Reef Ramblings

 

When your fish start to spawn often their first efforts, especially with young fish, may not be very productive, as with most things a certain amount of practise is needed before they’ll be able to successfully produce a batch of fertile eggs. The female has to learn how lay her eggs in a tight pattern to help make it easier for the male to swim across them and fertilise them, while the male needs to learn how to make sure his sperm is most efficiently delivered to the eggs. Use this learning period to observe your fish, make notes and record how often they spawn, where they spawn, and if there is any stimulus that initiates spawning. This will enable you to predict when they’re going to spawn – useful information that helps you to plan food raising schedules for the anticipated larvae and also to ensure the prospective parents get optimum feeding when they need it.

Once your fish have got the hang of what to do you may find it worthwhile to just observe the first one or two batches, you can then learn the incubation period of the eggs.

The Larval Rearing Tank.

To raise larvae you need to set up a dedicated larval tank. All the commonly raised species initially require a pelagic environment. This is the reason that it’s virtually impossible to raise larvae in a display tank; the larvae need to remain suspended in the water column, swimming in food, safe from predation, and safe from being sucked into pumps, filters, etc. Requirements for different species may vary slightly but what I’m going to describe is a useful general-purpose setup, suitable for clowns and shrimps.

A good starting point is: a 24” x 12” x 12” aquarium, heater to suit, air-pump, length of flexible air-hose, short length of rigid air-line, thermometer, ammonia alert badge, and some material to shade the tank from light.

Try and limit the amount of hardware in the larval tank as any small gaps around sucker clips and the like, represents potential death traps for larvae. Many larvae are incapable of manoeuvring themselves out of tight spots and can become trapped. This may not be a big problem, considering the numbers of larvae you’ll have, any losses will be insignificant, but it does represent a source of pollution in an unfiltered system that needs to be dealt with – always siphon out dead larvae to minimise pollution. If the tank is in a position where the temperature remains stable and no additional heating is needed it’s an advantage not to have to include a heater.

When you’re happy that you have enough information about the spawning pattern of your fish and feel you’re ready to try raising a batch of fry it’s time to set up your larval raising tank Try and time your set up to coincide with a spawning so the tank doesn’t lie empty too long.

Set the tank up on white polystyrene, this will enable you to see waste material on the bottom of the tank making it easier for you to siphon out detritus when cleaning the tank. Cover the back and sides of the tank with black material, I like self-adhesive Fablon for this, and prepare a removable black cover for the front glass, here I tape bin liner material to the front of the glass in such a way that I can peel it back to observe the tank but can tack it back into position afterwards. The reason for blacking the tank out is to make it easier for the larvae to see their prey and to prevent them from being distracted by light from outside the tank, which could lead to them crowding together in one spot rather than spreading evenly throughout the tank. When the larvae’s eyes have developed a bit more, five to seven days depending on species, you can discard the front cover. Some species may need overhead light limited to an extent, if your larvae are trying to swim away from the light either reduce or shade the light until they’re happy swimming in the water column.

I’d suggest a regular photoperiod of between twelve to sixteen hours, in times of low rotifer production you can use a longer night to enable the rotifers to catch up. Standard T8 lighting is fine for larval raising tanks.

Fill the tank about half full with water from the parental system, fix the rigid airline into a convenient corner of the tank and start off the air pump. You’ll need to regulate the airflow in such a way that you get good circulation throughout the tank with out excessively vigorous bubbling, which could batter delicate larvae. If using a heater turn it on, ensuring it’s covered by the water, and adjust over a period of 24 hours until you’re confident of a stable, suitable temperature, say 27˚c.

Raising the Larvae.

The evening before hatching is due transfer the egg site to the larval tank. Position the substrate holding the eggs adjacent to the rigid airline so that bubbles are gently buffeting the eggs, simulating the fanning of the parent fish. You want to make sure the eggs are being kept constantly in motion, more is better than less here. At this stage I usually add just enough live phytoplankton to colour the water.

Next morning, if you’ve done your sums right, you should have a tank full of tiny larvae. This is where the work starts! Add rotifers to the tank, aiming for the sort of density that means the larvae needn’t swim more than their own length before encountering a tasty rotifer. I’d also increase the phytoplankton density at this time, it’ll do double duty for use both as food for the rotifers and, by utilising some of the waste products from the larvae, help to maintain water quality.

Over the next five days or so keep up the rotifer density and keep a green tinge to the water with additions of phyto. These first few days are where it often all goes wrong. Losses experienced at this time are usually going to be down to lack of food – if you can’t maintain rotifer density the larvae will starve.

Some where between day five and day ten, depending on species, you can move on to newly hatched artemia nauplii. Not all larvae grow at the same rate so do continue with rotifers at the same time. The introduction of artemia does present a risk; the larvae, after days of gorging on rotifers, will try the same with artemia and this can lead to death through choking or overeating, try and limit the feeding of nauplii to something in the region of twenty-five per larva per day, spread over the course of the day.

