How to Determine the Sex of your Goldfish

Although goldfish were never my favorites, I appreciate the classic, simple beauty and joy involved in keeping a school of these diverse, colorful creatures. When I talk to goldfish owners, many of them are eager for me to help them identify the sex of their fish. It is, of course, easier to name and relate to a pet if you can refer to it as "he" or "she" and give it a gender-appropriate name.

It can be difficult to accurately determine the sex of a goldfish. Unlike some fish, such as guppies and bettas, goldfish exhibit very limited sexual dimorphism-- they don't display obviously different characteristics depending on sex. However, it is possible to determine whether your goldfish is male or female. Here are some methods you can use to find out your goldfish's sex.

Shape

Male and female goldfish have slightly different shapes. Male goldfish are usually longer and thinner, with a more torpedo-shaped appearance, when compared to females of the same age and variety. Females, in general, are rounder and thicker, with more flesh around the abdomen.

Behavior 
Male goldfish tend to chase other fish, particularly females, and may nudge the females' rears after catching up to them. If you notice that one fish is almost always the chaser, and that the other is usually the "chasee," odds are good that the more aggressive fish is male and that the victms are female. However, this is not a universal rule; sometimes species gender roles will be obscured in a tank with few males or few females.

Vent Area and Anal Fin 
Look at the goldfish's vent area, near the anal fin. A female goldfish's vent will protrude very slightly beyond her abdomen, appearing as a raised surface beneath her belly. Her anal fin will also look marginally thicker than the anal fin of a male goldfish. By comparison, a male's vent area will completely flat, and its anal fin will appear thin.

Midline Ridge

If possible, look at the underbelly of the goldfish to determine its sex. A male goldfish has a "midline ridge," or a raised line that extends from the back of the pelvic fins to the vent. The ridge is either completely absent or very faint in females. Unfortunately, it can be difficult to look at a goldfish closely enough to examine for signs of the midline ridge.

Tubercles

When ready to spawn, male goldfish develop small white spots on their gill-shields, known as breeding tubercles. Not all males exhibit breeding tubercles, but, when they do appear, they are a certain sign that the fish is male. Tubercles may last for several days or weeks, depending on the male's maturity and biology.

A goldfish's sex is usually irrelevant unless you specifically intend to breed your fish. However, many fishkeepers find it inherently enjoyable to give their pets gender-specific names and projected identities. If you are able to do so, you may find it well worthwhile to determine the sex of your goldfish.

Best Fish for a Cold-Water Aquarium

If you want a small or low-maintenance aquarium, you may be considering forgoing the heater and operating your aquarium at room temperature. Unless you select new aquarium fish with cool temperatures in mind, you can expect tropical fish to meet an untimely death from living in an inapporpriate environment.

The following common, readily available fish species can surprisingly low water temperatures without it comprimising their long-term health. Although the choices for stocking a cold-water aquarium are limited, many beautiful and active species of fish are available to choose from.

Rosy Barbs

A member of the minnow family, Cyprinidae, the rosy barb is one of the most cold-tolerant of tropical fish, and has been selectively bred to accentuate this feature. They are fun, beautiful, and very suitable to community aquariums, so long as no long-finned or slow-moving tankmates are present. Rosy barbs can live at temperatures as low as sixty degrees before it begins to weaken them.

Guppies

While the guppy is a tropical fish that requires warm water to thrive, some well-domesticated strains of guppy will do quite well at lower temperatures, sometimes as low as seventy degrees. They are quite hardy and forgiving, making them especially ideal for first-time aquarists. Their small size makes them especially suitable to miniature cold-water fish tanks.

White Cloud Mountain Minnows

Another popular, hardy addition to a small home aquarium, the petite and gem-like White Cloud is a pleasant and easy-to-keep fish for cold-water aquariums. They are native to extremely wintry environments and some aquarists claim that they can even survive freezing (but please don't test this!). The White Cloud Mountain minnow's coloration grows duller at temperatures below the seventies, but it remains hardy even in the fifties.

Zebra Danios

Zebra danios, like guppies, are tropical fish that have been selectively bred for thousands of generations, resulting in dozens of distinct strains. Most of the domesticated strains of zebra danio are quite tolerant to cold waters, and can stay tough and active at temperatures in the mid-sixties. They are very easy to care for, petite, and suitable for a small tank.

Bloodfin Tetras

An active, feisty top-feeding fish, the bloodfin tetra is very hardy and lives well in cold-water tanks, including community aquaria. It is readily available in most pet stores and can tolerate temperatures as low as sixty degrees, and it remains beautiful and strong even in unideal circumstances and do best when kept in groups of five or more.

5 Reasons Not to Buy a Goldfish

I have been keeping freshwater fish for over a decade, and people who know me are often surprised to find out that I don't own goldfish-- and that I never have. Goldfish are often imagined to be easy-to-care-for, healthy, enjoyable pets, but there are few serious aquarists who keep them. Here are five good reasons not to buy a goldfish.

Goldfish Need too Much Space.

The image of a goldfish in an unfiltered bowl is persistent, but these cruelty-pots can't accommodate a goldfish for more than a few days-- or, at most, a few weeks. Let's face it: goldfish aren't suited to live in bowls, or even most aquariums. The goldfish is excellent as a resident for an outdoor pond, but even small goldfish require extensive room for swimming, several same-species companions, and stable water chemistry. A planted, twenty-nine gallon aquarium is the bare minimum for keeping a healthy population of goldfish.

Goldfish Poop. A Lot.

I have often referred to goldfish as "the cattle of the aquarium". They spend most of their time eating plant-based food and then defecating, so even a large aquarium with an excellent filtration system can barely keep up with their waste output. A goldfish aquarium will often develop cloudy water, nitrate pollution, or an offensive odor due to the high waste output from these little golden poop-dispensers. New fishkeepers are often surprised to learn how filthy goldfish actually are.

Goldfish are Hard to Maintain.

A goldfish's waste output doesn't end with its feces. Goldfish also produce massive amounts of nitrate and ammonia, but they require a relatively clean living-space with high levels of dissolved oxygen. This means that a goldfish aquarium will require excellent filtration, frequent water changes, gravel-vacuuming, and constant water-testing. For all that effort, you might as well opt for a large tropical community tank, which would give more variety with less trouble.

Goldfish are Unsuitable for Community Tanks.

Many aquarists make the mistake of keeping goldfish in community aquariums, with other fish species. This can sometimes work out, but it more often leads to chaos. Goldfish are cold-water fish, so they can not survive long in a heated tank-- and tropical fish can not survive long in an unheated tank, either. Goldfish can also be territorial and aggressive toward other fish. Additionally, many community fish are sensitive to the high waste output that goldfish provide. Still, a few species can be compatible with goldfish: this list offers a few cold-water species worth considering.

Goldfish are Overrated.

There are hundreds of species of ornamental freshwater fish on the market, and almost none of them cause as much trouble as goldfish. Rosy barbs, zebra danios, and several strains of tetra are available in long-finned and golden-colored forms, and they tend to be both hardier and cleaner than goldfish. Compared to many varieties of ornamental fish, even the most ostentatious of goldfish appear drab. Do yourself (and your pets) a favor, and avoid buying a goldfish unless you have experience keeping them.