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Manual on the Production and Use of Live Food for Aquaculture - Phần 10

Tham khảo tài liệu 'manual on the production and use of live food for aquaculture - phần 10', nông - lâm - ngư, ngư nghiệp phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 6.1. Daphnia and Moina 6.1.1. Biology and life cycle of Daphnia 6.1.2. Nutritional value of Daphnia 6.1.3. Feeding and nutrition of Daphnia 6.1.4. Mass culture of Daphnia 6.1.5. Production and use of resting eggs 6.1.6. Use of Moina 6.1.1. Biology and life cycle of Daphnia Daphnia is a frequently used food source in the freshwater larviculture i.e. for different carp species and in the ornamental fish industry i.e. guppies sword tails black mollies and plattys etc. Daphnia belongs to the suborder Cladocera which are small crustaceans that are almost exclusively living in freshwater. The carapace encloses the whole trunk except the head and the apical spine when present . The head projects ventrally and somewhat posteriorly in a beak-like snout. The trunk appendages five or six pairs are flattened leaf-like structures that serve for suspension feeding filter feeders and for locomotion. The anterior part of the trunk the postabdomen is turned ventrally and forward and bears special claws and spines to clean the carapace Fig. 6.1. . Species of the genus Daphnia are found from the tropics to the arctic in habitats varying in size from small ponds to large freshwater lakes. At present 50 species of Daphnia are reported worldwide of which only six of them normally occur in tropical lowlands. The adult size is subjected to large variations when food is abundant growth continues throughout life and large adults may have a carapace length twice that of newly-mature individuals. Apart from differences in size the relative size of the head may change progressively from a round to helmet-like shape between spring and midsummer. From midsummer to fall the head changes back to the normal round shape. These different forms are called cyclomorphs and may be induced like in rotifers by internal factors or may be the result from an interaction between genetic and environmental conditions. Normally there are 4 to 6 Instar stages Daphnia growing from nauplius to maturation through a .