https://www.biotaxa.org/Zootaxa/article/view/zootaxa.5099.5.1

For breeding them:

If the larvae are in a normal reef tank, they'll die. Survivors in cases like this do happen occasionally, but the odds are ridiculously low - given that skunk cleaner larvae remain pelagic for 3-5 months, their odds are essentially nonexistent.

To rear these guys, you'll need a larval rearing tank and some live foods: Artemia (brine shrimp), rotifers, and phytoplankton together will give the best survival results, but only the Artemia (and phyto to culture them with) are necessary.

For a really simple larval rearing setup, see the thread below:

Breeding Palaemon Elegans (Mediterrane Rock Pool Shrimp) Guide

Hi, Im going to post a breeding guide of palaemon elegans shrimps here. Two females are preparing for spawning so if you are interested you may want to stick with me. This breeding guide will be interchangable for every kind of shrimps but i stick elegans because: - With cleaner shrimp we are...

www.reef2reef.com

For the complicated methods that might yield slightly better results (chapters 5 and 6 are the important ones for larval rearing purposes):

https://researchonline.jcu.edu.au/40038/1/40038-tziouveli-2011-thesis.pdf

Supporting info for the feeding:

https://www.researchgate.net/publication/230709198_Experimental_studies_on_the_effect_of_food_in_early_larvae_of_the_cleaner_shrimp_Lysmata_amboinensis_De_Mann_1888_Decapoda_Caridea_Hippolytidae

https://www.tandfonline.com/doi/abs/10.1080/10454438.2021.1986193

Some general aquaculture tips/info (it's oriented for fish, but a pretty much all of it is applicable to inverts - including shrimp - too):

If you've got questions on other species (such as the Fire Shrimp, Lysmata debelius), then I'm happy to help where I can.

(The below is general aquaculture info geared toward fish, but most of it's adaptable for inverts like shrimp too.)

______________________________________________________________________________________
General Summary:

Anyway, that's my species specific advice for this, now here's my general advice.


A quick summary:

-Setup a little, simple tank.
(The larval rearing tank).

-Add the larvae.

-Add the larval food and enough phytoplankton to tint the water green.
(The phytoplankton helps dim the lighting so it's not too bright for sensitive larvae, it makes it easier for the larvae to see the feeders, and it gut-loads the feeders so they're more nutritious when eaten).

-Adjust feeding as needed as the larvae grow; you typically should start feeding regular fish food in addition to the larval food around settlement.


Now the details - sorry, it's still a bit disorderly (I'm working on it).
______________________________________________________________________________________
Larval Rearing Tank:

The larval rearing tank should be setup prior to the eggs hatching if possible, and you should be prepared to move the eggs/larvae into it. Ideally, you'd be able to move the eggs into the larval rearing tank immediately before they hatch, but - if you don't know exactly when they'll hatch or if they've already hatched - you can also collect the larvae after they hatch and move them into the larval rearing tank (sorry, I haven't written up about larval collection methods yet - I'll probably get around to it eventually).

Anyway, for a simple larval rearing tank, all you need is:

-A small tank filled with saltwater (kreisel tanks are ideal, but not necessary)

-An airline/air stone/gentle sponge filter (for flow/oxygenation)


Depending on individual circumstances, you may also need:

-A heater (or chiller, though these would rarely be needed for anything other than temperate/coldwater species; these should be sectioned off from the larvae - such as with a 40 micron or smaller mesh - to prevent injuries to the larvae and to keep the feeders where the larvae can get to them)

-Light(s)*


You don't want standard tank filters, skimmers, uncovered pumps/powerheads etc. - those are not pelagic larvae safe.

The size of the larval rearing tank may vary depending of the species you're working with, but, generally speaking, you want it to be pretty small so you can easily keep the proper densities of feeders and phytoplankton.

