Full Grown Comet Goldfish: Size, Appearance, Price & More

Comet goldfish are one of the largest varieties of goldfish. But did you know just how big they can get when fully grown? In this guide, we'll cover everything you need to know about size, appearance, care needs, costs and more for comet goldfish at their full adult size.

Size at Full Growth

When comet goldfish reach maturity, they can potentially grow over a foot in length. The maximum size range is usually 10-12 inches, but some specimens have been documented reaching up to 18 inches!

For tank size requirements at full growth, plan for at least 30-50 gallons per fish.

Weight at Full Growth

The weight of a fully matured comet goldfish depends on its size, but on average males tend to max out around 1-2 pounds, while females can reach up to 3 pounds at their largest.

Proper feeding and care is important to prevent obesity, but a healthy specimen at its peak size typically falls within this weight range.

Appearance at Full Growth

As comets mature, their colors often become more vibrant and pronounced. The classic orange/red/white coloration remains, but the scales take on a shiny, iridescent sheen. The dorsal and tail fins enlarge proportionately to the body size.

Females generally have a rounder "comet" shape compared to males which have sleeker torpedo-like bodies.

Personality at Full Growth

Goldfish are known for their curiosity and playfulness. These personality traits remain even as comets reach adulthood. They may become more bold and energetic, swimming constantly around a large tank.

However, the larger size also means comet goldfish can be more peaceful and tolerate tankmates better than juvenile fish.

Price

A fully grown comet goldfish will command a much higher price than juveniles. Expect to pay $15-30 each depending on quality of breeding and unique color/size attributes. High-quality show specimens may sell for up to $50-100 each for breeders and enthusiasts.

Food/Feeding

The food needs of fully grown comets are substantially greater than young fish.

Adults should be fed 2-3 times daily and their portions increased 50-100% over juveniles.

A variety of nutritious foods should be offered such as flakes, pellets, frozen bloodworms or brine shrimp, and vegetables like zucchini and spinach.

Lifespan

Comet goldfish have the potential to live 10-15 years when properly housed and cared for as they reach maturity. However, the larger body size and metabolism of adults means water quality must be rigorously maintained.

Daily partial water changes are recommended to support their longevity.

Health at Full Growth

Some health issues more commonly affecting fully grown comets include: obesity from overfeeding, organ failure from poor water quality, tumors/lumps, bacterial/fungal infections, and age-related decline.

Caregivers should monitor parameters closely and watch for any abnormalities, separating sick fish for treatment as needed.

Care and Nutritional Needs at Full Growth

The tank size, filtration capability, and maintenance schedule must all be adjusted to suit an adult comet's expanded requirements:

• Tank size: Minimum 30-50 gallons per fish, ideally 50-100+ gallons for one large specimen
• Filtration: Canister or sump filter rated for 2-3x the tank size
• Heating: Water temperature 74-82°F
• Water changes: 30-50% weekly for optimal health
• Enrichment: Plenty of hiding places, plants, driftwood
• Feeding: Varied, nutrient-dense diet as described above

Costing

Keeping a fully grown comet goldfish is more expensive due to the substantial tank size needed. Estimate the following ongoing costs:

• Tank purchase or build: $150-500+ depending on gallons
• Filter: $50-150 for canister or sump unit
• Heater: $15-30
• Substrate/decor: $40-100
• Chemicals/maintenance: $10-20 per month
• Electricity: $5-15 per month to run equipment
• Food: $10-20 per month for high-quality diet

Possible Behavioural Changes of a Fully Grown

Some comet goldfish may become more bold and active in a large aquarium as adults. Others may act reserved and territorial about their space. Observe any changes in:

• Activity level - Constantly swimming or restful?
• Interaction with tankmates - Peaceful coexistence or aggression?
• Feeding responses - Eagerly takes all food or selective eater?
• Environment needs - Require hiding spots or open swimming areas?

Notable Characteristics of a Fully Grown

Here are a few distinguishing traits you may notice in a mature adult comet goldfish:

• Larger dorsal/tail/ anal fins compared to body size
• Deeply pigmented eyes rather than juvenile almond shape
• Developed abdominal area below dorsal fin in females
• Shapely torpedo body type in males, rounder form in females
• Iridescent golden/red/white scales catch the light beautifully