Re:Tube feeding

Pete Giwojna

Dear Carol:

Outstanding! It sounds like you did a remarkable job of treating your stallion and then administering the tube feeding, Carol. By all means, if you can perform the tube feeding while the seahorse remains in the main tank and you look through the aquarium glass, that’s a fine way to proceed!

Yes, it is important to avoid overloading the seahorse when tube feeding, Carol, since they lack a true stomach for storing food in quantity. It’s important to monitor how much of the gruel you are injecting when tube feeding so that you don’t overdo it, rather than just observing the seahorse’s abdomen to see if it’s "plumping" up. This is what Dr. Marty Greenwell from the Shedd Aquarium recommends in that regard:

"At Shedd Aquarium, anorectic syngnathids are tube fed a high quality, commercial fish flake food gruel. Because of the very small, vestigial stomach, only limited volumes of gruel can be administered at any given time, i.e., 0.05 to 0.10 cc for most seahorses and up to 0.25 cc or more for the large Hippocampus sp., trumpetfish, and the sea dragons. Offering nutritional support can mean the difference between survival and death in sick and/or anorectic syngnathids (Bull and Mitchell, 2002, p24)."

In other words, about 0.10 cc or mL is the right amount of gruel to inject for an average seahorse, whereas a large specimen may be able to handle up to 0.25 cc or milliliter per feeding.

My new book includes a chapter on seahorse anatomy and the following excerpt from the book will explain why it’s important to avoid overfeeding a seahorse at any given meal, Carol:

<Open quote>
Stomach & Intestinal Tract

The seahorse intestine is basically a continuous, convoluted tube leading from the esophagus to the anus, whose primary purpose is the absorption of nutrients from digested food. Hippocampus does have rudimentary stomach, but it is greatly reduced, a common characteristic of carnivorous fishes adapted for feeding continuously on small prey items (Tamaru, Aug. 2001). It is little more than a pouchlike expansion of the intestine that begins in the crook of the neck. The pylorous region of the seahorse’s stomach, which separates it from the rest of the intestine, is underdeveloped and lacks the strong, muscular sphincter that separates the two organs in humans and most other animals (Tamaru, Aug. 2001). As a result, food passes continuously through this simple stomach and it cannot store food between meals. Due their inactive lifestyle, seahorses do not need to stockpile energy in fat reserves or food stores, so this simple stomach ordinarily serves them well.

Like other carnivorous fishes, the intestinal tract of the seahorse is also relatively short (Tamaru, Aug. 2001). This fact, combined with the lack of a true stomach, combines to render their digestion very inefficient when they have an overabundance of food. Once a seahorse is full, there comes a point when it cannot take anything more in at one end of the digestive tract (the esophagus) without passing something out the other end (the anus). This sometimes presents a problem in captivity when rearing the babies, since the feeding instinct is so strong in seahorse fry that they do not stop eating once they’ve reached their full capacity. They will continue to gulp down food as long as prey is present, forcing them to eliminate food that’s only partly digested (Warland, 2003). When provided with too heavy a feeding density, this can reach the absurd point where they are passing live Artemia in their feces, and the ravenous fry can literally starve to death in the midst of plenty (Warland, 2003)!

On average, the total length of the digestive tract in seahorses, including the esophagus, simple stomach and intestines, is contained in two body lengths of the individual (Tamaru, Aug. 2001). By contrast, herbivorous fish typically have very long intestines measuring ten times the length of their bodies or more (Tamaru, Aug. 2001). They need the extra length in order to break down and absorb the hard-to-digest plant matter. (As omnivores, the human intestine stretches 20-some feet, or about 4 times our body length.)

It’s interesting to note that the male seahorses have an intestine that’s 50% longer than that of females (Tamaru, Aug. 2001). The extra food absorption ability and digestion this provides is necessary in order for breeding males to churn out brood after brood and sustain the metabolic demands of the developing fry they carry.
<Close quote>

Best of luck keeping your stallion well-nourished until it can recover from the weak snick and resume feeding on its own normally again, Carol.

Pete Giwojna

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