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Goldfish Feeding and Digestion

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This article will discuss how you can feed goldfish to minimize swim bladder and feeding related health issues, the amount that should be fed, and how this ties in to the anatomy of the goldfish.

Goldfish have an extremely inefficient GI tract, and are completely lacking a true stomach.

About 15% of teleosts, including cyprinids, have no stomach and no region of low pH or pre-digestion. Anterior portion of intestine has some storage function, intestine in these species is usually very long compared to, say, a trout

(Rombout, et al. 2011. Teleost intestinal immunology. Fish and shellfish immunology)

Here is a more in depth description:

Carp lack a stomach, but have a long intestine which winds extensively throughout the visceral cavity. The gall bladder rests on the dorsal surface of the anterior midgut and the bile duet opens into the intestine just anterior to the gall bladder. In addition, the liver has no specific shape, but seems to serve as packing material around the intestine. Food seems to be ingested in small particles in a relatively steady stream instead of intermittently in large units, so the storage function of a stomach probably is not missed. With the liver filling all the available visceral space, there would be no room for accommodating the stomach expansion of a large meal anyway. The remainder of the visceral organs are relatively unremarkable

(L. S. Smith. “Chapter 1. Digestion in Teleost Fishes.”
6.3 Common Carp (Cyprinus carpio)
. University of Washington, 1980)

Their odd anatomical structure has evolved out of a carp’s need to forage constantly to take up any food source they could find. This is partly why they can also be such a hardy and incredibly invasive species. But there is much to be learned from this in regards to their health and feeding habits in a domestic setting.

This is precisely why goldfish need small meals, especially fancies with their compressed body shape, which makes them more susceptible to complications caused by overfeeding. The best way to establish how much food your fish should be getting is by weighing them. It is generally accepted to feed .5-1% of the fishes body weight if feeding pellets. If gelfood is being fed, which contains much more water, you can bump this number up to 2-3%. This post on Koko’s can tell you approximately how many pellets to feed based on weight. Then take the total amount of food you’re going to feed and divide it into as many meals as possible. I try to feed my fish 3-6 times per day, but this varies with my work schedule. The key is to experiment and see what your fish do best on. Proper food management in regards to time and amount can really make a huge impact on fish with swim bladder issues and help encourage growth (in fish that are growing slowly) or discourage growth (to lessen chances of obesity). Moist foods, such as gelfoods, can often be more gentle on the GI tract than pelleted foods due to their high water content which does not expand as readily in the gut and is often more easily digestible.

Many breeders looking to groom a fish to show will feed more frequently but this does increase the likely hood of factors like obesity and often impacts the lifespan of the animal, so take into consideration that overfeeding does have consequences other than the obvious (more waste output). Overall proper amount when feeding and spreading more meals out over a given period of time will help food be constantly moving through the GI tract and in proportional amounts. This will lessen the pressure being put on other organs, the swim bladder in particular, which will aid in better balance and lower the risk of constipation.

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