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Horse Forum - July 2001

by Dr. Clyde Tamaru and Carol Cozzi-Schmarr
from the July 2001 issue of Freshwater and Marine Aquarium magazine (FAMA)

I would like to thank Chris Burns for his contributions to the last 3 columns and formally introduce my next guest speaker Dr. Clyde Tamaru. You may recognize his name from the many truly impressive sea horse photos in the previous columns.

Clyde is an Aquaculture Specialist with the University of Hawaii Sea Grant Extension Service. Dr. Tamaru was born and raised in Hawaii were he received his BS and MS from the University of Hawaii at Manoa. He later received his Ph.D. from the Laboratory of Reproductive Physiology in Fishes, University of Tokyo in Japan. He has been engaged in the development of hatchery technologies for marine food fish species for over 20 years. Since 1995 he has been engaged in the expansion and diversification of the freshwater ornamental fish industry in Hawaii.

We are honored that Clyde, a man of so many talents and expertise, has offered to share his knowledge with the readers of FAMA through Sea Horse Forum. In this issue Clyde will be answering questions about sea horse physiology and sea horse growth. In the August column he will be focusing on sea horse anatomy which is one of the most intriguing and poorly understood aspect of the sea horse. Charles Delbeck, a legendary aquarist, will be following Dr. Tamaru as the next guest speaker so please send your questions for Clyde and Charles right away to [email protected] so that our special guests can select the best questions and provide you with excellent answers!!!

Mahalo, Carol Cozzi-Schmarr

Clyde,

I would like to buy a pair of juvenile giant sea horses that are currently about 3 inches tall. I thought that I would put them in a 16 inch tall tank that I have ready right now, and later switch them over to a taller tank. I have been told that the aquarium should be 3 times the height of the sea horse and that the giant sea horses can grow to be 8 inches tall so I need to find a tank that is at least 27 inches tall since I plan on having 3 inches of substrate in the bottom. This will take me a while to find the appropriate tank and set it up the way I want it. How fast do sea horses grow? Will their growth be slowed down in my aquarium??? How long do I have before I need to put the sea horses into a taller tank? How long can I expect them to live if I care for them properly??

Thanks, William

Dear William,

The answer to this fundamental question (How fast do they grow?) is also important to both the biologist and aqua-culturist but difficult to obtain from wild sea horse populations. However, when fish are in culture it is relatively easy to obtain the changes in body weight in relationship to a fish's age. The ability to culture these animals also provides the opportunity to obtain information about certain aspects of the life history of these creatures that otherwise would be very difficult, if not impossible, to obtain.

When the data is summarized graphically a growth curve can be obtained during the culture process and one is presented in Figure 1 for farm-raised sea horses. The dotted line shown in the growth curve represents the average body weight (g) for each age group. As can be seen from the graph the rate of growth is relatively slow during the first three months of their life. It increases dramatically and begins to slow again after they reach sexual maturity just like in humans. Because the data was obtained from cultured sea horses the question that remains, "Is this what happens in nature?" The one thing about science is that answering one question only leads to more questions. There is something else that can also be done with the data and that is a statistical model can be generated: BW= (0.047*Day)-1.353 where BW = the body weight in grams and Day = age of the individual. The statistical model is the simplest of models (linear model) but provided a relatively good fit of the growth data. The slope of the line calculated using the statistical model provides a rough estimate of another important parameter about the biology of the sea horse and that is how fast they grow (0.047 grams per day). The calculated rate of growth is relatively slow compared to other aqua-cultured species and illustrates one of the constraints that faces entrepreneurs trying to culture these fishes commercially. Another mystery is how long do sea horses live? At this point in time all that can be added is that these farm-raised sea horses are over two years of age with an average body weight of 40 grams and still producing babies!! We will just have to be patient to obtain the answer to that question.

Regarding your question on whether or not the growth of your sea horse will be inhibited in your aquarium, any fish, including a sea horse, can be inhibited to grow in captivity depending upon a number of factors (e.g., size of the aquarium, amount of food, number of other fishes, number of other sea horses). Overcrowding is usually a major factor but if your aquarium is large enough there should not be any problems. What is large enough? The only time we start to see stunting of growth in fishes is during intensive culture trials. For example, our work with intensive culture of swordtails we find that at densities above 4 fish per gallon of water stunting occurs. If you think that your sea horse in your aquarium is not growing, in most cases the sea horse you purchased from the pet store is likely a wild-caught adult individual that is already sexually mature and their rate of growth is already slowed down immensely or may have even stopped. This is an inevitable part of the growth process in vertebrates. If it is a farm raised sea horse and you know that it is a young adult you can look forward to the sea horse growing quite a bit more but very slowly. As far as when to move the young adults to the taller tank it would be ideal to have your new and taller tank ready for the new arrivals from the very beginning, but I if that is not an option I would be ready to move your sea horses to the new tank as soon as possible.

