With over 30,000 species of fish in the world, it can be challenging to decide which type of fish is best for your aquarium. Two popular choices for beginner aquarists are mollies and goldfish. If you’re wondering how these fish compare, you’ve come to the right place.
If you’re short on time, here’s a quick answer to your question: Mollies and goldfish have very different care requirements – mollies thrive in tropical aquariums with small gravel substrate, while goldfish need much larger tanks with fine substrate.
Mollies are livebearers that breed readily while goldfish lay eggs. Both fish have unique personalities but goldfish require more specialized care overall.
In this comprehensive guide, we’ll cover everything you need to know about choosing between mollies and goldfish. We’ll compare their origins, ideal tank conditions, behaviors, compatibility with other fish, breeding habits, typical lifespan, and more.
Read on to become an expert on mollies and goldfish!
Origins and Natural Environments
Mollies
Mollies originate from fresh and brackish waters of Central America, from Mexico to Panama. They are found in shallow, vegetated habitats like marshes, mangroves, and shallow streams. In the wild, mollies prefer warm water temperatures between 70-82°F.
They thrive in hard and alkaline water conditions. The three most popular molly species kept as aquarium fish are the sailfin molly (Poecilia latipinna), black molly (Poecilia sphenops), and short-finned molly (Poecilia mexicana).
Mollies are highly adaptable fish that can tolerate a wide range of water conditions. Their natural habitats have low dissolved oxygen levels and high temperatures, so they can tolerate poor water quality better than most aquarium fish.
However, optimal water parameters for mollies in home aquariums are quite different from their native waters.
In the home aquarium, mollies do best in water with a pH between 7.0-8.0, hardness between 10-25 dGH, and temperatures between 70-82°F. Adequate filtration and weekly water changes are important for maintaining high water quality.
Mollies are brackish fish, so adding a small amount of marine salt (1-2 teaspoons per 5 gallons) can help replicate their natural environment.
Goldfish
Goldfish originated in eastern Asia, where they lived in slow-moving freshwater habitats like rivers, lakes, and ponds. The first records of goldfish come from China over a thousand years ago, where they were selectively bred as ornamental fish.
Goldfish were later introduced around the world as pond and aquarium fish.
There are several different goldfish varieties, but the common goldfish is the closest to the wild ancestor. Common goldfish tolerates a wide range of water conditions thanks to their adaptable biology.
However, optimal parameters for goldfish are a pH between 6.5-7.5, hardness between 5-19 dGH, and temperatures between 65-75°F. Cold, moving water with abundant vegetation and hiding spots provides the most natural home aquarium environment.
While goldfish can survive in small tanks or bowls, a larger aquarium is highly recommended. A minimum of 20 gallons for the first fish and 10 additional gallons per extra goldfish allows them ample swimming room. Adding aquatic plants can help filter the water and provide enrichment.
Providing strong filtration and 25-50% weekly water changes will maintain excellent water quality for goldfish.
Tank Size and Setup
Minimum Tank Size
When it comes to minimum tank size, mollies and goldfish have different needs. Mollies are tropical fish that only grow to about 4 inches, so they can thrive in a 10-gallon tank. Goldfish, on the other hand, are cold water fish that can grow quite large, up to 12 inches.
Because of their potential size, goldfish need much more space and should be housed in at least a 20-gallon tank.
Water Conditions
Mollies and goldfish require different water conditions to stay healthy. Mollies prefer warm tropical temperatures between 70-82°F and need water with a pH between 7.0-8.0 and a hardness level between 10-25 dGH.
Goldfish thrive in much cooler water between 60-72°F and need a pH between 7.0-8.0 and a hardness level between 5-19 dGH. Providing the right environment is key to keeping these fish species healthy and happy.
Decor and Substrate
When it comes to tank decor, both mollies and goldfish enjoy some plants and hiding spots. Mollies particularly like dense vegetation since they are livebearers who need places to hide to give birth. Floating plants like hornwort are great options.
Goldfish may eat or uproot plants, so hardy plant species like anubias or java fern are recommended. For substrate, mollies do well with fine gravel or sand. Goldfish are prone to eating gravel and prefer a larger size substrate they can’t swallow, like large river rocks.
Behavior and Compatibility
Mollies and goldfish exhibit some behavioral differences. Mollies are generally peaceful and social fish that do well in community tanks. They like to swim in groups and will interact with each other. Goldfish also do well in groups, but can be boisterous and even predatory towards smaller tank mates.
They may chase and nip fins if kept with passive fish.
Mollies prefer planted tanks with hiding places. Having vegetation and decorations makes them feel more secure and less stressed. Goldfish, on the other hand, will often uproot plants and rearrange tank decor in search of food.
Their powerful suction feeding tends to disturb heavily decorated aquascapes.
