Re:arrow head crabs

#3742
Pete Giwojna
Guest

Dear FERS4REEF:

Congratulations on your upcoming brood of babies!

The bristleworms in your seahorse tank shouldn’t present a problem for the babies because Hippocampus kuda produces pelagic fry that will cluster at the surface of the aquarium, well out of the reach of the bristleworms, and you will be transferring them into a separate nursery tank for rearing as soon as possible.

I wouldn’t recommend using a small arrow crab or any predatory fish to control the bristleworms in your case, since they are very likely to present a risk to the newborn seahorses. Any fish with mouths large enough to swallow the newborns are apt to prey on the seahorse fry. Likewise, decorative shrimp of all kinds — fire shrimp, cleaner shrimp, peppermint shrimp, etc. — will actively prey on seahorse fry and can rapidly decimate a brood. Snails are just fine but crabs of all kinds can pose a risk to the newborns after the fry pass through their pelagic phase and begin to orient to the substrate. Scarlet reef hermit crabs (Paguristes cadenati) and micro-hermit crabs that stay tiny and micro stars (miniature brittle starfish with a leg span no greater than perhaps a dime) are usually okay, but larger hermit crabs and serpent starfish may become opportunistic predators of baby seahorses.

A medium-size arrow crab would probably coexist just fine with the adult H. kuda, but but it would also be an efficient preditor on newborn seahorses, so I would look elsewhere in your case.

Stinging animals such as hydroids (both the colonial stage and the hydromedusae jellyfish) and anemones can also take a heavy toll on the newborns.

Other than that, you just need to make sure that your filters and overflows don’t "eat" any of the newborns. Hippocampus kuda fry go through a pelagic or free-swimming planktonic stage and tend to cluster your the surface for the first several days of life, and these surface huggers are vulnerable to overflows and prone to getting filtered out, so beware of that as well.

In my opinion, it’s best to leave the male in the main tank where he is most comfortable and allow him to deliver his brood there. While you are waiting for your pregnant kuda to complete his gestation, prepare a suitable nursery tank (as discussed below) and then simply relocate the newborns from your seahorse tank to the new nursery when they are born.

When transferring the fry, scoop them up in a small measuring cup or something similar along with a little water. It’s important that the newborns aren’t exposed to the air during the transfers. Or a plastic turkey baster works well for delicately sucking up the fry when transferring them, providing you cut off a bit from the tip of the baster to enlarge the opening at the tip.

Your 10-gallon quarantine tank will suffice as a 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
http://www.drsfostersmith.com/product/prod_Display.cfm?siteid=6&pCatId=3936

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 14-17 hours a day, since the fry need to eat for at least 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.

Ordinarily, bristleworms only become problematic when they are either too numerous or too large. When their numbers increase to the point where they are swarming the feeding station, they could present a danger to your seahorses when they are eating and the bristleworms should be thinned out. Likewise, any bristleworms that have grown to a length of 2-3 inches or more are quite capable of delivering a nasty bite to a seahorse (or an unwary aquarist) and the larger specimens should therefore be weeded out. So whether or not the bristleworms can coexist with your seahorses safely depends on how large and how numerous the worms are, FERS4REEF.

Since trapping the bristleworms isn’t producing satisfactory results, you could always eradicate them altogether using an anthelmintic agent (i.e., dewormer) such as fenbendazole (brand name Panacur), providing there are no sensitive invertebrates (corals, feather dusters, etc.) that could be harmed by the medication. Let me know if you feel it would be appropriate to eliminate the bristleworms from your tank using a deworming agent, and I will be happy to provide you with instructions explaining exactly how to proceed.

Best of luck with your pregnant kuda and his future offspring, FERS4REEF!

Happy Trails!
Pete Giwojna


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