KEEPER BASICS: POND FISH

An introduction to the perfect pond fish

At this time of year, most of us will be spending much more time outside in our gardens. For some, this will mean cleaning the patio, watering the plants or giving the garden shed a much-needed lick of paint. For those with garden ponds, or ambitions to build a pond, more considerations are likely to be made about which fish they can keep and how to best care for their existing fish. In this feature, we break down some of the most popular pond fish and the specialist diets required to care for them.

Golden Rudd

Scardinius erythrophthalmus

The golden rudd, sometimes referred to as a ‘rosette’ is a silver fish with vibrant red fins. They are excellent pond fish as they are extremely hardy, interesting to watch and live well in small shoals of 10 to 15 fish. Larger groups can be maintained, but it’s important to remember these fish can grow to a reasonable size (up to 40cm) and will breed readily. They also co-habit well and will often shoal with larger fish such as Orfe. They are surface feeders and with their vibrant fins and communal feeding behaviours, can make for great observational animals. In the wild, they would typically feed on midges, damsel nymphs and other aquatic invertebrates. In captivity, an insect-based pond food such as the FishScience ‘variety pond food’ will provide an excellent food for this species.

Tench

Tinca tinca

Tench are a native species, which work extremely well in a garden pond. In the wild, they are typically found at the bottom of muddy rivers and lakes, feeding on molluscs on the riverbed. In an ornamental garden pond, this natural behaviour can be utilised to help clean the water. As they stir up sediment while they feed, the filtration system can catch any dislodged detritus and prevent build-up on the base of the pond. Two varieties are frequently available in the UK, the small, orange ‘golden tench’ and the slightly larger, iridescent ‘green tench’. Both varieties are very affordable and can add some diversity to even the most basic of goldfish ponds. Tench should be introduced in small groups and can grow over 35cm in length. Tench prefer sinking foods, but over time they will begin to surface-feed alongside goldfish and koi. Flakes, pellets, sticks and live/frozen food are all readily accepted.

Gudgeons

Gobio gobio

Gudgeons (Gobio gobio) are a much smaller alternative to tench. They are another native fish that is highly sociable, feed on the bottom of the pond (and assist filtration in the process) and can be acquired at a very low cost. Rarely growing more than 12cm, the gudgeon can be found in various freshwater habitats across Europe and Asia. Maintaining a group of gudgeons can be beneficial not just to ornamental ponds, but to wildlife ponds also. In fact, gudgeons make up almost 45% of the common kingfisher’s (Alcedo atthis) diet and over 50% of the Eurasian otter’s (Lutra lutra) diet. Although most pond fish will negatively impact native amphibians (particularly during spawning times), the gudgeon may attract grass snakes (Natrix natrix) which will frequently feed on young fish.

In a healthy pond with a rock bottom, gudgeons will actively breed throughout summer. Like tench, gudgeons prefer sinking foods but will eventually learn to take floating flakes and pellets.

Keeper Basics: Pond Fish

Orfe/Ide

Leuciscus idus

Orfe are the domesticated relatives of the European Ide. Coming from large waterways across Eastern Europe, they are some of the hardiest fish available and are capable of tolerating temperatures as low as 4°C. This being said, they do require very large bodies of water, so only the largest ornamental ponds should house these fish. Their popularity has dwindled as koi carp have taken over, but orfe can still be ideal for ponds with large surface areas but are too shallow for koi.

The water should be cool and well oxygenated (ideally with a water feature to ensure high oxygen levels overnight). Orfe also have insatiable appetites, making them unsuitable for cohabitation with smaller fish or fry. Young orfe will feed on a variety of insect larvae and therefore a well-formulated insect-based diet is extremely important for this species. The FishScience ‘variety pond food’ is comprised of two separate pellets. One of these contains high levels of carotenoids to maintain the colour of the fish, the other contains wheat germ and additional insect meal to support the fish's overall health. Combined, they offer the ideal diet for a hungry Orfe. There are several varieties of Orfe. The most widely available is the ’golden’ form, but a more recently produced ‘blue’ form and a wild-type ‘silver’ form are also available from many stockists.

Goldfish

Carassius auratus auratus

Canary yellow, comet and shubunkin goldfish make excellent additions to any ornamental pond. They are vibrant, easy to care for, widely available and will live comfortably in various-sized ponds. Goldfish can also be kept in mixed groups, meaning the keeper can have a lot of choices when it comes to introducing new inhabitants to the pond. Goldfish do prefer hard water and a deep pond will help protect them from the harshest seasonal conditions.

Goldfish produce very little waste when they are kept in a large pond (the same cannot be said for small aquariums) so they are a perfect introduction to pond fish. Even the most basic of ponds, providing it is well-maintained and built to a suitable size, will happily accommodate a group of goldfish. There are only a handful of things to consider for most hardy goldfish varieties. Firstly, females must outnumber the males as they will be chased during the summer months when breeding begins. Secondly, goldfish will breed (and interbreed) readily so the keeper must check that the pond does not become overstocked.

Koi

Cyprinus carpio

The king of all pond fishes, the koi carp is an iconic fish linked to luxury and Japanese culture. They are becoming increasingly more available and although some koi can fetch several million dollars at auction, fish keepers can obtain stunningly beautiful specimens for a similar price to many goldfish. Koi do, however, have slightly more specialist requirements. For example, they will need a much larger pond, with excellent filtration and well aerated water. Although this is not particularly difficult to achieve, it will cost more financially.

Koi are typically very hardy and will survive the UK winters easily, but should be switched onto a ‘cold weather pond food’ to aid in digestion. There are some other considerations to ensure the koi look as healthy as possible and this falls mostly down to food choice.

In general, koi cannot make their own colour pigment so they have to consume it in their diet. In the wild, these pigments would originate from eating algae, shrimps, snails etc. In the confines of an aquarium or pond, there is not enough algae or other natural supplies of pigment, so it must be included in the food that is provided. As with all foods, colour-enhancing food should be high quality to ensure that the pigments are in a form that the koi can absorb into its body. If foods containing colour enhancers are not given, the chromatophores may not be filled with pigment and the koi may look pale or poorly coloured. The colour-enhancing ingredients in fish food can either be natural or artificial, but all are a source of these pigments.

Natural ingredients which are rich in colour pigments that can be utilised by our fish include krill, spinach, spirulina algae and carrot. The addition of garlic, Beta-glucans and omega oils will also help maintain the health and vitality of koi fish, which is essential for larger high-value koi.

Overwintering

All of the fish mentioned in this feature are extremely hardy and can be kept outdoors without additional heat all year. However, they should be transitioned onto ‘cold weather pond food’ once temperatures fall below 10°C. Although this might seem like a far stretch from the weather we are currently experiencing, picking up a tub of this specialist food in preparation for winter is encouraged. Once temperatures start to fall, fish may encounter digestion problems and therefore a softer, more easily-digestible pellet with a higher protein content is recommended.