Lining up your food sources and preparing for your reidi fry ahead of time is an excellent idea. If the pouch changes you have noticed don’t indicate that your male is pregnant at the moment, they certainly do indicate that he is preparing his pouch for breeding, and that he will be mating soon. Either way, you’re absolutely correct that it’s best to get your nursery tank and live food cultures ready in advance.
Yes, sir, your adult reidi can survive in hyposalinity at a specific gravity of 1.016 without any difficulty whatsoever. In fact, you can transfer them from the normal salinity in your reef tank to water of reduced salinity at 1.016 without any acclimation needed at all.
However, that’s not the best way to go about it if you are planning on using your five-gallon nursery tank as a paternity ward, Nigel, because your stallion would need to be very carefully and gradually acclimated back to the normal salinity afterwards in order to avoid the danger of dehydration. I would adjust the specific gravity in your 5 gallon nursery tank to the same specific gravity as a reef tank if you are going to briefly confine your male reidi in the nursery tank while he gives birth. That way, your stallion can be returned to your reef tank immediately after he gives birth without any need for acclimation, which should minimize the stressful effects of transferring him around like that.
However, your adult H. reidi are not going to be able to survive in a five-gallon tank without any biofiltration for any length of time regardless of what the salinity of the water is. They cannot make in an aquarium that shallow and there are going to be ammonia spikes that you will need to control with water changes as often as necessary (at least once a day). So if you’re going to try to use your five-gallon nursery tank as a paternity ward, Nigel, wait until birth is imminent so that your stallion isn’t cooped up in that tiny aquarium for any more than a day or so, and make sure the tank has plenty of shelter and hitching posts so he won’t fill vulnerable and exposed. Keep the nursery tank at the salinity of your reef tank so your stallion can go back into your reef tank immediately after he delivers his brood.
Then, after the male has been returned to your reef tank, you can reduce the salinity in the nursery tank to 1.016 to reduce the buoyancy of the newborns and help keep them away from the surface.
Yes, newborn reidi can eat copepods that are at the right stage of development, and copepods are the most nutritious food that seahorse fry can eat. Marine copepods are the ideal food for rearing seahorses fry. They are a natural prey item that constitutes a large portion of the diet of fish larvae in the ocean, and many marine fishes have evolved efficient feeding strategies for preying on them as their primary foods. This includes seahorses, whose tubular snouts are adapted specifically for feeding on tiny crustaceans such as ‘pods, and which have developed a sedentary lifestyle as ambush predators that allows them to capture them with maximum efficiency and a minimum expenditure of energy. The tiny size of the copepod nauplii allows even the smallest seahorse fry to eat them, and they are a feed-and-forget food that will survive in the nursery tank until eaten. The distinctive swimming style of copepod nauplii triggers a strong feeding response from seahorse fry, and ‘pods have naturally high levels of essentially fatty acids. They are superior to rotifers in all these respects (seahorse fry often reject rotifers because they don’t move in the "right" way and simply don’t trigger their feeding instincts) and I recommend that aquarists who are raising pelagic fry concentrate on culturing copepods.
Seahorse fry alter their diet as they grow (Vincent, 1990). This may be due to the fact that they change microhabits as they develop (e.g., when pelagic fry complete their planktonic stage and begin to feed at the bottom as they begin orienting to the substrate). Or it may simply be due to the fact that they become better hunters and perfect their feeding skills as they grow, thus enabling them to tackle larger, more active prey (Vincent, 1990). Whatever the cause, one good way to keep up with the fry’s changing dietary requirements is by providing them with cultured copepods at progressively later stages of development.
Step 1: Providing Marine Microalgae (Phytoplankton).
Marine microalgae or phytoplankton is available from many sources. It can be cultured at home, and if you have a green thumb and are experienced with such greenwater cultures, that may be your best option. However, home culturing may not be for everyone. Greenwater cultures can be tricky to maintain. They are easily contaminated and are prone to "crashing" suddenly and unpredictably, which can have dire consequences if you are relying on the phytoplankton to provide food for your seahorse fry.
