Ward's World Working with Guides

+ ward ' s science 5100 West Henrietta Road • PO Box 92912 • Rochester, New York 14692-9012 • p: 800 962-2660 • wardsci.com Care and Feeding Hydra are best kept in an aerated aquarium or tub. Keep the temperature relatively low (18 – 21°C), provide a steady source of food, and ensure the water supply is free of contaminating chemicals. Brown Hydra prefer colder temperatures and tend to be larger and healthier in the winter months. Note: Hydra cultures, under usual methods of cultivation, undergo a period of depression in which the animals refuse to feed, the tentacles fail to expand, disintegration sets in, and the colony dies out. Therefore, it is recommended that you cultivate more than one culture at a time. Use only pond water or a mixture of pond water and deionized water. If tap water is used, remove salts with a water conditioner; the conditioned water can be used immediately. If the water is filtered, it is not necessary to change the water; however, if it is not filtered, the water should be changed daily. Hydra may be fed the larvae of brine shrimp (larger hydra may also feed on Daphnia). Brine shrimp are easy to raise and maintain in the lab: Fill a brine shrimp hatchery with one liter of salt water and two level teaspoons of brine shrimp eggs. Aerate the hatchery and allow eggs to hatch; this will take approximately two days. Collect the larvae by stop-ping the aeration and placing a light at one end of the hatchery. The brine shrimp will be attracted to the light, separating from the eggs that failed to hatch. Remove the larvae with a pipet and place them in an aquarium net lined with a piece of cloth. Rinse the brine shrimp under treated tap water to remove the salt, then pour them into a container of treated tap water. Use the brine shrimp immediately, as they will die quickly in tap water. Feed the Hydra daily by scattering the brine shrimp over the colony with a pipet. Allow approximately half an hour to an hour for feeding, then pour off the water with the remaining brine shrimp. You may also pour the water directly into a bowl and swirl the water to collect the Hydra; the Hydra will be moved toward the center of the bowl. Return the Hydra to their original container or place them in a new container. Because green Hydra's symbiotic alga is photosynthetic, the green Hydra can be sustained for several weeks without food, provided there is adequate sunlight or wide-spectrum artificial light. Keep the temperature below 25°C (higher temperatures promote rapid growth of algae, which will choke out the Hydra). To keep green Hydra healthy however, they should be fed small crustaceans. Green and brown Hydra can be kept in a refrigerator in jars for two to three weeks without feeding or water changes. After a few days without feeding, the Hydra will begin to rise to the surface for easy collecting with a pipet. Culturing Hydra In a proper environment, Hydra will bud profusely and at times produce sexual individuals. Cultures that are fed and cleaned daily will produce spontaneous sexual differentiation. Note: Aeration will inhibit the development of sexual individuals; if you want to induce development of sexual stages, aeration should not be used. Temperature reduction will also usually bring about the production of sexual forms. The simplest method is to place the Hydra culture on the bottom shelf of a refrigerator and feed daily. © 2021 Ward' s Science. All rights reserved. Rev. 2021

• Cover