Choosing and Keeping Fish: A Beginner's Buying Guide

Whether you're setting up your first aquarium or stocking an outdoor pond, choosing the right fish is about more than picking the prettiest colours. Every species has its own requirements for water temperature, tank or pond size, diet, and compatibility with other fish. Getting this wrong is the single biggest cause of early fish losses for beginners.

Before buying any fish, work out three things: how big will it grow, what water conditions does it need, and is it compatible with the other fish you already keep or plan to keep? Tropical freshwater fish generally need a heated aquarium kept at a stable temperature, marine fish need carefully maintained saltwater parameters, and pond fish need enough depth and volume to cope with UK winters and summers. Feeding is just as important as housing — the wrong fish food can lead to poor growth, bloating, or water quality problems. Take your time researching a species before you buy, ask your retailer plenty of questions, and always quarantine new arrivals where possible to avoid introducing disease to an established collection.

Freshwater Aquarium Fish

Freshwater tropical fish are the most popular starting point for new fishkeepers. Species vary hugely in size and temperament, from small shoaling fish suited to nano tanks like the Nano Curve Acrylic Fish Tank, through to larger community fish that need more swimming space. Most tropical freshwater fish need water kept between 24-28°C, so a reliable heater such as the 100w Digital Aquarium Fish Tank Heater is essential rather than optional.

Marine Fish

Marine fishkeeping is a step up in complexity and cost, requiring stable salinity, temperature and water quality, plus usually a protein skimmer and strong filtration. Species like clownfish, tangs, and Anthias are popular but need a mature, well-established tank before introduction. A dedicated setup such as a marine fish tank and cabinet set gives new marine keepers a properly sized, ready-to-plumb system, while larger collections or reef setups often benefit from a sump-based system like the 460L marine tank, sump and cabinet for extra filtration volume and stability.

Pond Fish

Outdoor pond fish such as koi and goldfish are hardier than most aquarium fish but still need adequate depth (at least 60-90cm in areas with cold winters) to avoid freezing and enough surface area for oxygen exchange. Feeding should be adjusted seasonally — a good pond fish food formulated for the season helps fish build up reserves for winter and recover well in spring.

Stocking and Compatibility

Big, showy fish like large angelfish need more space and compatible tankmates than smaller community species — mixing boisterous or predatory fish with small, timid ones is one of the most common stocking mistakes. If you're drawn to species such as Angel Fish, research their adult size and temperament carefully, as they can outgrow smaller community setups and become territorial with age.

Frequently Asked Questions

How do I know what fish are compatible with each other?

Check adult size, water parameter needs (temperature, pH, hardness), swimming level, and temperament before mixing species. Research each fish individually and avoid combining fast, boisterous fish with slow or timid ones.

How many fish can I keep in my tank or pond?

Stocking depends on adult fish size, filtration capacity, and surface area for oxygen exchange, not just tank volume. As a rough starting guide for community aquariums, allow generous swimming space per fish and always research the specific species' adult size before adding it.

What should I feed my fish?

Diet depends on species — most tropical and marine fish do well on a good quality flake, pellet, or frozen food, while pond fish benefit from seasonal formulas that adjust protein levels for warmer and colder months. Overfeeding is one of the most common causes of poor water quality.

Do I need to quarantine new fish?

Yes, wherever practical. A separate quarantine tank for 2-4 weeks lets you observe new fish for disease or parasites before introducing them to an established aquarium or pond, protecting your existing stock.