Freshwater Feeder Fish Nutritional Content

Discussion in 'Feeder Forum' started by Boidae Keeper, Aug 7, 2015.

  1. Boidae Keeper

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    Alright, so we all are tempted to feed our garter snakes and water dragons a fish or two from time to time, and for good reason. A varied diet is mentally and nutritionally superior to your run-of-the-mill crickets and mealworms, but as I've come to find, very little research has been made of the nutritional content of the whole bodies of these fish. Most of what I could find was for the human tidbits in the muscle, which was only a scrap of the information I needed. As such, I did a little bit of digging to give a more accurate nutritional makeup for freshwater fish.

    Disclaimer: All of my sources (unless otherwise stated) come from "Nutrition and Feeding of Fish" by Tom Lovell, which conducted studies on channel catfish, trout and salmon, carp, and the eel. This book was published in 1998 and is, by no means, anymore than a guide. This was the best source of information for me, and for those without access to this book, I paraphrase if here. My hope is that we can gain enough interest to do some tests on the detailed nutritional content on common feeder fish such as guppies and minnows, which are often recommended as feeders. Many people go on to claim that these are "nutrionally superior" to goldfish and rosy reds without ever providing evidence to support this claim.

    Calcium and Phosphorus

    Let's start with the meat and potatoes of meal time: the calcium and phosphorus content. A great majority of the calcium and phosphorus can be found in not only the bone tissue of fish (duh) but also in the scales. That being said, fish absorb most of their minerals through the water so if you were to gutload your guppies calcium, the most effective way to do it is to dissolve calcium in the aquarium water.

    On page 64 of Lovell's book, he discusses the calcium content very briefly, yet still manages to sum it up quite nicely for us in layman's terms. Channel Catfish contain a calcium-to-phosphorus ratio of 0.7 : 1.6, which can rule out fish as a main food source. (Exact paragraph: "Most of the calcium in the fish body, perhaps 99% of it, is in skeletal tissue and scales. Up to 20% to 40% of the total calcium is in scales. During fasting, calcium is resorbed through the hard tissue for physiological functions. The percentage of calcium in the whole, fresh (wet) bodies of finfish ranges from 0.5% to 1% with a ratio of calcium to phosphorus of 0.7 : 1.6.")

    Alright, so it's generally a bad idea to feed a lot of fish in your animal's diet, but it must have some redeeming qualities? Maybe a vital nutrient that other food sources lack, yet still proves vital to the health of your animal?


    Whole prey is a good source of protein all-around, but for the most part we tend to want to avoid an excessive amount. This is due to the fact that this type of diet can lead to gout, a serious condition due to dietary problems. The average amount of crude protein in the domnesticated adult mouse (according to is about 55.8%, rather high, don't you think? Well, a study conducted at Harvard ( suggested that 6 ounces of wild salmon had about 34 grams of protein, or about 20% protein content.

    Obviously fish is lower in protein content than mice, but not necessarily better. One mouse serves the same amount of protein as three fish, which might be better for those worrying about gout, although it won't give a carnivore its necessary amount of protein alone.

    Fat Content

    How do fish fare as far as the fat content within them? Well, according to Lovell, the total fat content in the tissue of uncooked channel catfish averaged at 8.6%, while sea-caught salmon averaged at 1.5%. The adult mouse, according to Rodentpro, averages at 23.6% in fat content. Obviously, fish are a better option here in regards to fat content.

    Vitamin A

    I've heard that fish is high in vitamin A, which is a small concern for some that dread overdoing it with vitamin a. Skimming through George Borgstrom's book, Fish As Food V2: Nutrition, Sanitation, and Utilization, I've found a nice piece of data to work with. Most of the vitamin a in the bodies of fish is stored in the liver, while a close second is the digestive tract of these animals. Freshwater fish, such as Mountain Whitefish, has a higher content of Vitamin A than brackish fish that are commonly used as feeders. Whitefish, for example, have a total amount of 63800 IU in their bodies, while Chinook Salmon has an average total of 53500 IU. Compare that to the 578,272 IU vitamin A content of the adult mouse, and even then the brackish fish would have a lower amount of vitamin a. This would probably make guppies, platies, and mollies (with beta-carotene supplements) a better alternative to purely freshwater fish, such as goldfish and minnows.

    Vitamin D

    Another vitamin that I hear a lot of in fish is Vitamin D3, an important factor in the absorption of calcium into the body. According to this article (, every 3.5oz of salmon would result in a Vitamin D content of about 400 IU. Granted, salmon is particularly high in vitamin D compared to most fish, yet most fish are still a good source of this vitamin.


    There we go, a guide to help the average keeper add a bit of variety and nutrition into their reptile's diet. By no means do I claim that the fish commonly fed to reptiles, such as goldfish or guppies, follow these numbers or percentages exactly, but rather they help to outline the nutritional content of fish overall. Fish are a healthy treat for semi-aquatic or aquatic reptiles that normally prey on them in the wild, but I do not think that these should be made a staple. They have a low calcium to phosphorus ratio, and unless you breed the fish yourself, they're likely to be swimming in diseases and parasites. I do believe, however, in the right circumstances they can be fed occasionally as they are healthy in most other regards, and can enrich your animal's diet as they provide variety that most don't offer.

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