Can Goldfish and Betta Fish Eat Mealworms?
By Dr. Zubair Khalid, DVM, MS, PhD ·
Yes, goldfish can eat mealworms, and so can bettas, as long as the worms are offered in small amounts and in the right form. Mealworms are not a complete diet for either species, but they can work as an occasional protein-rich treat. The details matter, though, because dried, live, and flavored mealworms are not the same thing.
This article is educational and is not a substitute for veterinary diagnosis or treatment.
Quick Answer
- Goldfish and bettas can both eat mealworms, but only as an occasional treat, not a staple food.
- Live mealworms are safer than dried ones for most fish because they are softer and easier to digest.
- Dried mealworms can cause constipation or bloating if fed dry, so soak them in tank water first.
- Never feed mealworms that are seasoned, salted, garlic-coated, or packed with preservatives.
- If your fish eats too many mealworms and stops eating or looks bloated, stop feeding and watch closely.
Can Goldfish Eat Mealworms Safely?
Yes, goldfish can eat mealworms safely when the worms are clean, plain, and given in small amounts. Goldfish are omnivores, and they naturally eat insects, crustaceans, and plant matter in the wild. A mealworm is just another protein source to them.
The catch is portion size. Goldfish have a simple digestive tract, and a large, hard, dry insect can sit in the gut and cause bloating. A single mealworm is a big meal for a small goldfish. For a large adult goldfish, one or two small mealworms once or twice a week is plenty. For a small or young goldfish, half a worm or a tiny piece is enough.
If you keep goldfish, it helps to understand their overall diet and tank needs. Our Goldfish Care Guide: Tank Size, Diet, and Lifespan covers the basics of feeding and housing.
Can Betta Fish Eat Mealworms?
Yes, bettas can eat mealworms, and many bettas accept them eagerly. Bettas are carnivores, so a high-protein insect fits their natural diet better than it fits a goldfish's. In the wild, bettas eat small insects, larvae, and zooplankton.
The same size rule applies. A betta's stomach is tiny, roughly the size of its eye. A whole large mealworm can be too much. Cut the worm into pieces that match the size of your betta's normal pellets. Feed one small piece at a time and remove anything uneaten.
If your betta suddenly refuses food, that is a separate problem worth reading about in Betta Fish Not Eating.
Nutritional Value of Mealworms for Fish
Mealworms are mostly protein and fat, with some moisture and a small amount of fiber. That makes them a calorie-dense treat. For a fish that already eats a balanced commercial diet, mealworms are a supplement, not a replacement.
Research in farmed fish shows that mealworm meal can support growth when used correctly. In red seabream, replacing fish meal with defatted yellow mealworm larvae improved feed intake and growth, and fish fed partial replacements had higher survival after a bacterial challenge [1]. In grass carp, replacing 25% of soybean meal with yellow mealworm meal improved growth, antioxidant capacity, immunity, and intestinal health, but complete replacement caused oxidative stress and liver problems [2]. Atlantic salmon tolerated partial and full replacement of fish meal with defatted mealworm meal with high survival and no significant difference in growth [3].
Those studies used processed, defatted mealworm meal in formulated diets, not whole worms dropped into a tank. The lesson for owners is that mealworms are a usable protein source, but balance matters. Too much of a good thing can backfire.
Real Benefits for Your Fish
A mealworm treat adds protein and fat to the diet. For a betta that is a picky eater, a small piece of mealworm can tempt it to eat. For a goldfish, it adds variety. Neither fish needs mealworms to thrive if it is already eating a quality staple food.
Risks of Feeding Mealworms to Goldfish and Bettas
The biggest risks are overfeeding, choking, and contaminated or flavored worms.
Overfeeding and Digestive Problems
Mealworms are high in fat. Feeding them daily can lead to obesity, fatty liver, and poor water quality from uneaten food. In grass carp, complete replacement of a normal protein source with mealworm meal triggered oxidative stress and liver dysfunction [2]. That was a full diet swap, not a treat, but it shows that too much insect protein is not harmless.