Alas, I am one of those unfortunates who cannot seem to maintain a decent greenwater culture for any length of time no matter what I try. Consequently, I now much prefer to obtain live marine phytoplankton from other sources rather than attempting to culture my own. Commercially available phytoplankton tends to be more concentrated than homegrown cultures as a rule, and I find purchasing it to be far more convenient, efficient, and productive. Given my repeated failures and the time I spent for naught on my own greenwater cultures, I’m certain that buying live phytoplankton is more economical for me in the long run as well. If you are inexperienced with greenwater culture or simply lack the time to culture your own, I recommend buying your live phytoplankton instead (see the Resources page for suppliers). Whichever source you decide to use, home grown or store bought, make sure you use it strictly according to instructions to prevent contamination and spoilage of the phytoplankton.
The type of phytoplankton or microalgae you use is not that crucial. Chlorella is one of the most popular microalgae used in mariculture (Wilkerson, 1995), but Dunaliella also works extremely well and is recommended by Dr. Amanda Vincent (Vincent, 1995c), an authority on the breeding habits of seahorses. Serious breeders often use a mixture of different types of phytoplankton to feed copepods or rotifers, rather than a microalgae monoculture, with the goal of enhancing the nutritional profile of the ‘pods or rotis as much as possible (David Warland, pers. com.).
There is a great deal of merit to that approach, but in the past, maintaining separate cultures of different species of microalgae was beyond the capabilities of most home hobbyists, myself included. I prefer to keep things simple and I have always used Nannochlroposis as the phytoplankton I feed to copepods, both because it produces good results and because it is commercially available from a number of sources. To simplify things all the further, I purchase my Nannochlroposis in quantity as needed, rather than struggling with phytoplankton cultures.
The product I like best at the moment for this now includes a concentrated mixture of live marine phytoplankton (two species of Nannochlroposis, N. oculata and N. salina, as well as a Chlorella sp.) in every bottle (DT’s Live Marine Phytoplankton, 2003). That makes it a simple matter to provide my ‘pods with a diversified diet to maximize their nutritional value as fry food — I just unscrew the cap on the bottle and pour the requisite amount of this phytoplankton mixture into my culture tank whenever it’s losing its greenish tinge, and I’m in business (DT’s Live Marine Phytoplankton, 2003)! No muss, no fuss. Quick, easy and effective — just the way I like it!
Step 2: Culturing Zooplankton (copepods and/or rotifers).
We will be using standard 10-gallon glass aquaria as our batch culture tanks. It’s a good idea to run at least 2 such tanks simultaneously; that way, if one of the cultures falters, the other tank can pick up the slack and you won’t miss a beat. Depending on how many seahorse fry you are rearing, you many need to operate several such tanks to assure you will be producing sufficient food for them all.
Fill each of these culture tanks slightly less than half full with synthetic saltwater, adjust the salinity of the culture tank to match the salinity of your nursery tanks, and maintain the pH at 7.9 or below (Rhodes, 2003). This will assure that the copepods (or rotifers) we are culturing do not experience any salinity shock when we feed them to our seahorse fry. No heater is necessary — the cultures will do just fine at room temperature (24C-28C is optimum). Provide very low aeration (Rhodes, 2003). Airstones are unnecessary — a naked bubbler stem is sufficient. Adjust the airflow so it produces a slow, steady stream of coarse air bubbles (slow enough so that you can count the individual bubbles). Ambient room lighting is adequate or you may provide low wattage fluorescent lighting if you prefer.
Add enough greenwater (either commercially produced phytoplankton you’ve purchased or your own homegrown microalgae) to tinge the culture tanks green, and you’re ready to start culturing copepods. All that remains at this point is to "seed" the culture tanks with copepods. Add a starter culture of marine copepods to each tank, acclimating the ‘pods if necessary exactly as you would acclimate a new aquarium fish. They will do the rest.
To nurture the copepods, simply maintain a nice green tint to the culture water by adding more phytoplankton whenever the water in the tanks begins to clear in color. (Be conservative with these phyto-feedings. One dose of phytoplankton every 7-10 days is generally adequate, depending on production and your copepod harvest rates; Rhodes, 2003.) The ‘pod population in the culture tanks will double every 2-3 days, depending on the temperature and how well they are fed (Rhodes, 2003), and as soon as the population builds up sufficiently, we can begin to harvest copepods to feed to our seahorse fry. When you begin to notice numbers of copepods gathering on the tank glass, that’s a good indication that their population density can support daily harvesting.