Dear Carol,

I have 4 sea horses and 6 cleaner shrimp in my tank which is in my office so I can look at them all the time. I have noticed that sometimes the cleaner shrimp spend a lot of time walking all over the sea horses. Sometimes the horses violently object to the cleaning and jerk away. Is this behavior something to worry about? Do I have too many shrimp in the tank? Should I take them out? I would hate to cause any harm to my sea horses as I am really quite attached to them.

Dear Harry,

These cleaner shrimp are actually doing the sea horses a great clean up service! The best thing to do is enjoy the show and let them do their job!

The shrimp are scavengers by nature and will eat most types of small organisms from bacteria to algae to small invertebrates like copepods. The skin of the sea horse is often full of various harmless critters that the shrimp will graze upon providing the shrimp with extra nutrition. Occasionally the skin of the sea horse may be invaded by harmful critters and these will hopefully be grazed down to a manageable level by the shrimp so that no harm is caused to the sea horse and once again the shrimp get a good meal!

Dear Clyde,

I have never understood why the male sea horse is called a male when he not only carries the babies but even gives birth to the babies! Why shouldn't the one that carries the babies and goes through labor be called the female?

Thank you,

Patricia

Dear Patricia,

The dictionary's definition (Webster's Unabridged) of the male sex is, "of or belonging to the sex that begets young by fertilizing the female". The ability to fertilize the female or in the sea horse's case her eggs distinguishes the male from the female and not who carries the eggs. Therefore, believe it or not, even though the male carries all the babies and "does all the work" he is the he!!

Dear Carol,

Just a curious question. To cycle my Sea Ranch, I have added 4 small pieces of live rock. Today, several weeks after adding the live rock, I noticed very tiny (and I emphasize the word tiny) white creatures swimming and crawling on the tank walls. Any ideas what these might be?

Dave

Dear Dave,

These little critters are most likely copepods. They obviously hitched a ride with the live rock and are thriving in their new environment. Although there are a few species of copepods that can be harmful to sea horses the great majority are not. In fact, most copepods are a favorite food for the sea horse and this population explosion will be a real treat for the sea horses!!!

Dear Dr. Tamaru,

My male sea horse has given birth three times to a lot of baby sea horses. I have spent hours watching them chase each other around in the most incredible mating dance I have ever seen. Never, though, have I seen the actual passing of the eggs by the female to the male. Have you seen it? How does it actually happen?? Will I ever be able to see it??

Thanks, Elias

Dear Elias,

I have yet to see the transfer myself but do remember that there was a program on TV a year or so ago that had actually captured it on tape. What was most memorable was that while the courtship ritual can be a prolonged process the transfer of eggs occurs very quickly (blink of an eye) and the recording had to be slowed down to see the process unfold. I believe it was a documentary of the work being done by Amanda Vincent in her Project Sea Horse but am not fully sure. The transfer has also been described by Neil Garrick-Maidment (1997) Sea Horses, Conservation and Care, where after a courtship ritual the female will place her "ovipositor" into the male and transfers the eggs in a few seconds. The process is not always perfect though as I have seen eggs on the bottom of the tank from passes that were not completed correctly. I suspect that if you are very lucky and keep watching you might catch a glimpse. Good Luck!

Dear Carol,

I was told that I should separate my male sea horse from the female when he is pregnant so that I can easily collect the babies and prevent the parents from eating the babies. My instincts tell me that splitting up my mated pair will cause them both to be really stressed. Won't he miss his mate? Will they really eat their own babies??

Thank you, Natasha

Dear Natasha,

Your instincts are right. Separating the male from the female will cause a great deal of stress to both the female and the male with the greatest harm being done to the male. In fact, it can stress the male so much that you may put him into shock and run the risk of loosing him.

First, fish in general, do not like to be moved to new habitats. That in itself is a major stressor and should be avoided. Like most animals they are most comfortable being in a familiar environment which includes sleeping in the same spot, having the same tank mates and knowing the details of all the nooks and crannies in their habitat.

Second, sea horses are very social and curious animals. They have daily rituals, which consist of greetings and displays and all kinds of wonderful behaviors that are not only very enjoyable to watch but a necessary part of their nature. These behaviors are how they communicate with one another and part of this includes informing each other that it is time to mate. This helps the pair to synchronize their biological clocks enabling them to bond so that they can produce sea horse fry routinely. This innate drive is so strong that the male will usually re-mate with the female immediately after he spawns or gives birth to the baby sea horses. If he is in a different tank the couple will not be able to continue their daily bonding rituals and may not re-mate at all.

Although other fish will, adult sea horses will not eat the baby sea horse fry. If you want to collect the sea horse fry, the easiest thing to do is to net them out of the parent's tank.

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