Fish are sometimes seen as a low-maintenance starter pet, but RSPCA guidance takes a rather different view: fish keeping can be extremely rewarding, but it’s a genuine responsibility, since fish have very specific needs and require constant attention and routine care, much like any other pet.
Understanding what your fish actually need
One of the central points in RSPCA guidance is that welfare needs vary considerably between fish species, and understanding your particular fish’s needs is essential to keeping them happy and healthy. Fish are broadly categorised by where they naturally feed and swim within the water column:
- Surface feeders — species that primarily feed near the water’s surface.
- Mid-water feeders — species that spend most of their time and feeding activity in the middle depths of the tank.
- Bottom dwellers — species adapted to feeding and living near the substrate.
Mixing species with very different natural behaviours and space requirements into the same tank without research can create welfare problems, from competition for food to outright incompatibility, which is why RSPCA guidance emphasises researching a specific species’ needs before purchase rather than assuming general “fish care” applies uniformly.
Fish are social — but selectively
Contrary to the image of a solitary goldfish in a bowl, RSPCA guidance notes that many fish are social creatures that thrive on the company of other fish. However, this doesn’t mean any combination of species works well together — some fish are territorial, some prey on smaller tank mates, and stocking levels that are too high for a tank’s size create stress and poor water quality regardless of species compatibility. Guidance on keeping pet fish together is worth reviewing carefully before adding new fish to an existing tank, rather than assuming more fish is simply better.
Recognising healthy versus unwell fish
Because fish can’t communicate distress the way a dog or cat might, RSPCA guidance highlights the importance of learning to recognise signs of good health, and equally the signs of common diseases and health issues, so that problems can be caught and addressed early. Signs to watch for typically include changes in swimming behaviour, appetite, colouration, or physical marks on the body — a marked change from a fish’s normal baseline behaviour is usually the clearest early indicator that something needs attention.
Seasonal care: fish needs change too
RSPCA guidance specifically addresses winter care, noting that as temperatures drop, the needs of pet fish can shift — for outdoor pond fish in particular, colder water affects metabolism, feeding requirements and activity levels, and care routines need to be adjusted accordingly through colder months. This is a reminder that fish keeping isn’t a “set up once and leave” arrangement, but requires ongoing, seasonally adjusted attention much like any other pet.
Basics for anyone starting out
For a beginner considering fish as a pet, sensible starting points based on RSPCA-aligned welfare principles include:
- Research the specific species you’re interested in before buying anything, including their adult size, since many fish sold small will outgrow a starter tank.
- Set up and properly cycle a tank before introducing fish, rather than adding fish to a brand-new, unestablished tank.
- Choose a tank size appropriate to the species and expected stocking level, not the minimum size that seems adequate for the fish’s current small size.
- Learn the basics of water quality testing, since poor water conditions are one of the most common underlying causes of fish health problems.
- Plan for ongoing costs and time — filtration maintenance, water testing and feeding are all recurring commitments, not one-off setup tasks.
This is a starting overview rather than a complete species-by-species care guide — given how much welfare needs vary between species, researching your specific intended fish in detail before purchase remains the single most useful step for a new fish keeper.
Why fish welfare is easy to underestimate
Part of why fish welfare gets overlooked compared to cats and dogs is that fish communicate distress far less visibly to an untrained eye — there’s no whining, limping or obvious change in posture to alert an owner that something is wrong. This makes routine observation genuinely important rather than optional: taking a few minutes regularly to actually watch your fish’s behaviour, rather than just glancing at the tank while topping up food, is one of the more effective ways to catch early signs of stress, illness or water quality problems before they become serious.
Tank size and stocking density deserve particular attention here too. A tank that looked appropriately stocked when fish were young and small can become significantly overcrowded as they grow to their adult size, and overcrowding is a common underlying driver of poor water quality, stress and disease outbreaks in home aquariums. Researching a fish’s eventual adult size — not just its size at the point of purchase — before deciding on tank size and stocking levels avoids one of the most common welfare problems new fish keepers encounter.