Chapter 7: Extensive Pond Production: Nursery Pond Preparation
Earthen ponds are used in the production of most warmwater fishes and several coolwater fishes cultured for food, bait or sport. Ponds are more appropriate than raceways for these species as ponds are more similar to natural habits of the fish, are a source of natural food, have lower construction costs and water requirements, allow simpler husbandry technology, and generally have lower production costs. Disadvantages include lack of direct control over both the fish and the environment and difficulty in monitoring the interactions of the fish with their environment. Ponds may be used as a natural spawning setting for species that will spawn in static water conditions. Ponds can be used for egg incubation, as well as larval and juvenile production. Larvae for stocking ponds can be obtained from induced or natural spawning in the hatchery, or from outdoor spawning ponds. The first 30 to 45 days in the life of the larvae are critical and is a point where significant mortality might be anticipated. During this period the fish make the transition from its larval food habits, feeding on zooplankton, to more adult food habits. Fish during this period can be managed in the hatchery, a combination of hatchery and pond production or ponds alone.
Ponds, if properly prepared can provide a very suitable culture environment for the first 30 to 45 days after the larvae have functional mouthparts and a complete digestive tract. Larval fish are zooplankton feeders, and ponds can provide rotifers, cladocerans and other suitable food items. However, there are limits in the quantities of zooplankton that can be produced and within 30 to 45 days post-stocking. The larval fish have grown, changed food preferences, and are consuming appropriate live food items faster than they can be replaced. Fish yields from such nursery ponds are often limited due to the amount of zooplankton that can be provided and are often less than 250 kg of fish/ha. The fish have developed from the delicate larvae at stocking to a much hardier juvenile fish that can be harvested safely from a pond. At that point the fish should be harvested and restocked at lower densities. This first pond culture period is called the primary nursery period. This first culture period is adequate to produce small fingerlings (26 to 60 mm) of many species suitable for distribution. However, larger size fingerlings are often needed and a second culture phase is needed (secondary nursery pond period).