Yes, sir, live rock and live sand are best avoided for nursery tanks to help minimize problems with hydroids, and it is customary to leave the nurseries bare bottomed for sanitary purposes to facilitate cleaning and maintenance.
Most nursery setups are bare bottom tanks that rely on twice daily (minimum) water changes to maintain optimum water quality. Siphoning the bottom at least twice a day is necessary due to the amazingly rapid production of fecal pellets the voracious fry generate, and a bare glass bottom facilitates the vacuuming process. The siphoning removes a small amount of water, which is replaced with freshly prepared saltwater, as discussed below. Simple air-operated sponge filters may be included to provide biological filtration, but that does not eliminate the need to make daily water changes while siphoning up the fecal pellets from the bottom.
Basic Nursery Tank
The simplest nursery tank setup is a bare bottom 5 to 10-gallon glass tank equipped with suitable hitching posts, an air-operated sponge or foam filter, and nothing else (Giwojna, Jan. 1997). Add a cartridge of activated carbon to the airlift tube of the sponge filter(s) to provide a little chemical filtration.
Keep the sponge filters in such nurseries elevated or prop them up off of the bottom. Otherwise they can become death traps for unwary benthic fry, which can become wedged beneath them and trapped. Adjust the airflow through the sponge so it produces a stream of small, steady bubbles. You want to create a slow, gentle flow through the foam filter without generating overly fine or excessively large bubbles (Giwojna, Jan. 1997). Seahorse fry may accidentally ingest fine bubbles, mistaking them for food, while large bubbles can buffet the newborns with harmful results (Giwojna, Jan. 1997). Too much airflow through the sponge filters will leave them prone to "eating" the fry’s food (newly hatched Artemia, copepods, rotifers, etc.).
At the same time, however, you want the air stream to break up surface tension and provide adequate surface agitation. This is important not only for efficient oxygenation and gas exchange at the air/water interface, but also to allow the fry easy access to the surface. A newborn’s first instinct is to head to the surface to fill its swim bladder. (Physosymotous fishes have a connection between their gas bladder and the gut in the form of an open tube called the pneumatic duct, and are thus able to fill the swim bladder by gulping air at the surface. Like many teleost fishes, seahorses lose this connection very early in life, so that their swim bladders are completed closed as adults.) In many species, gulping air is the way in which gas is first introduced into the larvae’s bladder, and if denied an opportunity to do so, their development is hampered due to uninflated swim bladders (Silveira, 2000).
This is the case with seahorse fry. If denied access to the surface to inflate their swim bladders, the fry behave normally while they are small and their weight is still negligible. But over the weeks, as they grow and put on weight, their underdeveloped swim bladders and inability to achieve neutral buoyancy increasingly handicap them. Once they gain a little weight, they sink like rocks. Unable to swim, they are reduced to slithering along the bottom on their bellies and are commonly referred to as sliders. This deficiency does not become apparent until the fry are several weeks old. Needless to say, this hinders their swimming ability and severely limits their feeding opportunities, delaying their growth and development, and rendering entire broods useless. In several cases, the problem was traced back to an oily film on the surface of the nursery tank, which prevented the newborns from filling their swim bladders with air (Silveira, 2000). A protein skimmer will prevent this by removing filmy surface layers and surfactants in general.
The same sort of sponge filters that work well for dwarf seahorse tanks are also ideal for nursery tanks. Be sure to avoid sponge filters with weighted bottoms or other metal components since they will rust when exposed to saltwater. Sooner or later this will cause problems in a marine aquarium (sooner in the small nursery tanks). Select a sponge filter that has no metal parts and is safe for use in saltwater. The proper units will have suction cups to anchor them in place rather than a weighted bottom.
The sponge filters I find that work well are the Oxygen Plus Bio-Filters (models 2, 3, 4, or 5) or the Tetra Brilliant foam filters. They have no metal components, making them completely safe for use in saltwater, and just one of these foam filters will do the job on a tank of 5 gallons or less. They do not have a weighted bottom but are equipped with suction cups instead.
Click here: Foam Aquarium Filters: Oxygen Plus Bio-Filter 2
Avoid the Oxygen Plus Bio-filter 6, 11, and the Multi sponge, which all have a weighted bottom (metal), that rusts when exposed to saltwater. If you want more filtration, you’re better off going with two of the smaller suction cup sponge filters rather than any of the models with weighted bottoms. For instance, for a 10-gallon tank, I’d suggest using two well-established foam filters, one at either end of the tank for the biofiltration, just as you are planning, Alex.
All you need to operate sponge or foam filters is an inexpensive, diaphragm-operated air pump (whatever is available at a reasonable price from your LFS will do just fine), a length of airline tubing to connect the air pump to the foam filter(s), and a set of air valves (gang valves) to regulate the air flow to the filters. That’s all — nothing to it! The inexpensive Apollo 5 air pumps work great for sponge filters, but whatever air pump you have on hand should certainly do the job.