A bloated belly in a betta is a common sign of overfeeding or constipation. If you see that, read Betta Fish Bloated Belly for what to do next.
Choking and Impaction
Dried mealworms are hard and crunchy. A fish that swallows one whole can struggle to pass it. The dry worm can absorb water and swell inside the gut, which adds to the problem. Live mealworms are softer, but a large one can still be too big for a small fish.
Additives and Seasonings
This is the most dangerous part. Mealworms sold for reptiles, birds, or people are sometimes dusted, salted, or flavored. Some products contain garlic, onion powder, salt, or preservatives. Garlic and onion can damage red blood cells in fish, and salt disrupts their water balance. Never feed your fish a mealworm product made for another animal or for human snacking.
Check the label. If it lists anything besides mealworms, do not use it.
Toxicity Concerns
Plain mealworms are not toxic to fish. The danger comes from what is on them or in them. Wild-caught insects may carry pesticides from lawns or gardens. Only use mealworms from a clean, known source.
Live vs. Dried Mealworms: Which Is Safer?
Both forms can work, but they are not equal.
| Form | Safe? | Notes |
|---|---|---|
| Live mealworms | Yes, with care | Softest option. Cut to size. Best for bettas and small goldfish. |
| Freeze-dried mealworms | Yes, if soaked | Soak in tank water for a few minutes before feeding. |
| Dried mealworms (plain) | Yes, if soaked | Hard and dry. Never feed dry. Soak first. |
| Canned mealworms | Usually yes | Check for added salt or preservatives. Rinse if needed. |
| Flavored or salted mealworms | No | Garlic, onion, salt, and seasonings can harm fish. |
| Wild-caught mealworms | No | Risk of pesticides and parasites. |
Can Goldfish Eat Dried Mealworms?
Yes, goldfish can eat dried mealworms, but only after soaking them. A dry mealworm can swell in the gut and cause a blockage. Soak the worm in a cup of tank water for five to ten minutes until it is soft, then feed it. Even soaked, keep the portion small.
Can Betta Fish Eat Dried Mealworms?
Yes, bettas can eat dried mealworms if they are soaked and cut to size. Many bettas ignore hard, dry food anyway. Soaking makes it more appealing and easier to swallow. If your betta refuses soaked mealworms, stick with its normal food.
Can Goldfish Eat Live Mealworms?
Yes, goldfish can eat live mealworms. Live worms are softer and less likely to cause impaction. The main risk is size. A live mealworm can bite or wriggle, so cut larger worms before feeding. Only use live worms from a clean, captive-bred source.
Can Betta Fish Eat Live Mealworms?
Yes, bettas can eat live mealworms, and many hunt them with enthusiasm. Cut the worm into pieces no bigger than your betta's pellet. Drop one piece at a time so it does not sink and rot in the tank.
How to Offer Mealworms Safely
Follow these steps to keep the treat safe.
- Choose plain mealworms. No salt, garlic, onion, or seasoning.
- Soak dried worms in tank water until soft.
- Cut live or dried worms to a size your fish can swallow in one bite.
- Feed one piece at a time and watch your fish eat it.
- Remove uneaten pieces after a few minutes so they do not foul the water.
- Limit treats to once or twice a week. Mealworms should be a small part of the diet, not a meal replacement.
Parts and Preparations to Avoid
- Do not feed the hard shell of a large dried worm whole.
- Do not feed mealworms that have been dusted with calcium or vitamin powder made for reptiles unless your vet says so.
- Do not feed mealworms from a bait shop unless the label confirms they are clean and untreated.
- Do not feed dead, moldy, or foul-smelling worms.
What to Do If Your Fish Ate Too Much or a Dangerous Form
If your fish ate a few extra plain mealworms, the main step is to stop feeding for 24 to 48 hours. Watch for bloating, lethargy, or floating at the surface. Many fish pass the extra food without issue.
