Grindal Worms

Grindal Worms


Grindal Worms
By: Roger Winter

Grindal worms are probably one of the most important cultivated live foods available for both marine and freshwater fish. They have the advantage of being cheap and easy to cultivate, highly nutritious and they cannot harbour any aquatic disease or pests. They are greedily taken by day old fry to large adults of all species and aid in the growth of new born livebearers. First isolated from white worm cultures by Mrs Morten Grindal of Sweden who was very active in the methods of culturing white worms. About half the size of white worms 3/16 - 3/8 inch 0.5 - 1 mm long they are related to earthworms and are normally much more prolific than white worm. Each individual worm contains the organs of both sexes and they reproduce in a manner similar to the earthworm, two worms lay side by side with heads pointing in the opposite directions, the worms then secrete mucus and when they are covered in a tube of slime an interchange of sperm is effected. Each worm will now lay eggs so reproduction is fairly rapid. White worms and Grindal worms occur naturally in soil but a culture is best obtained from a livefood supplier (several have web pages see the links page) whom normally advertise in the small ads in the back of aquarium publications or from a fellow aquarist who has a culture established.

Before we discuss the method of culture of these worms it should be pointed out that they do have a few disadvantages. Some aquarists feel that fish fed exclusively on Grindal worms become obese due to the fat content of the worms, I have never had any problems in this area as I do not feed exclusively on worms. I suspect the problem lies more with the aquarist overfeeding on worms which are highly nutritious and the fish which are permanently half starved in the wild become sated and do not exercise by constantly swimming looking for food, rather that the fats in the worms. Another problem is that the worms although they can live several days immersed in water cannot swim and so sink to the bottom were they will dig into the gravel if present to escape the light. No problem in bare bottom tanks were all will eventually eaten or siphoned out, nor in tanks with catfish, loach or snails as these will actively hunt down and devour every worm present. Dead worms can soon foul a tank so do not overfeed in tanks were large quantities of surplus worms will foul the gravel bed. Grindal worms are light and strong airation will keep them in circulation in the water for some time or alternatively use a worm feeder to feed the fish as few escape the fishes attention this way. The last problem is that often non aquatic partners often find the presence of these worm objectionable in the house, (they are completely harmless by the way) either cultivate them in a shed or garage and allow for reduced or non production over the winter months or better still put said partner in the shed or garage thus freeing up more room in the house for tanks.

Grindal worms can be cultured in plastic boxes from 250 gram size up to the shallow two litre ice cream tubs. Obviously the larger the container the longer the culture should last and remain fresh and productive. The container should be washed and sterilised and have a tight fitting lid. Pin holes to allow an exchange of air within the culture, can be either pierced in the lid, or as some culturists insist around the periphery of the container itself as they maintain this inhibits the fouling of the culture by flies. The container should now be two thirds filled with a suitable medium for the worms to live in. The worms do not like acid soil and peat is too acid unless well boiled to leach out excess acids, various other mediums such as sterilised garden loam, African Violet soil, bulb fibre and leaf mould are all used by various aquarists to culture worms in, each having his own preferred medium. Indeed this is one area were experimentation is worth doing to find out what the worms you have prefer. In nature the largest concentration of worms are found in well rotted vegetable matter as this is a source high in food. I have had the most success with leaf mould from a local beech wood that has been used to farm earthworms in for a year prior to being sterilised and used for the Grindal worms, using it fresh failed to obtain good results, and the most success with multi-purpose potting compost (peat based) from garden centre’s used straight out of the bag. The compost should be damp, too damp and the culture will die off and smell rather badly, too dry and the worms will burrow deep into the soil and slow down reproduction. The right degree of dampness is when the medium can be shaped into a ball that retains its shape but crumbles into small clumps of material as soon as it is touched with any pressure. Many different foods have been recommended for Grindal worms and commercial food is available, the most universally accepted and most successful food is instant porridge (Readybrek™ in the UK) and on the initial setting up of a culture a teaspoon to tablespoon dependant on the size of the culture should be mixed in with the culture medium to encourage the worms to spread throughout the medium. These instant oats normally have vitamins added which will pass into the worm and then into the fish. Now introduce a portion of worms onto the surface of the medium and cover the surface of the medium with polythene leaving a quarter inch gap all around the edge of the polythene and the edge of the container to allow the medium to breathe. Do not feed the culture at this point except by placing a half or quarter of a boiled potato with the skin still on into the medium. The skin only should be exposed to the atmosphere to avoid the growth of mould. All worms shun the light and the containers should be kept in a shaded position, Grindal worms prefer more warmth than white worms and a temperature of 680F /200C to 750F / 240F is required for them to reproduce. Examine the culture daily to ensure that the food has not gone mouldy or all been eaten. If the food has been eaten then sprinkle a thin layer of instant porridge over the surface of the soil and replace the polythene. If all the food has gone the next day then sprinkle slightly more than previously over the soil if it has not then do not feed but examine until all the food has gone before feeding again, remove any food that is developing mould as this will ruin the culture. Once the culture is well established when you remove the cover the surface of the medium will be covered with worms and when lifted the polythene will be covered with worms that can be scraped off with tweezers or similar and fed directly to the fish. Cultures should be fed daily and an established culture should be harvested every day as this seems to encourage the worms to breed. Should the culture start to dry out the surface of the medium should be dampened either by a fine spray or better still by a tablespoon to egg cup full of water poured into the centre of the medium, this gives the worms an opportunity to find the level of moisture they prefer to deposit the eggs in before it permeates throughout the medium. It often occurs that you will get a population explosion of worms after this treatment. Unlike microworms a completely dried out culture cannot be restarted by the addition of water and must be thrown away. Food should be applied dry, whilst wet feeding often appears to get better results this only occurs for a short time before the culture needs renewing. Any mouldy food should be removed and badly soured cultures cleaned as described for mites below.

Culture sometime become infested with what are called mites, these little white insects of about a millimetre in length are normally springtails which occur naturally in soil. They do not affect the worms but do compete with them for food and sometimes reach alarming proportions. If badly infested simply dump the culture into a container of water and stir vigorously, most, but never all, the mites will float to the surface and poured off. I always pour of through a fine mesh net and dump the contents into the tanks as surface feeding fish soon find and devour them. The remaining water and soil mixture is then poured through a fine mesh net or nylon stocking and squeezed dry before being replaced into the container, it will normally take three or four days for the culture to come on line. I have kept cultures going in a 250gm plastic fish food container for over two years by only using dry food and the occasional wash and dry in a fine net.

Never rely on just one culture but set up two or three just in case you lose a culture for some reason, some aquarists set up sufficient cultures to fed one day and rest the next, this is advisable for white worms but Grindal worms seem to reproduce more quickly if used and fed every day. Once you have a culture going setting up new ones is a snap, simply set up the container and medium as above then sprinkle food on the surface and take the worm covered polythene from the active culture, replace with a new piece and place the worm covered one on the surface of the new culture. The old culture will be ready to be used again the next day and the new culture in only two or three normally.

Other infestations do sometimes occur like little red spiders and fruit flys and occasionally maggots from flies laying their eggs through the holes in the lid. All can safely be fed to the fish but in the case of bad infestations it is sometimes more practical to start a new culture free from pests. Sink the culture in shallow water so that about half an inch of water is above the level of the soil. After a while the worms leave the soil and form balls on the surface of the soil from were they can be collected, thoroughly rinsed and used to start of a new culture. Dump the old culture medium. If you have any favourite food recipes or culture mediums or methods for Grindal worms please let me know so that I may put them on the pages for all to share.

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