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Captive Marine Fish Rearing

Maria-Laura C. Harris


Welcome everyone, and thank you for the opportunity to speak at tonight's #reefs. Tonight's topic is captive marine fish rearing, a huge topic which will make it difficult for me to cover all areas in tonight.

Any questions concerning the life-cycle and spawning of specific species should be researched in the literature, as it is there where one can learn about the natural conditions that need to be present to induce species to spawn, and in some cases, actually show how it was copied in an artificial environment.

Also I am concentrating on natural induced spawning, not stripping, or hormone injection induced....those alone are for another talk and risky for the I have participated in such methods myself.

I welcome questions on this topic, but will not be able to answer most of them in the matter some good literature will. I have dabbled with neon gobies, high hats, jawfish, cardinals, porkfish and royal grammas.

Neon gobies and high hats I have reared successfully into adulthood, time was too short to successfully refine the techniques, in my situation, to successfully rear the others.

That brings my to the most important point: You must be patient and allow yourself a large time frame: It took me over a year to successfully rear high hats from full grown, healthy adult broodstock, and that was after using a variety of techniques to find what worked in my case.

I am here to give an overview on the need for research into propagation, a quick overview of spawning techniques/reproductive biology, opportunistic vs. targeted species rearing, life-support system design, foods, and methods.

After the intro I invite questions regarding the above topics from everyone.

Let us begin by defining the need for further research into mariculture in general:

Worldwide there has been an increasing demand for ornamental fishes by hobbyists and public institutions.

While most of the freshwater species can be supplied through commercial tropical fish farms, most of the marine species available are caught from the wild, and this practice may have led to over-fishing and stock depletion on some areas, as is expressed in recent literature.

This problem also encompasses the frail state of marine invertebrates in the wild, and as we all know many a reefkeeper has at least considered dabbling in the art of propagation, and new results/techniques are constantly being published.

The cost of developing techniques for mass captive propagation of marine fishes is high, and most complicated, although necessary in order to ensure continued availability of the required specimens.

By complicated I mean the addition of a variety of homemade "tools", larval foods, and lots of extra tanks!

Institutions, organizations, commercial businesses such as C-Quest, and some very dedicated hobbyists are working together almost as a network in developing proven techniques for rearing a large number of species.

This can prove to be an effective approach, as large numbers of species can be worked on and the costs of R and D be kept down a tad.

Next topic: Opportunistic vs. Targeted species spawning and rearing.

Are you dreaming of successfully rearing one particular species? Or is there already some "love" going on in your display tank?

Before anyone gets excited over the prospect of rearing flame angels for example, I will provide a list of popular species that, to my knowledge, have not been raised successfully in a closed system environment on artificial foods.

If anybody is curious as to why, please go ahead and ask questions later...the answers are complicated, and literature tying it all together is preliminary to this point.

These species include the tangs, angels (natural system only), butterflies, triggers (natural system only), groupers (natural systems). I know I am missing some...but these are the more popular examples.

Note by natural system I mean natural seawater and the naturally occurring, geographically correct plankton towed from the ocean.

In turn, some of the popular species reared thus far under artificial conditions, and are within the hobbyists grasp are : clowns, damsels, gobies, cardinals, jawfish, basslets/dottybacks, sciaenids (jacknife, high hats), and I am sure I am missing a few here as well...and I cannot forget to tack on some inverts such as clams and shrimps.

Now as the name implies, opportunistic spawning is already occurring in your tank without you, the hobbyist, having to artificially mimic the conditions that need to be present in order for spawning to be induced.

Yes, all the hormones are acting as one in the proper order, and the final kicker, the gnrh hormone, is activated naturally.

The gnrh, or gonadotropin-releasing hormone, I call the kicker because, even though the fish may be perfectly conditioned and full of eggs as far as the female is concerned, and all other factors are in place, the reproductive cycle is arrested at this last stage until environmental conditions are correct and this gnrh released induces the actual spawning.

In targeted spawning, you must take your healthy, well-fed specimens and gradually condition them to final spawn inducement through gradual manipulation of photoperiod, temperature, salinity (this is where literature is so important!), all the time monitoring your water quality parameters carefully (crucial to both fish and eggs).

Whichever way you follow, note down the time interval between successive spawnings on your own specimens, so you become familiar with the timing...which will help you on to the next step: capturing the larvae/eggs (whichever is applicable). Use this time to design your egg (in scatterers such as sciaenids) and larval catcher (in demersal spawners and mouth brooders.

Note: In demersal spawners it is possible to encourage spawning on a removable substrate i.e. the clam in neon gobies, and remove it from the spawning tank to the rearing tank when the eggs are ready to hatch (again, take notes on time to hatch over a few spawnings...learn the changes in your eggs!)

If removal is possible, that solves your problem of trapping the larvae. If not, you can opt for placing a micron bag in your overflow (submerged in a makeshift sump) and placing a light there in the case of larvae, or forgo the light if you are trapping buoyant eggs.

Make sure the current is soft, eggs are easily damaged.

Well, the old method of standing over the tank with a flashlight in hand and skimming the water with a beaker when you see the larvae works well, but has its disadvantages. The first is timing, you could miss the hatch.

The second is merely going nuts with this chore (been there, done that!).

There are several articles describing a variety of home grown larval catchers......view the diagrams and see if you too can build one to suit your needs.

Before I get too carried away, lets move on, any questions will be answered later.

Now on to the rearing tank:

I prefer conical ones with a sloped bottom (easier to siphon off the debris), and painted black (you still need to control the photoperiod at this point, not to mention the "gunk" is more visible), with a standpipe in the middle covered by a 53 micron screen.

An airstone at the side of the pipe aerating gently will help to keep the food and babies off the screen, and allow for good filtration. A large reservoir with plenty of metal removing resins (hopefully you had access to RO water!) and overkill on filtration is best.

Please note: metals are deadly to these babies! Please do all you can to obtain iron-free etc. water, and use a premium salt mix.

If all you have is a bare rectangular tank, with no fancy equipment, this can work too! I am just presenting my ideal scenario.

With a little trial and error, plus imagination, anything can work. The important thing is to provide aeration, no strong currents/filtration, and impeccable water quality.

Important: A debris needs to be siphoned out at least twice a day and pristine water conditions should be present.



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