The best way to harvest copepod nauplii is to strain the desired amount from the culture tank using a 35-micron sieve and then rinse or backwash the strainer in the nursery tank (Rhodes, 2003). Alternate which culture tank you harvest the copepods from for each feeding in order to avoid depleting the ‘pod population too much in any given tank.
Periodically, it will be necessary to restart the copepod culture tanks to filter out the detritus that accumulates on the bottom. This is typically done every month or two (Rhodes, 2003) and is a surprisingly simple process. Just siphon out the water from the culture tank, straining the water in the process in order to retain the copepods. A 125 -micron sieve works well for a strainer. That size mesh will retain all the reproductive adults you need to restart your culture (Rhodes, 2003). It’s a good idea to use a small diameter siphon at first, being careful to suck up as little of the detritus as possible since it will clog up your strainer and your goal at this point is to recover as many copepods as you can. Once you’ve strained out most of the ‘pods, backwash them into container of clean saltwater and set them aside to seed the culture tank after you’ve finished cleaning it. Having saved as many pods as possible, switch to a larger siphon and drain the culture tank completely, removing all of the accumulated detritus. Fill the tank half way with freshly mixed saltwater you’ve prepared in advance and adjust the aeration. Then return the copepods you strained out previously and add enough concentrated phytoplankton to tinge the water green, and your culture is ready to begin producing again. If you restart your culture tanks on alternate months, one or more of them will be in full production at all times, and you can keep a thriving copepod population going indefinitely in this manner.
If you so desire, rotifers can be cultured in exactly the same manner. The only difference is that the 10-gallon culture tanks should each be seeded with a quart of live rotifers initially (Giwojna, Jan. 1997). When necessary, add enough concentrated phytoplankton or greenwater to keep the rotifer culture tanks slightly green. As long as the rotifers are being fed algae, about 25% of the rotifer cultures can be harvested each day to feed to your seahorse fry (Wilkerson, 1995). Try to keep more than one rotifer culture going at all times in case of crashes, and be sure to keep the bottom of the culture tanks scrupulously clean (Giwojna, Jan. 1997).
In fact, you can even maintain a dual culture of copepods and rotifers in the same tank if you wish. But you must avoid cross-contamination of your culture tanks with brine shrimp at all costs! Newly hatched brine shrimp (Artemia nauplii) are considerably larger than either copepods or rotifers, and the Artemia will happily fed on them as well as the phytoplankton. So if any brine shrimp ever find their way into your culture tanks, you will very shortly thereafter be culturing Artemia instead of ‘pods or rotis, leaving you with nothing but live food that’s too large for pelagic fry to eat.
Harpacticoid copepods such as Nitokra lacustris go through 6 naupliar stages as they grow, followed by 6 copepodite stages, before they become reproductive adults. They range in size from 45 microns (smaller than rotifers) up to 270 microns as full-sized adults. The many different stages of development copepods undergo is actually a blessing for the aquarist since it makes it possible to provide progressively larger ‘pods to the seahorse fry as they grow simply by using sieves with different sized mesh to harvest them. For instance, a 35-micron sieve will gather up even the smallest copepod nauplii for newborn fry, while a 125-micron will collect only adult-sized pods for older fry and juveniles, leaving the smaller ‘pods behind to develop further. An 80-micron sieve will take intermediate-size ‘pods along with the adults.
Whether you’re culturing rotifers or copepod nauplii, pelagic seahorse fry should be fed continuously starting 6-12 hours after birth (Giwojna, Jan. 1997). Dr. Amanda Vincent recommends feeding 2 plankton nets of rotifers (or ‘pods) 5-7 times daily or whenever no plankton is visible in the nursery tanks (Vincent, 1995c). In addition, she keeps a drip of diluted plankton (i.e., rotifers or copepods) going at the rate of 10 liters/day at all times (Giwojna, Jan. 1997). (A bucket of copepod-laden or rotifer-rich saltwater set on top of the nursery tank will suffice for this–just use a length of airline tubing as a siphon and adjust the drip rate with a valve; Vincent, 1995c.)
Ocean riders doesn’t sell rotifers, but starter cultures are available from a number of places online. You should be able to get greenwater (microalgae) and/or copepod starter cultures from the same place you get your rotifers.
Best of luck rearing your reidi babies when they arrive, Nigel!