If your fish ate mealworms with garlic, onion, salt, or other seasonings, treat it as an emergency. Move the fish to clean water if you can, and contact a veterinarian who treats fish. There is no home remedy that reverses seasoning toxicity.
If your fish is gasping, lying on its side, or has a swollen belly that does not improve, contact a vet. Do not wait several days to see if it gets better.
Safer Alternatives to Mealworms
If you want to add protein without the risks of mealworms, these options are easier on fish.
- Frozen or live brine shrimp
- Frozen or live daphnia
- Bloodworms (frozen or freeze-dried, soaked)
- Mysis shrimp
- High-quality betta or goldfish pellets as the staple
For bettas, a varied diet of pellets plus occasional frozen foods covers their needs well. If your betta is showing signs of illness, our guide to Common Betta Fish Diseases and How to Treat Them can help you spot problems early.
Limitations and When to Contact a Veterinarian
No article can tell you exactly how your individual fish will respond to a new food. Fish health depends on water quality, tank size, temperature, and the fish's overall condition. A veterinarian who treats aquatic animals can assess your fish in person.
Contact a veterinarian the same day if your fish:
- Ate mealworms coated in garlic, onion, salt, or seasoning
- Has a swollen belly that does not go down after a day of fasting
- Is gasping at the surface or lying on the bottom
- Stopped eating after the mealworm treat
- Has stringy, white, or bloody waste
Go to an emergency clinic now if your fish is upside down, has lost color, or is barely moving. These signs can mean a serious internal problem.
For routine questions about diet, tank setup, or a fish that seems slightly off, schedule a regular visit with an aquatic veterinarian. Bring a water sample and a photo of your tank.
Frequently Asked Questions
Can I feed mealworms to my goldfish every day?
No, mealworms should not be a daily food. They are high in fat and should be a treat once or twice a week at most. Daily feeding can lead to obesity and poor water quality.
Are dried mealworms bad for bettas?
Dried mealworms are not bad if you soak them first and feed them in small pieces. Dry, unsoaked worms can swell in the gut and cause a blockage. Always soften them in tank water before feeding.
Do I need to remove the mealworm's head before feeding?
You do not have to remove the head, but cutting the worm into pieces is safer for small fish. A whole large worm can be hard to swallow. Cutting it also lets you control the portion size.
Can mealworms make my fish sick?
Plain mealworms rarely make fish sick when fed in small amounts. Problems come from overfeeding, feeding dry worms, or feeding worms with added salt, garlic, or onion. Those additives can be toxic to fish.
What if my fish refuses to eat mealworms?
That is fine. Some fish simply do not like them. Offer a different treat like brine shrimp or daphnia, and keep the staple diet as the main food. A sudden refusal of all food is a different issue and worth a vet visit.
Related Articles
- Betta Fish Not Eating
- Goldfish Care Guide: Tank Size, Diet, and Lifespan
- Betta Fish Bloated Belly
- Can Cats Eat Tuna Fish
- Common Betta Fish Diseases and How to Treat Them
- Can Dogs Eat Pumpkin Seeds? Cucurbitin and Parasite Guide
References
- Replacement of Fish Meal by Defatted Yellow Mealworm (Tenebrio molitor) Larvae in Diet Improves Growth Performance and Disease Resistance in Red Seabream (Pargus major). Animals : an open access journal from MDPI, 2019.
- Yellow mealworm (Tenebrio molitor) meal in diets of grass carp (Ctenopharyngodon idellus): Effects on growth performance, antioxidant capacity, immunity, intestinal morphology, and intestinal microbiota. Animal nutrition (Zhongguo xu mu shou yi xue hui), 2025.
- Effects of Fishmeal Substitution with Mealworm Meals (Tenebrio molitor and Alphitobius diaperinus) on the Growth, Physiobiochemical Response, Digesta Microbiome, and Immune Genes Expression of Atlantic Salmon (Salmo salar). Aquaculture nutrition, 2024.