Guppy

Guppies are peaceful, active and almost endlessly curious. They live in loose groups rather than tight schools, drifting apart to graze and coming back together when something interesting appears. A group gives a tank a sense of constant, gentle motion, with males showing off and females working steadily along the plants.

Male guppies are the show-offs of the species. They court almost continuously, spreading their fins and darting around females in short, hopeful bursts. Competition between males is mostly display, and serious aggression is rare. The real risk is exhaustion for a female who never gets a break, which is why keepers aim for two or three females per male.

Females are calmer and far more interested in food, and they generally live longer than males. Guppies are not territorial and usually ignore other peaceful species, though they will chase smaller fish away from food and can be nipped by larger or faster tank mates. Their interest in people is learned rather than affectionate: they quickly connect a face or a hand with feeding and will follow movement along the glass. Guppies are also remarkably tolerant of a busy household: they ignore footsteps, vacuum cleaners and kitchen noise, and they settle faster than most small fish after a water change or a tank move.

Male and female guppies look so different that beginners often assume they are two species. Males are smaller, usually about 3 to 4 cm, with slim bodies and large, brightly patterned fins. Females are longer and rounder, reaching 5 or 6 cm, and are mostly silver-grey with color usually limited to the tail.

The male's anal fin has become a gonopodium, a narrow rod used to deliver sperm, and his body carries the color that made the species famous: oranges, reds, blues, greens and blacks arranged in spots, snakeskin patterns, cobra markings or shimmering metallic patches. Fancy strains add huge delta, fan or lyre tails, and hybrids with the closely related Endler's guppy are common in shops.

Females show their condition clearly. A mature female has a dark gravid spot near the rear of her belly, and as fry develop she becomes deep-bodied and squared off. Wild-type guppies are modest in color, so if you want a particular look, buy from a breeder who can show you the parents rather than picking fish at random from a mixed tank. Whatever the strain, the practical difference is size and fin length: heavy tails need gentler current and a little more space, while short-finned types tend to be the most active.

A guppy group is one of the friendliest introductions to fish keeping. The fish are small, peaceful and visible, they come to the front of the tank for food, and children can watch the whole life cycle, from courtship to tiny fry, without any special equipment. A 10 to 20 gallon tank suits a small group, and the routines involved are short. Adults are the easiest fish in the house to care for on a busy day: no walking, no grooming and no noise, just a small daily job that takes two minutes.

Day-to-day life is simple: two small feeds, a look at every fish and a weekly water change. The complication is reproduction. A single female can produce dozens of young every month, so a mixed group needs a plan for the fry, whether that means a separate raising tank, a natural balance among plants and adults, or rehoming the extras.

Guppies do best in warm, hard, alkaline water, between 22 and 26C (72 to 79F) and pH 7.0 to 8.2. They are not suited to cold water, to an uncycled new tank or to a bowl, and they must never be released outdoors, where they can establish wild populations and compete with native species. Given a cycled filter, a heater and a little patience, they are among the most rewarding first fish available.