Cladocerans as Fish food organisms

 Cladocerans

Cladocera or Cladocerans are small crustaceans commonly called water fleas, They are part of the Class Branchiopoda. They have soft body and are small in size therefore they form an important part in fish culture specially seed rearing process. A brief of Cladocerans is as follows

3.1.Cladocerans classification

   Kingdom - Animalia
     Phylum - Arthropoda
       Sub-phylum - Crustacea
         Class - Branchiopoda
           Sub-class - Phyllopoda
             Order – Cladocera

 3.2. Biology and nutritional value of cladocerans

In contrast to the prosperity of cladocerans in freshwater systems, with more than 600 recorded species, marine cladocerans show a very low diversity, with only eight truly marine species. These 8 species can be divided in two distinct groups, the Podonidae (represented by the genera Evadne, Pleopis, Podon and Pseudevadne), and the Sididae with only one species, Penilia avirostris).

 

3.2.1. Daphnia

The most commonly known genus is Daphnia (freshwater fleas), which is the most researched in this group and Moina. Cladocerans are free-swimming organisms, and most orientate themselves with dorsal side up. The head is typically separated from the body by a deep indentation, but also may not be separated. It projects forward as a beak or rostrum. On the forehead is an unpaired compound eye, a result of two fused eyes, and, in most species, a simple naupliar eye.

3.2.1.1. Daphnia classification

    Kingdom: Animalia
      Phylum: Arthropoda
        Sub-phylum: Crustacea
          Class: Branchiopoda
            Order: Cladocera
              Family: Daphniidae
                Genus: Daphnia

 

3.2.1.2. Nutritional value of Daphnia

The nutritional value of Daphnia depends strongly on the chemical composition of their food source. However, since Daphnia is a freshwater species, it is not a suitable prey organism for marine organisms, because of its low content of essential fatty acids and in particular (n-3) HUFA. Furthermore, Daphnia contains a broad spectrum of digestive enzymes such as proteinases, peptidases, amylases, lipases and even cellulase that can serve as exoenzymes in the gut of the fish larvae.

 

3.2.1.3. Nutritional value of Moina

The nutritional content of Moina varies considerably depending on their age and the type of food they are receiving. Although variable, the protein content of Moina usually averages 50% of the dry weight. Adults normally have a higher fat content than juveniles. The total amount of fat per dry weight is 20-27% for adult females and 4-6% for juveniles.

 

3.2.1.4. Biology and life cycle of Daphnia

Daphnia is a frequently used food source in the freshwater larviculture (i.e. for different fish species). Daphnia are small crustaceans that are almost exclusively living in freshwater. 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. 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. 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. Normally there are 4 to 6 Instar stages; Daphnia growing from nauplius to maturation through a series of 4-5 molts, with the period depending primarily on temperature (11 days at 10°C to 2 days at 25°C) and the availability of food. Daphnia species reproduce either by cyclical or obligate parthenogenesis and populations are almost exclusively female. Eggs are produced in clutches with parthenogenetic eggs produced ameiotically and result in females, but in some cases males can appear. Factors, such as change in water temperature or food depreviation as a result of population increase, may induce the production of males. The fertilized eggs are large, and only two are produced in a single clutch (one from each ovary), and are thick-shelled: these resting or dormant eggs being enclosed by several protective membranes, the ephippium.

Life cycle of Daphnia

3.2.2. Moina

Various species includes Moina affinis, M. australiensis, M. belli, M. brachiata, M. brachycephala, M. flexuosa, M. hartwigi, M. hutchinsoni, M. macrocopa, M. micrura, M. minuta, M. mongolica, M. rectirostris, M. reticulata, M. salina and M. tenuicornis. Adult Moina have an average size (700-1,000 µm) and are approximately the same size or only slightly larger than adult rotifers and smaller than newly-hatched brine shrimp. Moina are ideally suited for feeding freshwater fish fry as they have a longer life span. Moina micrura grown in ponds, fertilized with mostly chicken manure or, less frequently, with pig manure, are used as the sole food for fry of many ornamental tropical fish species, with a 95-99% survival rate.

 

3.2.2.1. Moina classification

    Kingdom: Animalia
      Phylum: Arthropoda
        Sub-phylum: Crustacea
          Class: Branchiopoda
            Order: Cladocera
              Family: Moinidae
                Genus: Moina

 

3.2.2.2. Life Cycles of Moina

The reproductive cycle of Moina has both a sexual and asexual phase. Normally, the population consists of all females that are reproducing asexually. Under optimum conditions, Moina reproduce at only 4-7 days of age, with a brood size of 4-22 per female. Broods are produced every 1.5-2.0 days, with most females producing 2-6 broods during their lifetime. Under adverse environmental conditions, males are produced and sexual reproduction occurs resulting in resting eggs (ephippia). The stimuli for the switch from asexual to sexual reproduction in populations of Moina is an abrupt reduction in the food supply, resulting in an increase in resting egg production. However, it is advantageous to keep the population well fed and in the asexual mode of reproduction, since fewer progeny are produced with resting eggs.

 

3.2.2.2.1. Production and use of resting eggs

Resting eggs are interesting material for storage, shipment and starting of new Daphnia cultures. The production of resting eggs can be initiated by exposing a part of the Daphnia culture to a combination of stressful conditions, such as low food availability, crowding of the animals, lower temperatures and short photoperiods. These conditions are generally obtained with aging populations at the end of the season. Collection of the ephippia from the wild can be carried out by taking sediment samples, rinsing them through a 200 μm sieve and isolating the ephippia under a binocular microscope. Normally, these embryos remain in dormancy and require a diapause inhibition to terminate this status, so that they can hatch when conditions are optimal. Possible diapause termination techniques are exposing the ephippia to low temperatures, darkness, oxygen and high carbon dioxide concentrations for a minimal period of several weeks (Davison, 1969). There is still no standard hatching procedure for Daphnia. Generally the hatching process is stimulated by exposing the ephippia to higher temperatures (17-24°C), bright white light, longer photoperiods and high levels of dissolved oxygen. It is important, however, that these shocks are given while the resting eggs are still in the ephippium. After the shock the eggs may be removed from the ephippium. The hatching will then take place after 1-14 days.        

                                                                         Stock culture

Collect Moina/Daphnia from stagnant water bodies like ponds and tanks with

 the help of a scoop net having 100-200 µ mesh.

 Place the content in a plastic bucket.

 Dilute the sample by adding clear water and examine under a microscope to pick up Moina/Daphnia with help of a dropper. 

Inoculate Moina/Daphnia @ 1-2 nos./ 10 ml of filtered water in a 20 ml glass tube.

Feed Moina/Daphnia with yeast or groundnut oil cake @200 ppm.  

After 3-4 days, transfer the test tube cultures into 1 liter glass jar or beaker and feed with yeast. 

After 5-6 days, use this cultures

for further inoculation in mass culture tanks.

 Steps of c mass culture

   For mass culture, 500-1000 litre capacity cement cistern or plastic pools.

 Wash the culture tank thoroughly with clean ground water or 1%‎ KMnO₄.

         Fertilize the tank with slurry @ 3-4 ml/liter for 3-4 days regularly.

On 3^rd or 4^th day of fertilization, inoculate the tank with Moina/Daphnia @

   40-50 individual/litre.

 In about 6-7 days, Moina/Daphnia multiplies and reaches to a peak density, ranging from 10,000-25,000 individual/litre.

      Harvest the Moina/Daphnia in morning or late evening.