UNIT 17 Understand the Principles of Aquatics Husbandry and Management

Natural feeding Most of the tropical fish that we keep will do perfectly well on a diet of correctly formulated fish food – flake or some sort of pellet or granule. We have seen how these are made and the various types. We also saw that live or frozen natural foods are also useful. Sometimes they are essential.

Natural feeding Live or other natural foods are good for: Improving colours of fish Getting them into breeding condition Treating digestive problems Improving water quality Feeding “difficult” species (as an example, most seahorses will only eat specific live foods). Fish with very specific feeding techniques.

Natural feeding In the USA it is common to feed live fish (especially goldfish) to predators and there are a lot of nasty videos online which almost glory in this. In the UK this may be construed as illegal and, is usually seen as unacceptably cruel. Virtually every predator can be persuaded to eat dead foods, and often they will learn to take carnivore pellets and pieces of larger fish or prawns. There is also always the possibility that live fish will carry diseases. Frozen irradiated food or fish or invertebrates from marine sources fed in freshwater virtually eliminates this risk.

Natural feeding To help us understand fish behaviour and natural feeding strategies, let’s look at some aquarium species (and one other) with unusual ways of feeding and behaviour. Why might we need to cater for them specially and can we really do it?

Archerfish Archerfish are sometimes kept in specially designed aquaria. They are found in the brackish waters of Australia (no exports allowed from there) Indonesia, India and the Philippines. They can grow up to 25cm - females are smaller than males. They may live 10 years in an aquarium. They need a large planted aquarium at around 23C, with brackish water ie two teaspoons of marine salt mix per gallon. They are often fed locusts, crickets and other insects, but will eat flake and small live fish if they can get them.

Archerfish Archerfish are happy in shoals.

Archerfish And their unusual feeding behaviour? They lurk just beneath the surface under low lying vegetation. When a fish sees the characteristic silhouette of an insect through a leaf it moves into position. A powerful jet of water shoots from its mouth, knocking the insect into the water. Within just 50 milliseconds of it landing, it can have the insect in its jaws.

Archerfish aquarium Archerfish are best kept in a tall aquarium with room at the top for them to feed naturally on live insects. They will do this by knocking them off branches by squirting water at them... Some fish keepers may dust crickets with a vitamin powder supplement. Is there a problem if we don’t provide this feeding to match their natural behaviour?

Archerfish aquarium Feeding in action: gc0I

Snail eating puffers A freshwater species, the Dwarf pufferfish, (Malabar puffer, Pea puffer or Pygmy puffer) Carinotetraodon travancoricus, comes from the River Pamba in Kerala, Southwest India. It only reaches 22 mm making it one of the smallest puffers in the world. Although closely related to marine pufferfish, they are not found in brackish or salt water. The dwarf puffer regularly eats tiny snails and can be useful in controlling snail populations. Other larger puffers – the South American pufferfish Colomesus asellus and the two Asian green bottle pufferfish Auriglobus modestus and Auriglobus silus - will also eat snails.

Snail eating puffers The tiny Dwarf Puffer

Snail eating puffers Why is it important to feed Puffers the right food? Puffers teeth grow constantly. In captivity puffers rarely eat as much crunchy food as they do in the wild, and their teeth can grow faster than they are worn away. Puffers have teeth fused together into a beak-like structure and powerful jaw muscles. These are strong enough to crush snails and crack crab shells, and their teeth are constantly being eroded. To compensate their teeth grow continuously, and can become overgrown. In extreme cases this makes it impossible for them to feed. Live shell-on snails can help. Some fishkeepers feed the snails vitamin-rich flake food prior to use. Why?

Snail eating puffers Unfortunately puffers are often greedy and lazy and prefer soft food if it’s available (including the fins of their tank mates - puffers are best kept in a single-species aquarium.) As a result puffers sometimes need professional tooth care. Overgrown teeth are trimmed back using nail clippers or an electric saw. They are often sedated for this, which is a tricky process as the same chemicals are also used to euthanize aquarium fish...

