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Introducing New Fish

21st Nov 2019

Adding new fish to a pond can be an exciting experience for the pond keeper, but if not managed properly can easily cause stress to the fish. Before you buy any fish, the following should be taken into account;

  • Season – it isn’t advised to re-house fish during the winter. As a general rule, the water temperature of your pond should be above 10°C. This is even more important if the fish are being moved from indoor tanks or heated vats, as a sudden change in temperature can be a massive shock to the fish. The best time of year for adding new fish is middle to late spring. Fish shouldn’t be introduced to a pond too late in the season as they will need time to acclimatise before the onset of winter.
  • Current Stock – if there are already fish in your pond they should be compatible with the new fish. 2cm goldfish added to a pond with a 1 metre koi may quickly become fish food!You should also be sure that your pond isn't currently over-stocked. To calculate the stock rates of your pond click here.
  • Pond Set-up – a 15cm sturgeon will fit snugly into a 1 metre square pond, but will soon outgrow his environment. It is important to take into account what size the fish may grow to. The size of your pond, rate of filtration, and amount of aeration should be considered for when the fish begin to grow.
  • Water Parameters – the water quality should be checked before new fish are added. The presence of ammonia or nitrite should be dealt with before adding new fish. pH levels should also be checked.
  • Increasing Stock Quantities – too many fish should not be introduced to a pond over a short period. The amount of bacteria in the filter will need to adapt to the rise in ammonia levels with the increase of fish stocks. Adding a filter start product when increasing stock rates, and reducing feeding for a few days after introducing new fish can help.

Once all the above have been checked the following introduction guide lines should be followed;

  • Transportation – When you purchase your fish they will be stored in a bag for transportation. It is important that as much air as possible is trapped in the bag, and just enough water to cover the fish’s dorsal fins. It is also vital that the fish are not over crowded in the bags.
  • Journey Time – The fish should be taken directly to their new home. The oxygen levels in the water will soon begin to drop, and carbon dioxide levels will rise within the bag. The trip should take no longer than 2 hours and you should avoid exposing the bag to bright sunlight.
  • Equalising Temperatures– Once you have reached your destination the bag can be opened and left to float on the pond. It may need anchoring so that it doesn’t float out of reach. Folding the bags edges down will trap a ring of air to aid buoyancy.The bag should be floated on the pond for around 30 minutes, allowing the temperatures to equalise.
  • Equalising Parameters – Small amounts of pond water should be added to the bag for up to an hour. This allows the fish to get used to any slight variances in the water chemistry.
  • Releasing Fish – The fish can then be carefully released into the pond, tipping the bag onto its side and letting the fish swim into the pond. The bag and any excess water can be discarded.

The new fish will probably hide almost straight away, and may not be seen for a few days. Some species may also jump; Grass Carp and Orfe can be especially skittish when relocated. It may be necessary to use a cover net or to drop the level of the water.