UNIT 17Understand the Principles of

Aquatics Husbandry and Management

1. Breeding strategies

Sexing Fish

Most fish are sexually dimorphic or sexually isomorphic. In dimorphic species, the sexes can be easily distinguished. Males are often colourful and larger with more elaborate fins.

In sexually isomorphic species, there are minute, if any, apparent differences.

In some isomorphic species, the males are slightly larger and the females are slightly rounder in the belly. But some sexually

isomorphic species have no known external sexual differences. Sometimes there will be clues in the fishes’

behaviour; sometimes you just have to mix up enough fish to ensure you have boys and girls in your spawning group.

Breeding strategies

ParentsIf males and females can be distinguished, choose a suitable pair or spawning group.

These should be mature, colourful, healthy, and have no deformities.

In some species the males and females must be introduced carefully or one partner may

bully the other.

Breeding strategies

Conditioning the Parent FishBefore putting any parent fish together for spawning,

they should be conditioned.

To condition the fish they are fed a variety of healthy foods. This could be as simple as a quality flake food, but more often live foods such as brine shrimp, tubifex, daphnia,

and earthworms.

Sometimes the parent fish are separated while they’re conditioned. When they are reintroduced, they are often

eager to spawn.

Breeding strategies

Conditioning foods

Brine shrimp; tubifex worms; daphnia and earthworms.

Breeding strategies

Egg-layersMost of the tropical fish that your

clients will keep are egg-layers. They lay eggs by: scattering; depositing in one area; burying the eggs; building

nests or mouth-brooding.

Breeding strategies

Egg-scatterers: These species simply scatter their adhesive or non-adhesive eggs to fall to the substrate, into plants, or float to the surface. These species do not look after their brood and even eat their own eggs. These, often schooling, fish may spawn in groups or in pairs. Often there is a large number of the small eggs laid. The fry hatch quickly.

Breeding strategies

Egg-depositors: These species deposit their eggs on a surface (tank glass, wood, rocks, plants). They usually lay fewer, larger eggs than egg-scatterers. Some egg-depositors care for their eggs, some don’t. Egg-depositors include cavity spawners and open spawners. Cavity spawners lay their eggs in a cave, the others lay their eggs on an open surface. They usually form pairs and look after the eggs and fry. The egg-depositors that lay their eggs against a surface, and promptly abandon them. These species do not usually eat their eggs.

Breeding strategies

Egg-buriers:

Some species come from waters that dry up during the year. Fish like the short-lived annual Killifish mature in a few months and lay their eggs before the water dries up. The eggs remain in a dormant stage until rains stimulate hatching.

Breeding strategies

Breeding strategies

Mouth-brooders:

Some fish carry their eggs, larvae and fry in their mouth.

They are ovophiles or larvophiles.

Breeding strategies

Ovophile (egg-loving) fish lay a small number of eggs in a pit, then they’re sucked up into the mouth of the female.

The eggs hatch in the mother's mouth, and the fry remain there for a period of time.

Fertilisation often occurs with the help of egg-spots, which are colorful spots on the anal fin of the male. When the female sees these spots, she tries to pick up the egg-spots, but instead gets a mouthful of sperm, fertilizing

the eggs in her mouth. Many cichlids and some labyrinth fish are ovophile mouthbrooders.

Breeding strategies

Larvophile or larvae-loving mouth-brooders lay their eggs on a substrate and guard them until

the eggs hatch. After hatching, the female picks up the fry and keeps them in her mouth.

When the fry can fend for themselves, they are released.

Breeding strategies

Egyptian mouthbrooder

Breeding strategies

Nest-builders: Nest builders build some sort of nest for their eggs.The nest is

usually in the form of bubble-nest formed with plant debris and saliva-coated

bubbles (labyrinth fish, catfish).

Nest builders practice brood care.

Breeding strategies

LivebearersLivebearers are fish that bear live young. There

are two types of livebearers: ovoviviparous, where the eggs form and hatch within the female before birth; and viviparous, where no eggs are

formed, and the young are nourished through an umbilical-like cord or from secretions

by the female.

Livebearers are often prolific, easily-bred species.

Livebearers

A pair of Black mollies.

2. Helping fish breed

Some species will spawn frequently in the aquarium, but the eggs or fry do not survive because they are eaten by

the parents or other fish.

Sometimes the fry die because of poor water conditions.

In addition, many species that practice brood care will harm other tank mates as they attempt to guard the eggs. Because of all these problems most fishkeepers who regularly breed fish use a separate spawning tank.

Helping fish breed

There are many different styles of spawning tank. The aquarium should contain water from the same tank the parents are in, and this should be tested for ammonia and nitrates. You need a mature filter – that is one that

has a healthy population of filter bacteria already – which has a gentle action. Otherwise the eggs or fry may be

sucked up; and good aeration. Depending on the spawning method, the spawning tank can be set up in a

number of different ways.

Helping fish breed

A breeding tank for egg-scatterers:

Egg-scatterers often eat their own eggs, so the spawning tank has to be set-up so the eggs fall safely out of the reach of hungry parents. A 23 to 46 litre tank is usually

large enough. Some egg-scatterers like barbs and danios lay non-adhesive eggs. For them the tank can be

furnished with a substrate consisting of two layers of glass beads, marbles or a nylon netting just above the

tank floor. The eggs are fall through between the marbles or the mesh netting. After spawning is over, the

eggs or the parents can be removed.