For an example of a simple larval rearing setup:

Breeding Palaemon Elegans (Mediterrane Rock Pool Shrimp) Guide

Hi, Im going to post a breeding guide of palaemon elegans shrimps here. Two females are preparing for spawning so if you are interested you may want to stick with me. This breeding guide will be interchangable for every kind of shrimps but i stick elegans because: - With cleaner shrimp we are...

www.reef2reef.com

*A quick note on lighting for the larval rearing tank:
Some species require lighting, others don't; running a light that's bright enough to ensure the larvae can clearly see the feeders in the tank without being overly bright is generally a safe option. A 12 light:12 dark or 14 light:10 dark lighting schedule is generally suggested; some people also run dim "night lights" in the room away from the tank for the larvae.

If you see larvae headbutting the wall of the tank, that's a sign the light is reflecting off the tank wall and attracting the larvae, causing "head-butting syndrome" where the larvae ram into the wall often until they die - if you see this, you'll need to blackout the tank, but I haven't seen this be a big issue for most people, especially not when they're using the "green-water" method and tinting the larval rearing tank's water green with phytoplankton.
______________________________________________________________________________________
Feeding:

Much like human babies need special foods, larval fish also need special foods to survive. For larval fish, those foods (which I'll refer to generally as "feeders" after this) are things like live rotifers, Artemia (Brine Shrimp), and copepods, but each species of fish has specific food needs. Most larval fish need their feeders to move in specific ways in order to entice them to eat, so live food is typically a must.

As a note, some larval fish hatch with a yolk sac that they feed off of, but the yolk usually only lasts about two days - after those two days, the larvae need feeders or they'll starve.


Anyway, for a feeder to be useful in the rearing of larval fish, they need to:

-Be the right size for the fish to eat

-Be enticing to the fish

-Meet the larvae's nutritional needs at the time they're offered to them

-Be offered in the right quantity and density (for example, when rearing Ocellaris Clownfish using rotifers, the ideal density of rotifers for rearing the larvae is ~10 rotifers per mL, but you can't just put the larvae in a 1 mL tube and expect it to have enough food to eat; you need a reasonable density in a reasonably sized tank - also, some species [such as some cuttlefish, which are actually invertebrates rather than fish] may not eat if the feeder density is too high; so too low of quantity/density, and the fish starve, but also too high of density and they may starve)


In addition to these requirements, you (the aquarist attempting to rear the larvae) must be able to supply enough of the required feeders consistently throughout the duration for which they may be needed - this typically means that you will need to be culturing the feeders (and the phytoplankton needed to culture them) yourself to ensure that you always have enough of them on hand.

A lot of people run into feeder issues their first few times breeding, so having a backup plan in place to ensure that you can quickly obtain more of the right feeders (or their needed phytoplankton) quickly in an emergency is also a good idea.

Typically, feeders are best when gut-loaded (i.e. fed something - typically phytoplankton - immediately before they're offered to/eaten by the larvae) - the green-water rearing method (i.e. where the water in the larval rearing tank is tinted green with phytoplankton) is generally a useful, easy way to gut-load the feeders.

Now, to discuss more about the points above.


The right size feeders:
-Larval fish can typically only eat feeders that are approximately 20% of the size of their gape; this means that the smaller the larval fish are, the smaller their feeders need to be. To say it another way, if the feeder is too big, the fish can't eat it.

-Some feeders are the right size at specific life stages, but not at others, so you may frequently need to sieve the feeders to ensure you're offering the fish the right size of feeders.


An example to help explain sieving:

Adult Parvocalanus crassirostris copepods get up to 400 microns, whereas stage 1 Parvocalanus nauplii are about 40 microns. This means that the Parvocalanus nauplii should be ~1/10 the size of the adult pods - the stage 1 nauplii are a good size for a lot of small fish larvae, but the adults are too big.

So, to make sure you're only offering the stage 1 nauplii, you could take a 45 micron sieve and pour the Parvocalanus culture into it - the stage 1 nauplii at 40 microns are small enough that they would fall through the sieve's 45 micron holes, but the other stages (including the adults) would be too large to fall through. This lets you collect only the stage 1 nauplii to offer to the larval fish.

Similarly, as the larval fish grow, they can begin eating larger feeders (say, 120 microns, for example), so you can use larger sieves (say 130 microns, for example) to ensure that you keep offering only the feeders which are small enough for the fish to eat (the sieve's size is the maximum size the feeders could be when you offer them to the fish).

