Re:baby seahorses!!!

Pete Giwojna

Dear hobbyist:

Congratulations on getting so many of the seahorse fry past the four-week mark! You are doing very well for your first attempt at rearing. I’ll do my best to answer your additional questions one-by-one below:

1. i still have them in an in tank nursery, although i have upgraded them to a 1-gallon container. i’m considering putting in a tank divider soon to give them more room in the tank. can you give me an idea how much room they will need as they grow, and how many i will ultimately be able to keep in a 55 gallon tank?

It is customary to transfer the seahorse fry to a series of larger nurseries and grow out tanks as they mature, so the appropriate stocking density for the youngsters depends upon their age and size. For example, the recommended stocking density for pelagic seahorse fry such as Mustangs or Sunbursts is no more than 6 fry per liter, or a maximum stocking density of about 25 fry per gallon. If your nursery tank holds 10 gallons, for example, it can hold about 200 newborns when stocked to capacity, and for best results I would keep it understocked.

Typically by the end of their third week, the fry have grown enough that there stocking density needs to be reduced to maintain adequate water quality and promote further growth. Thus, at this age, the appropriate stocking density for the juveniles is about 7-10 fry per gallon of water.

Ordinarily all of the fry have successfully made the transition to minced Mysis by the age of 7-8 weeks. At this stage, the juveniles are then transferred to larger grow-out tanks for further rearing at a stocking density of 3-4 per gallon.

By the age of about 12-weeks old, the first indications of pouch development may appear. This takes the form of a darkened patch of skin where the pouch will eventually develop (i.e., a nascent pouch is not present at this stage of development, just a patch of pigment). You’ll want to achieve a stocking density of about 2-3 of the youngsters per gallon for three-month-old seahorse fry at this stage of development.

The juvenile seahorses should be segregated by sex as soon as you can accurately determine their gender if you want to practice selective breeding. That allows you to pair off seahorses with the particular traits you want to encourage in the next generation, and the recommended stocking density for sexually mature H. erectus is one pair per 10 gallons. So you’re 55-gallon aquarium could safely accommodate five pairs or about 10 individual adult seahorses.

2. at what point should i be expecting all these little guys to die?? from everything i’ve heard, i didn’t expect them to survive the first week, much less the first month. or is it typical for them to survive a couple of months, but still die before becoming fully grown? that would really stink, as my kids are starting to NAME them…

In general, mortality rates among the newborns and juveniles decrease steadily as they grow, so the older the juveniles become, the greater the chances that they will survive and mature. However, there are a couple of high risk periods in which the mortality rate spikes upwards. The first of these is the pelagic phase, which may last anywhere from a few days to a couple of weeks or more with Hippocampus erectus fry. There tend to be heavy losses due to "floaters" and "surface huggers" during this free-swimming planktonic stage of life. Losses also tend to increase during the transition phases when the juveniles are making the changeover from one type of live food to another, and especially when they are being weaned off of live foods onto frozen Mysis. Some of the fry seem to have a difficult time adjusting to such changes in their diet, and simply fail to thrive as a result. But once the juveniles have made that transition to frozen foods, their mortality rate drops again and their chances of surviving to adulthood increase accordingly.

3. there is a runt among them (his name is clifford) that is literally about half the size of the rest. he seems healthy and is eating well, just not growing as fast. should i isolate him from the others to make sure he’s getting enough to eat, or just leave well enough alone?

Its normal for a few undersized individuals to fall behind the others as the fry grow. You will notice that the fry in every brood exhibit a range of sizes (Giwojna, Jan. 1997). The largest individuals may be almost twice the length of the smallest of the fry. Such "runts" are at a serious disadvantage compared to their larger siblings primarily because their bigger brethren benefit from increased feeding opportunities (Giwojna, Jan. 1997). Not only can they swallow larger prey, they can swim further with less expenditure of energy (Giwojna, Jan. 1997). This allows them to feed on a greater range of potential prey and to capture food more efficiently than the small fry. So if you want Clifford to survive, it’s probably best to separate him from his bigger brethren so that he won’t have to compete with them for food.

Best of luck keeping up with the endless appetites of your seahorse fry and weaning them onto frozen foods as they grow. Keep up the good work!

Happy Trails!
Pete Giwojna

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