Snail-eating puffers moC5lCA&feature=youtu.behttps:// moC5lCA&feature=youtu.be

Detritivores and hippos A number of large species (also kept in aquaria) such as Distichodus sexfasciatus coexist closely with Hippos in Africa. Fish have evolved to take advantage of this in several ways when feeding. Hippos visit cleaning stations and signal by opening their mouths wide. They then let fish remove parasites. Secondly they stir up the river bottom as they walk which releases food items. Finally the hippos poo in the water which enriches it and produces more food - but they also pass through food items and the fish have learned to follow them to feed. All a bit difficult to recreate in aquaria...

Detritivores and hippos

Distichodus Distichodus are a large growing peaceful African species that may co-exist with Hippos. They can reach 30cm plus in aquaria. Length from mouth to anus gives a clue to diet

A lesson from the Distichodus A clue to a fish’s diet is the proportional distance from the mouth to the anal fin. If the distance is long, it indicates a long digestive tract and that the fish probably has plant matter in its diet, since plants are more difficult to digest and require a longer digestive tract. D. sexfasciatus has a long digestive tract and is known to eat plant matter. But it also eats worms and crustaceans, and its sub-terminal (under-the-snout) mouth indicates it is probably also a bottom-feeding detritivore. In nature they eat fruits and seeds. In the aquarium, they will eat flakes, pellets, freeze-dried, and frozen foods.

Detritivores and hippos mmes/p004y3c5

Mississippi Paddlefish Mississippi or American Paddlefish used to be caught for their caviar-like roe and are now endangered. They can live 50 years and grow to nearly 200lb. This strange looking primitive fish Polyodon spathula was sometimes kept in aquaria. Now it never is.

Mississippi Paddlefish Young paddlefish "bite" at small food particles, but within a year as they grow and need more nutrition they switch to filtering for food. They eat large zooplankton called Leptodora kindtii Adult paddlefish swim with wide open mouths and filter zooplankton from the water with filament- like gillrakers. Sometimes this includes aquatic insects and, occasionally, tiny fish. Other species in this family (notably in China) feed only on other fish.

Mississippi Paddlefish

What’s that frontal paddle for? Research shows that it is an electro-sensory structure that detects weak electric fields. (Remember the Elephantfish?) The paddle, its head and gill flaps are covered with tiny sensory pores that it uses to detect food organisms. The paddle also keeps the fish level in the water while feeding, also providing "lift" much like an aeroplane wing. Obviously it would very difficult to feed such a fish in an aquarium.

Mississippi Paddlefish q9mhrrw

Malawian mbuna Last session I mentioned “aufwuchs” and asked you to quickly research them. Why are they important? An example is the cichlids of Lake Malawi and Lake Tanganyika which browse on the aufwuchs Feeding the right food and the right way to feed these cichlids in aquaria has been controversial. An example we’ll come to in a moment is Tropheus moori from Lake Tanganyika.

Aufwuchs Aufwuchs are the bio-cover that grows on rocks, tough strands of algae. Attached to these are "loose aufwuchs” that contain other algae, but also microorganisms like insect nymphs and larvae, crustaceans, mites, snails and zooplankton. Different fish specialise in certain items. Unlike the outer walls of plant cells which are tough, diatomic algae are broken down very easily by special teeth in the fish. Even then many algae cells remain intact even after the food passes through the fish. Fish that take a lot of nourishment from the algae have much longer intestines to allow more time to digest this food.

Aufwuchs Even in some of the seemingly most "herbivorous" of fish, growth is dependent on the proteins (live animals) found in the aufwuchs, and not necessarily on the algae at all. But the length of the intestines in some species limits the amount of proteins that can be broken down safely and this can cause bloating. It’s important to feed these fish the right balance of food.

Aufwuchs Two species illustrate this. Labeotropheus species in Lake Malawi have a low under-slung well-developed jaw that allows them more leverage in grazing the aufwuchs. They completely strip the algae from the rocks and are close to being purely vegetarian. A vegetable flake or pellet is sufficient food. Labidochromis species feed off the same aufwuchs but they pick out the insect nymphs and larvae. A general flake food will do. In between are many species that go from almost completely herbivorous, to omnivorous, to nearly completely carnivorous, yet all use the same aufwuchs as their food source.