Cleaning the foam filters is a snap. Simply immerse them in a bucket of saltwater and gently squeeze out the sponge until it’s clean and releases no more sediment or debris. (I use the saltwater I siphoned out of my aquarium when performing a water change for this, and clean my sponge filters whenever I change water.) Run a bottlebrush through the inside of the tube, wipe off the outside of the tube, and you’re done. The filter is ready to go back in the aquarium with no impairment at all of the biofiltration. Takes only a couple minutes.
Setting Up & Maintaining the Nursery.
The nursery tank(s) should be filled with water taken from the main tank that houses their parents, so the delicate newborns can be transferred directly to the nursery without adjusting to any stressful changes in pH, temperature or salinity (Giwojna, Jan. 1997). Cured ”seahorse trees” make good hitching posts, as do artificial aquarium decorations such as small seafans and soft plastic plants with fine, branching leaves (Giwojna, Jan. 1997). Strips, sections, and cylinders of plastic window screen or the plastic mesh sold in craft stores for needlepoint projects also work well. Short lengths of polypropylene rope (the kind sold at hardware stores and marine outlets for boating purposes) are another good option for hitching posts in the nursery. They come in many different colors, can be cut to any desired length, and are buoyant so if one end is anchored and the other end is unraveled, they will wave gently in the current like natural plants. (Avoid nylon rope, however — it bleeds in saltwater and will leech color and who knows what else into your tank!) If necessary, the holdfasts can be secured to the bare glass with silicone aquarium cement or suction cups designed for use in marine aquaria, or secured to a piece of coral rubble to anchor them in place.
If you can obtain the fine-bladed or feathery varieties, live Caulerpa will help maintain good water quality by removing excess nitrates, as well as providing natural hitching posts that help benthic seahorse fry feel right at home (Giwojna, Jan. 1997). These marine plants grow from woody holdfasts and don’t need to be anchored in a sand or gravel substrate, so they’ll do fine in a bare-bottomed nursery (Giwojna, Jan. 1997). However, live Caulerpa is more difficult to keep clean and sanitary, and for this reason, many breeders prefer artificial hitching posts for their nurseries such as those described above (Mai 2004b).
In addition, hydroids and miniature jellyfish (the free-swimming hydromedusae stage of the hydroids) are often present on live marine plants, and they can easily be accidentally introduced to the aquarium along with the Caulerpa. Ordinarily, this is not a problem for the greater seahorses, but hydrozoans can wreak havoc when they become established in a nursery tank. Not only will they compete with the fry for food, their stings can be lethal to the babies or leave them susceptible to secondary infections (Vincent, 1995c), and hydroids are sometimes responsible for mass mortalities in nurseries.
A brief quarantine period for Caulerpa and other marine plants, during which they can be treated with fenbendazole granules for several days, is therefore strongly advised. Fenbendazole is an inexpensive deworming agent used for hoses and other large animals, and treating the quarantine tank with 1/8 teaspoon per 10 gallons is guaranteed to eradicate hydroids before they can gain a foothold in your nursery tank (Liisa Coit, pers. com.).
Good lighting is also essential for the nursery tanks. The fry must be able to see the tiny organisms they live on clearly in order to feed efficiently. Use ”Daylight” fluorescent tubes or the equivalent and leave them on for a minimum of 14 hours a day, since the fry need to eat for at least 12-14 hours everyday (Vincent, 1995c).
Since the nursery tanks have limited filtration, daily water changes are needed in most systems to maintain water quality and keep up with the metabolic wastes and oxygen demands of several dozen baby sea horses and the thousands of brine shrimp needed to feed them (Giwojna, Jan. 1997). When the fry are well fed, defecation is amazingly rapid, with each newborn producing an average of one fecal pellet every 25-30 minutes (Herald and Rakowicz, 1951). The best way to perform the necessary maintenance is to use a length of airline tubing to siphon off the bottom of the nursery tanks a minimum of twice a day (morning and evening are ideal for this; Giwojna, Jan. 1997). Replace the water that was removed while siphoning with freshly mixed saltwater that has been pre-adjusted to the same temperature, pH and salinity as the rearing tank. Change about 10-20% of the water each time you siphon the bottom, so that a total of at least 25-50% of the water in the nursery tanks is exchanged every day (Giwojna, Jan. 1997).
Blacking out the top 2/3 of the aquarium and using side lighting or bottom lighting are techniques that are often used to help keep pelagic seahorse fry away from the surface, but there are many other (and better) nursery tank designs such as kriesels/pseudokreisels and in-tank nurseries that are more efficient at preventing surface huggers and floaters.
That’s the quick rundown on how to set up a basic nursery tank for seahorses, Cajun, and if you contact me off list ([email protected]) I will be happy to provide you with some more detailed information regarding various nursery tank options and feeding regimens for the newborns to help get you started off on the right foot. Those are files that are too large to be posted here in this forum.
Best wishes with all your fishes, sir!