Many breeders try to keep the nauplii feeding stage as short as possible to limit losses, to do this you need to introduce alternative foods early on. Most breeders favour dry foods but I prefer to utilise as natural a food as possible, so for me this means live or frozen foods of the highest nutritional value, with particular emphasis on high levels of the highly unsaturated fatty acids (HUFAs) EPA and DHA. I add a small amount of frozen Cyclop-Eeze, graded to size by “mashing” through a 180 micron sieve, right from day one, increasing the amount as I see it starting to be taken, with the aim of getting the fry onto whole frozen Cyclop-Eeze as soon as I can. Other breeders start off with powdered flake food, gradually increasing the size of particles used to a size suitable for your young fish. Your youngsters will need to learn that this strange, unmoving stuff on the surface of the water is edible, so a food with a high attractant quality, such as Cyclop-Eeze, will bring quicker results – try feeding new foods first thing in the morning when everyone’s at their hungriest, they will accept dry food gradually, probably following by example one of their more adventurous brethren. Of course the down side of moving on to frozen and dry foods is pollution, try and clean out all uneaten food and minimise the amount you introduce until your sure it’s being eaten.

Water Quality.

This brings us to the topic of water quality. You’ll have noticed earlier that I suggested starting off with the larval raising tank half full; there are couple of reasons for this. Firstly by minimising the volume of water you can more easily maximise rotifer density making it easier for newly hatched larvae to hunt. Secondly you can avoid doing water changes that involve siphoning while the larvae are really tiny, instead add water from the parental tank to dilute pollution, topping up the parents tank with new salt water. Use your ammonia alert badge to warn you of any problems with water quality. Don’t be unduly worried about low pH readings on larval raising tanks. At a pH of 7.5, not unheard of in a larval tank, you have the advantage that any ammonia present is non-toxic; in an unfiltered tank ammonia is almost inevitable but as pH increases so does ammonia’s toxicity.

When you’re running the tank at full water volume start doing small daily changes, again with water from the parents tank. Once you’ve weaned your youngsters onto a dry food diet add an air powered sponge filter to their tank. It’s a good idea to run this filter in the parent’s tank first, and then instead of actually cycling the filter in the fry tank you’re simply putting in a mature filter.

From here on I’d like to say it’s just a matter of feeding hungry little mouths and keeping the water quality high but I’m afraid you’ll find there’s a bit more to it than that. If you do decide to have a go at raising larvae I’d like to urge you to go out and get yourself a copy of Joyce Wilkerson’s excellent book Clownfishes or Matt Wittenrich’s Breeders Guide to Marine Aquarium Fishes. Both cover far more than I can in a couple of articles, essentially what I’ve written here is to give you a taste of what marine breeding’s all about. It can be difficult, you may not succeed first time but I can assure you that when you do it’s a very rewarding experience.

Invertebrates.

Lysmata wurdemanni or peppermint shrimp is by far the easiest invertebrate you can have a go at raising. The set up described above for fishes will work for raising these but pay extra attention to keeping the larval tank clean and preventing any build up of hair algae on the sides or base. If the larvae get caught up in hair algae they’ll die.

You don’t need to use rotifers with shrimp larvae, you can just rely on freshly hatched Artemia, gradually upping the size as the larvae moult and grow.

If you don’t feed enough the larvae will resort to cannibalism – so beware!

A Question of Gravity.

One thing I’d like to draw your attention to is the question of what specific gravity to use when embarking on a breeding project. It’s accepted practise for reef aquariums to keep salinity at natural sea water levels –35 parts per thousand (ppt) or roughly a specific gravity (S.G.) of 1.026 at 26˚c. When raising larvae and their associated live foods it becomes advantageous to work at lower salinities, the reasoning behind this is that rotifers grow and reproduce at a faster rate when kept at lower salinities than usually used to maintain marine animals. Rotifers are intolerant of a change in specific gravity greater than seven points i.e. a difference of .007 and grow best in a range of specific gravity between 1.007 and 1.014. From this we can determine that to raise marine fishes most effectively we can use a rotifer culture S.G. of 1.014 along with a larval tank S.G. of 1.021, phyto is not so fussy so I grow mine at a S.G. of 1.015.

Because of all this some breeders also maintain their brood stock at a lower S.G. As an aquarist who’s more interested in learning about and researching the captive marine environment, rather than breeding regular quantities of fish, I maintain all my tanks at 35 ppt but then gradually reduce the salinity of any larval tank prior to hatching by the slow addition of R.O. water. The choice is up to you.

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If you have any queries relating to this, or any other article published at Reef Ramblings, please don’t hesitate to contact me.

Tim Hayes

Midland Reefs

©2007 – 2012