Aufwuchs Aufwuchs feeder

Malawian mbuna As a specific example, another cichlid Tropheus moorii is completely herbivorous. The species spends the majority of its time scraping algae from the rocks or the glass in aquaria. They like shallow clear water because the light promotes algal growth. Some fishkeepers use extra lighting to encourage algal growth, but T. moorii will eat it faster than it will grow. Supplementing their diet with lettuce and spinach is a good idea, as is using a vegetable flake with a high content of Spirulina. Other foods seem to bloat the fish. It’s near impossible to set up an aufwuch environment in an aquarium so the right feeding is essential.

Malawian mbuna Tropheus moorii

Piranhas Not all of the 30+ species of the South American piranha family (Serrasalmina) are meat eaters but the famous Black and Red piranhas very much are. They can be found shoaling in the Amazon basin, and many other South American river systems. Piranhas are not large fish reaching 14 to 26 cm. All meat eating piranhas have a single row of sharp triangular teeth in both jaws.

Piranhas

Piranhas Piranhas have a reputation as ferocious meat- eating predators that hunt their prey in schools. In fact they are timid fish and should be kept in a small shoal or they will hide all the time. They may even play dead. In the wild they are a favourite food of otters, river dolphins, crocodiles and even cormorants. In the TV series River Monsters presenter Jeremy Wade swam in a tank of piranhas.

Piranhas That said (and seen), attacks may occur. In 2011, an 18- year-old man was attacked and killed in Rosario del Yata, Bolivia. In 2012, a five-year-old Brazilian girl was attacked and killed by a shoal of P. nattereri. In 2011, a series of attacks in the Brazilian state of Piauí resulted in 100 people being injured. According to a study, piranha attacks peak in the dry season when food is scarcer and the water levels are low, leading to heavier than usual concentrations of fish in the water. Most attacks take the form of nips and bites to feet and hands. Splashing makes piranhas more likely to attack, and children are often attacked for this reason.

Piranhas Factoid: Research has shown that piranhas may even eat vegetable matter at some stages in their lives; they are not strictly carnivorous fish. (Equally the “vegetarian” Pacu – a close relative famous for eating fruit and nuts - will eat meat.)

Piranha aquarium Secure lid! Hiding places Thin layer of gravel for easy cleaning... Huge external filter Plants in pots Keep piranhas in shoals

Piranhas Aquarium feeding In the USA it is commonplace to feed live fish to piranhas. However this cruelty is not necessary as they will take other meaty foods such as frozen irradiated fish, shrimps, krill and squid. A very good filter system and lots of water changes using a gravel vacuum are essential. It figures that piranhas are best kept in a shoal on their own. Even then they may eat the weakest fish in the shoal...

Piranhas Aquarium feeding This video shows how the piranha is both a messy fish to keep and essentially shy HdQ This is a longer documentary about the fish V-3I

Feeding and a healthy aquarium With any fish, leftover food should be removed as soon as possible. Meaty foods are very polluting producing a lot of protein which is converted to ammonia. In addition, fish like piranhas are messy eaters. Oscars (a large-growing cichlid) are equally bad with a habit of crushing pellets and other foods with their mouths open. Both fish will need a really good external filter system, and you will have to set-up the aquarium accordingly.

An aquarium for meat eaters Should be as large as possible (water volume). Should be easy to clean – so just a very thin layer of substrate and an open plan. (But) may need caves or other hidey holes, both for the meat eater and any companions. May need plants or wood. Should only contain carefully selected species. May need extra aeration. May need a protected heating system. Will need a very efficient large filter.

An aquarium for vegetarians May need bright lighting to grow plants and algae. Will need tough plants. Usually plants in aquaria need either to be in pots or in a deep substrate for their roots. May need open swimming space as most vegetarian species are shoaling. May not need such a large filter.

Water changes Meat eaters will need lots of large water changes – up to 50% a fortnight – and a gravel vacuum should be used to clear out any trapped wastes. The water should be tested every few days. We’ll deal with safe siphoning later in the course.

Next week More about fussy feeders and feeding techniques for aquarium fish.