Compatible Tank Mates
Mollies are one of the most compatible freshwater fish for community tanks. Good tank mates include:
- Other peaceful community fish like tetras, rasboras, corydoras catfish
- Similar-sized mollies
- Guppies
- Some types of dwarf cichlids
- Shrimps and snails
Goldfish have more limited options for tank mates as they can be boisterous. Suitable companions include:
- Other goldfish
- Weather loaches
- Some sturdy catfish like plecos
- Large apple snails
In general, mollies offer more flexibility for peaceful community aquariums. Goldfish require some special considerations when it comes to finding compatible tank mates.
Diet and Feeding
When it comes to dietary needs, mollies and goldfish have some key differences. Mollies are omnivorous fish that need both plant-based and meaty foods in their diet. A balanced mollie diet should include:
- Flake foods
- Frozen or freeze-dried foods like brine shrimp, bloodworms, and daphnia
- Blanched vegetables like zucchini, spinach, and cucumber
- Fresh fruit like melon and berries in moderation
- Quality spirulina-enhanced pellets
Mollies enjoy variation in their diet. Feeding them the same flake food day after day can lead to nutritional deficiencies. Varying their diet with freeze-dried and fresh foods provides important vitamins, minerals, and proteins.
In contrast, goldfish are omnivores that lean heavily towards plant-based foods. Appropriate goldfish foods include:
- Sinking goldfish pellets
- Blanched vegetables like peas, lettuce, and zucchini
- Thawed frozen foods like daphnia, brine shrimp, and bloodworms 1-2 times per week
- Quality flake foods occasionally
Goldfish don’t need as much protein in their diet as mollies. Feeding them too many meaty frozen foods can cause digestive issues. Focus their diet on fibrous vegetables, spirulina-enriched sinking pellets, and occasional treats of brine shrimp or daphnia instead.
Feeding Schedule
When it comes to feeding schedules, there are some small differences between mollies and goldfish as well:
- Mollies should be fed twice per day, once in the morning and once at night. Offer as much as they can consume within 2-3 minutes.
- Goldfish can be fed 1-2 times per day. Because they graze on vegetation in the tank, they don’t need as many dedicated feedings. Offer an amount they can finish within 1-2 minutes 1-2 times daily.
Both mollies and goldfish are prone to overeating if overfed. Feed them measured amounts at regular intervals instead of giving unlimited food. Uneaten food should be promptly removed to maintain water quality.
Here are some general feeding tips for both mollies and goldfish:
- Offer a variety of foods to provide balanced nutrition.
- Soak dry foods in tank water before feeding to prevent bloating.
- Avoid overfeeding, feed only what they can consume within a few minutes.
- Remove uneaten food promptly to avoid water fouling.
- Supplement their diet with blanched veggies for added fiber.
Tailoring feeding amounts and schedules to your particular fish helps prevent obesity and nutritional deficiencies in both mollies and goldfish.
Breeding and Lifespans
Breeding Habits
When it comes to breeding habits, mollies and goldfish have some similarities but also key differences. Both are prolific breeders that can produce hundreds of fry in a single spawn, but mollies are livebearers that give birth to free-swimming young while goldfish lay eggs.
Mollies can store sperm for up to 6 months and give birth every 60 days once mature. Females release 10-60 fry at a time. Goldfish reach maturity in 1-2 years and females lay up to 1000 adhesive eggs during spring/summer spawning seasons.
The eggs hatch in 2-7 days.[1][2] While mollies breed readily in captivity without any special setup, goldfish need particular water temps and surfaces for egg laying. So mollies generally breed more easily in a home aquarium.
Average Lifespan
When comparing average lifespans, goldfish tend to significantly outlive mollies. With proper care and room, goldfish can survive 10+ years. The common pet mollies only live 2-5 years normally. Several factors impact lifespan for both species:
Species | Average Lifespan | Lifespan Factors |
Mollies | 2-5 years | Water quality, diet, genetics, tank size |
Goldfish | 10+ years | Water quality, diet, genetics, tank size |
While mollies are short-lived, goldfish with excellent care can exceed 15-20 years.[3] Selective breeding programs for fancy goldfish have also extended lifespans over wild ancestors. So goldfish generally outlive mollies by a wide margin.
Conclusion
When choosing between mollies and goldfish for your freshwater aquarium, it’s important to thoroughly research their unique needs and behaviors. Mollies are livebearing tropical fish best suited to small community tanks.
Goldfish require much larger cycled tanks, special equipment, and dedicated care. Both fish can make fun, interactive pets but goldfish are longer-lived and have more complex requirements.
We hope this detailed guide gave you the information you need to decide whether hardy mollies or characterful goldfish are the right fit for your tank. Whichever species you choose, be sure to fully cycle your aquarium and test water parameters regularly.
With proper setup and care, mollies and goldfish can bring years of aquatic enjoyment.