Helping fish breed

Other egg scatterers lay adhesive eggs. The spawning tank should be furnished with a clean

sandy substrate. Then the tank should be planted with fine-leafed plants. The eggs are laid

among the plants, and stick to the leaves. The parents should be removed after spawning.

Rainbowfish also lay adhesive eggs, but most species spawn continuously over several weeks.

The eggs or the plants that the eggs are attached to should be removed daily and placed

in a rearing tank.

Helping fish breed

A breeding tank for Egg-depositors

Some egg-depositors that care for their young, so the parents can remain in the tank after spawning. Substrate spawners, depending on the species, should be given a tank furnished with glass panes, broad-leafed plants, or

flat stones for suitable spawning sites.

Some species such as Discus and Angelfish prefer vertical surfaces.

Cave spawners like flower pots turned on their side, so coconut shells, and rocky caves are suitable spawning sites. The tanks should be furnished with either live or

plastic plants to give the fish a sense of security.

Helping fish breed

Egg-depositors that do not look after their young, should be given a tank furnished with fine and broad-leafed

plants, Java Moss, or artificial spawning mops.

After spawning either the parents or the plants with the eggs should be

removed.

Helping fish breed

Egg-buriers

Some fish, such as killifish, as we’ve already seen, bury their eggs in the substrate. A peat-moss

substrate works well. It’s then carefully removed after spawning and stored in a plastic bag for weeks to months (depending on the species).

Then to initiate hatching, the stored peat can be immersed in soft water.

Helping fish breed

Mouth-brooders

Some mouth-brooders can be bred in the main aquarium because the eggs are

protected in their mouths. However they can be aggressive to other fish so it may

be better to separate mouth-brooders with eggs. There are no special breeding tank requirements other than the usual healthy

tank set-up for the species.

Helping fish breed

Larvophile mouth-brooders should be placed in a breeding tank because the eggs are not protected in the mouth, but laid out in

the open where they are vulnerable to predators.

Helping fish breed

Nest-builders

Nest-builders should be provided with material with which to build their nests.

For bubble-nest builders, fine leafed and floating plants should be provided, and the tank should have very little

water movement to disturb the nest.

Species that build nests in the substrate should be given fine gravel or sand.

Helping fish breed

Livebearers

Small livebearers can be bred in breeding traps where the newborns

fall out of the reach of the mother. As soon as all the young are born,

remove the mother.

Helping fish breed

Stimulating SpawningOne of the best ways to get fish spawning, especially difficult-to-spawn species, is to

simulate natural conditions.

Things that encourage fish to spawn are the environment, the food, and the rainy

season.

Helping fish breed

Water Conditions

The right water conditions are among the most basic requirements in spawning fish. Thus the

water conditions should be similar to those in the natural environment of the species.

The right tank to match the natural habitat will include hiding places, spawning sites, lighting, water current, and social conditions (schools).

Helping fish breed

Food

The right foods are important to encouraging spawning. Without proper foods, natural conditions cannot be entirely recreated.

Helping fish breed

Simulating the Rainy Season

Many fish species spawn during the rainy season in nature. Simulate the rainy

season and difficult-to-spawn species can be induced to spawn.

We need to make a thunderstorm

Rain affects the water chemistry, the water height, and the water temperature. Freshwater dilutes pollutants in the river and freshens the water. To make a thunderstorm:

1. Reduce the holding tank level to half its normal height.

2. Daily add 5% of the tank volume, using soft cool water.

3. To simulate rain, use a spray bar for a few hours a day.

4. Simulate storms by flashing lights in a dark room....

5. Play a recording of thunder...

And believe it or not some people actually do all this... The storm process can be repeated until the fish show

signs of spawning preparation.

Helping fish breed

Add target or dither fish

"Target fish" can be used to help strengthen the bond between a fish pair. A target fish is placed in the tank with the breeding pair and serves as

a target for the aggression of the pair. They’ll work together to chase off the target fish and not

fight between themselves. Only use the target fish method in a large tank with plenty of hiding

places, so that the target fish is not harmed.

Helping fish breed

Rearing Tank When species take care of their young these are less

important. But when species don’t care for their young, the rearing tank can be re-used (as long as the parents are removed). The rearing tank should have a heater, a gentle filter, and plastic or real plants. Cover three of the

tank sides with black paper, because light can encourage fungal infections and stress the fry.

The water in the rearing tank should be similar to the water used for spawning.

Helping fish breed

Raising the frySmall livebearers can be easily recognised but when eggs hatch, the larvae that emerge look nothing like the parents. They have a large yellow yolk sac and are barely able to move, let alone swim. They feed off the egg sac until the yolk is gone, then begin to look

for food. The fry can be fed infusoria and/or green water, then larger foods like whiteworms, Daphnia, Artemia nauplii, and ground flake. These foods are also good as a first food for slightly larger fry such

as those of cichlids. Once the fish grow larger, larger foods like brine shrimp, larger Daphnia, flakes, insect larvae, and chopped Tubifex worms are accepted. The fry should be fed several times a day.

Helping fish breed

Between 25-50% of the water in the rearing tank should be changed daily with "new" water that closely resembles the water taken out as fry are very sensitive to sudden

changes in the water chemistry.

With favourable water conditions, regular water changes, and generous feeding, the fry should grow quickly.

Many species need periodic sorting by size, so that larger fish do not cannibalise smaller fish.

• http://www.waterzoo.co.uk/Fishkeeping%20videos-U21

• https://www.youtube.com/user/KGTropicals/videos

• Danios http://animaldiversity.ummz.umich.edu/accounts/Danio_rerio/