When it comes to deciding what to feed your goldfish, there are many options on the pet store shelves. But how do you know which is the best for your fish?
Before you grab whatever package looks best on the fish store shelves, you need to take a close look at the ingredient label. All pet food labels contain a guaranteed analysis statement and list of ingredients. If you cannot find these on the package of goldfish food, do not buy it.
The guaranteed analysis is a measurement of the various macronutrients in a food product. By U.S. law, fish foods are required to list the percentage of moisture, protein, fat, fiber and phosphorus. Any additional listings are at the discretion of the company.
Ingredients are listed by the highest percentage in a diet to the smallest amount. Some companies list out specific vitamins and minerals, while others will list these as a "vitamin premix." Both are valid.
What should I look for in a goldfish food?
When choosing a food for your goldfish, follow these guidelines:
Pellets vs. Flakes
It is always best to feed your goldfish pellets, rather than flakes. Pellets come in various sizes, so you will likely find one that is appropriate for the size of your fish. Flakes have a higher surface area to mass ratio, meaning they will float better than pellets, but goldfish that eat food at the surface may ingest air, and round bodied goldfish such as orandas may develop floating disorders. Pellets tend to slowly sink and your goldfish can eat them while they drop and will even eat them off the bottom of the aquarium. If you do use flake foods for your goldfish, you can hold the pinch of food under the water surface to release it, so the goldfish eat it while it is falling, rather than floating at the surface.
Fish food should be kept in sealed containers in cool environment and used within one to six months of purchasing the food container. If kept longer, the vitamin content may decrease in the food. Flake food may spoil faster than pelleted food, and lose moisture. Water-soluble vitamins, such as vitamin C—which is critical for proper immune function—decreases faster in flakes than in pellets. If you store fish food in the refrigerator or freezer it will keep fresh longer. Do not leave food out in the sunshine or at high temperatures if using it for pond fish.
Protein is the main source of energy for fish. Carbohydrates are not well processed and a diet high in carbohydrates can lead to liver damage. For goldfish, a maintenance level around 30% is recommended based on current research. Juvenile goldfish and those individuals involved in breeding should be fed a higher level, around 35%.
Feeding a higher protein diet will lead to a fast growing fish and lots of nitrogenous waste. Despite common myths, goldfish do not "grow to the size of their container," and rather are stunted due to poor diet and water quality. Your goldfish can easily outgrow their small tank on a high protein diet. Lots of protein in the diet leads to additional ammonia production, which can seriously impact your aquarium or pond's nitrogen cycle. Goldfish should start in an aquarium of at least 20 gallons, but will likely need more room as they grow.
It is also critical to count the number of protein sources in an ingredient list on the food label. This may take some extra research on your part, but higher quality diets will have fewer protein sources. Fish require from their diet ten essential amino acids (arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine) in order to live. This may take just a few protein sources to supply, usually from fish or shrimp meal, or if other protein sources are used, some amino acids may need to be supplemented. If you see any amino acids listed by their pure form, usually "L-" or "DL-," this indicates the usage of cheap protein sources. There is nothing wrong with these diets, just don't shell out top dollar for lower quality protein in the food.
Unless your fish is a growing juvenile or an adult actively making baby fishes, they do not have a high fat requirement. Rapidly growing fish use oils over protein or carbohydrates as their primary energy source. The fat in the diet should be supplied by unsaturated fats, usually fish oil. Anything higher than 5-8% fat in the food is not necessary for adult goldfish and significantly higher levels can impact liver function.
Fiber is the carbohydrate portion of the fish food. Fish do not utilize much carbohydrate in their natural diet. A goldfish's digestive system is not acidic like ours, so their ability to digest fiber is extremely limited. High fiber is of no benefit to your fish and should be avoided. Usual amounts of fiber in the fish food should be no more than 20-30%.
How Often Should I Feed My Goldfish?
How often you feed your goldfish is dictated by your aquarium water temperature. Most goldfish aquariums will hover around 72-76 degrees Fahrenheit (22-24C) in a typical home, unless you live in a colder area, or use an aquarium heater in your tank. Goldfish do NOT require a heater and too warm of water temperature may excessively increase metabolism. Ideal water temperature for goldfish is 68-75 F (20-24 C), but they can live in a wider temperature range than that.
General guidelines for goldfish feedings per day are relatively flexible. In the lower 70s and down into the 60s (less than 23 Celsius), feed your goldfish once per day. Above this, you should feed twice a day. Do not feed more than your fish can eat in a few minutes. Sprinkle very small amounts and once that has been completely consumed, sprinkle a little more for up to 3-5 minutes at each feeding.
How Do I Know If My Goldfish is Overfed?
Goldfish are prone to obesity like many other pets. However, an overfed goldfish can be hard to differentiate. Body condition scoring is a common method of determining if a pet is overweight. While there are good standards for other fish, such as zebrafish, there is no set standard for goldfish.
Using the zebrafish research, a simple goldfish obesity test can be applied. Looking down at your goldfish, their head and pectoral girdle should be the widest part of their body and then taper gradually to the tail. If your goldfish gets wider right behind their pectoral fins, they may be overweight. However, this may be normal for a reproductively active female goldfish. Fat vs. eggs can be easily determined on ultrasound. Also, round bodied goldfish varieties always look fat in the middle!
What Can Happen If Your Overfeed Your Goldfish
If you overfeed your goldfish, they are at risk for obesity, may quickly outgrow their aquarium and it will create water quality issues. Obesity causes strain on internal organs, as it does in other pets. Thankfully, fish have to continuously swim, decreasing the risk, but it is still a concern.
As stated previously, overfeeding can quickly increase the size of your fish and cause them to need tank upgrades relatively quickly. This can also lead to an increase in ammonia output and strain your beneficial bacteria in the biofilter that manage the nitrogen cycle. And high ammonia can lead to fish health issues and death.
Dietary protein requirement of juvenile golden shiners (Notemigonus crysoleucas) and goldfish (Carassius auratus) in aquaria. Aquaculture. 1994;128(3-4):277-285.
Clark TS, Pandolfo LM, Marshall CM, Mitra AK, Schech JM. Body condition scoring for adult zebrafish(Danio rerio). J Am Assoc Lab Anim Sci. 2018;57(6):698-702.