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Archives (2003) : Fisheries

Microworms: The perfect live feed for grouper fry
by Junelyn dela Rosa

January-March 2003
Volume 5 No. 1

A new feed alternative for fry or larvae of the orange-spotted grouper (Epinephelus coioides) is the microworm (Panagrellus redivivus). Microworms are tiny, nutritious and easy to culture hence, are better substitutes for the commonly used rotifers (B. plicatilis) and brine shrimp nauplii which require more labor and have become increasingly expensive to produce.

Microworms are free-living nematodes measuring 0.5 to 2.0 mm in length and 0.05 mm in diameter. Since they are very small, microworms can be fed to fish that are too small to take a brine shrimp nauplii. They are white, unsegmented and move continuously. The tail end is pointed while the mouth end is more rounded. They multiply easily in vast numbers and live for six to eight hours in freshwater, by which time they should all have been eaten.

Microworms reproduce sexually. The males have a curved tail, are smaller, more slender, and less numerous than the females. Microworms are very prolific producing 10 to 40 larvae every 1 to 1.5 days for a 20 to 25 day life span. On the average, each female produces 300 young. The young sexually matures in three days and grow three times larger during the first day and five to six times larger in the next three days.

It has the same or more nutrients than Artemia nauplii containing 48% protein, 21% lipids, 7% glycogen, 1% organic acids, and 1% nucleic acids. Approximately 70% of the lipids are fatty acids while 30% are phospholipids.

Cultured since the 1930s, microworms are suitable for some larval shrimps, aquarium fishes and carp species such as the bighead carp, marine fish larvae and Asian catfish larvae.

Microworm culture
Microworms are easy to culture. They can be cultured in a shallow, flat, watertight container using a moist paste of powdered oats and saline water at a 4:10 ratio. The mixture should have a very thick paste-like consistency. Five grams of baker's yeast is dissolved in 65 ml of saline water and five ml of the yeast solution is added to the culture media every 7 days.

The culture media is kept moist by adding 5 ml sterilized saline water daily. The containers are incubated in open shelves at 20°C for 10-14 days and covered with gauze to keep insects away.

Microworms can withstand temperatures below 32°F but can reproduce more under higher temperatures; however, cultures last longer at lower temperatures. The microworms feed on the yeast and bacteria produced from the oatmeal. After 3 to 7 days, the surface of the media glisten with the movement of the microworms, and they start climbing up the sides of the container.

Harvesting the microworms
The microworms are harvested after the incubation period (10-14 days). Into each container is added 4 liters of pre-aerated chlorinated seawater and strained twice using two kinds of sieves (300 and 150µm). The sieved mixture is allowed to settle for three hours after which three-fourths of the water is siphoned out.

The mixture is centrifuged at 5000 rpm for five minutes to concentrate the nematodes. After discarding the liquid on the surface, 50% sugar solution is added to the precipitate and centrifuged again to separate the nematodes from the debris. The nematodes that float are scraped off and rinsed several times with chlorinated seawater. The collected nematodes are suspended in water from which samples are taken. The clean nematodes are then fed to the grouper fry.

A more cost-effective way of harvesting the microworms is by simply scraping them from the sides and top of the container. A paint-stirring stick laid on the media provides additional surface from which to harvest. The 8" x 12" culture provides a harvest of approximately 1 to 1-1/2 teaspoons of microworms daily for three weeks or more.

Maintaining the culture
The surface of the culture should be stirred every week to maintain production. As the yeast utilizes the oatmeal, the mixture becomes thin and soupy, although the production of the worms remains the same. A piece of sponge can be placed on the media to soak up the excess moisture. Eventually, as the oatmeal is exhausted, reducing the nutrient supply for the yeast, the harvest of microworms diminishes and a new culture should be started.

Feeding the grouper fry
The grouper larvae could be fed with microworms as early as three days after hatching. Optimum feeding density is 75 nematodes for every milliliter. Scientists say that nutritionally-enriched nematodes did not significantly improve growth and survival of the larvae.

This means that local fish breeders can culture microworms at home instead of buying expensive fish feed or supplements and be sure that their grouper fry are getting the nutrients they need.

Indeed, fish breeders should try microworms as a better alternative for grouper fry. It is inexpensive, readily available and easy to raise and most importantly new fry and small fishes love them.

Source: Free-living nematode (Panagrellus redivivus) as alternative live feed for grouper (Epinephelus coioides Hamilton) larvae by Ofelia Reyes, Marietta Duray, Corazon Santiago, and Manuel Ricci of Southeast Asian Fisheries Development Center (SEAFDEC), SEAFDEC-AQD and Biotechnologie, B.T., Pantalla di Todi, Italy; Microworm Culture for Aquarium Fish Producers by R.W. Rottmann. This document is Fact Sheet FA-9, one of a series of the Department of Fisheries and Aquaculture, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. October, 1988. Please visit the FAIRS Web site at http://hammock.ifas.ufl.edu.