Now, while I used copepods for the example above, sieving is useful/needed for things like Artemia nauplii [A.K.A. Baby Brine Shrimp/BBS] as well, since adult brine shrimp are much larger than baby brine shrimp. Again, it's all about controlling what size of feeder you are offering to the larvae.

Typically, when the larvae are ready to settle they're also ready to start being weaned onto "normal" aquarium feeds like frozen foods and pellets, but these also need to be offered in appropriate sizes (Otohime and TDO Chroma Boost pellets, for examples, are available in a wide range of sizes, including sizes that are appropriate for most newly settled fish).


Larval nutritional needs and changes (Bottlenecks):

As mentioned, larval fish have special food needs. Some species need rotifers, others copepods, others Artemia, etc.

For some species, though, those needs change at different points of their larval development. This means that a feeder (such as rotifers) that meets their nutritional needs at one point in their development (such as immediately after hatching) may not meet their nutritional needs at another (such as 15 days after hatching). So, you may need to switch what is being fed (such as switching from rotifers to Artemia nauplii) to the fish at or slightly before that point in order to meet their new/changing nutritional needs.

We refer to these points as "bottlenecks," as the number of larvae that survive beyond these points without a change of feeders is typically very low or zero.

We typically find out about these bottlenecks by - unfortunately - watching them happen. This can be incredibly disheartening, but the good news is that once we have identified a bottleneck (days 2 and 3 post hatch are common bottleneck days, and there's often another bottleneck after about 2-3 weeks), we know to adjust something (typically the feeding) to account for it with the next batch and try to get larvae surviving through it.

Remember, every attempt gets us one step closer to successfully rearing the species - don't give up!
______________________________________________________________________________________
Settlement:

Some species need sand, rock, dark areas, specific colors, specific chemical cues, or other oddly specific things to settle on/in (from what I've seen, inverts are usually a lot more picky with this), so it may help to have a ledge or cave (PVC should be fine for this, if it's even needed, which I honestly kind of doubt) and a little sand in the larval rearing tank just in case the fish need it.
______________________________________________________________________________________
Final notes:

Since marine aquaculture is still a developing field, any information you can gather is helpful for both you and others.

With that in mind:

-Watch for developmental bottlenecks and issues with your rearing methods - some species may require fine-tuning things like the lighting, flow, broodstock (parental) diet, etc. Fine-tune your larval rearing process, and if you can't get past a certain bottleneck, you may need to start looking at things other than the larval foods.

-Observe and note information about the larvae (things like how big the eggs are, how big the larvae are, when the larvae settle, when coloration comes in, etc.) and the larval behaviors (stuff like if they are attracted to light, how they react to light, if they are attracted to certain colors, what feeders they eat and what what sizes of feeders they eat at what days post hatch, what kind of substrate they prefer to settle on, are they cannibalistic, etc.).

Any information you get can bring us closer to success.


Finally, this last link gives a bunch of info on rearing difficult species and some ideas about trying to troubleshoot problems with the rearing:

Has anyone successfully raised Sunshine Chromis from fry?

Hey all, So I have a breeding pair of sunshine chromis in my reef tank. They have laid 3 batches of eggs that I’ve seen so far, and by the third day, all the eggs are gone (I’m guessing the snails knock them off or my purple tang eats them). I managed to collect and hatch a handful from the...

www.reef2reef.com

If you have any questions, please ask - I'll help when I can.

I hope this helps - good luck, and keep us updated!

 

[Jac647]

Yeah, I'd say Skunk Cleaner larvae - for comparison:

https://upload.wikimedia.org/wikipedia/commons/c/ce/Lysmata_amboinensis_zoea_1.jpg

The chances of even one of them surviving are astronomically low - it happens sometimes, but it's not at all common.

If you want to try and rear them in a separate tank:

(The below is general aquaculture info geared toward fish, but most of it's adaptable for inverts like shrimp too.)

Awesome info, ty for the wisdom!