The Nutrition Physiology Research Team has developed a partially denatured egg yolk suspension by mixing the yolk with a formalin solution and rapidly beating the resultant partially denatured protein into particles of approximately 100 millimicron diameter which had many desirable characteristics for initial feeding of carp fry. The process produces particles which are readily accepted, are semi-moist, and contain high amounts of protein and fat. The amino acid pattern should support growth of young carp. These were tested with young guppies and found good growth for several weeks until the young fish could take larger particles of more traditional food. The process will destroy the vitamin C present in the egg yolk, and consequently either stable C2 must be added to the solution, or another technique adopted to prepare the particles.
The egg microencapsulation technique described by Dr Chow in Fish Feed Technology1 was reviewed with the team. This hotwater whole egg suspension preparation has several advantages over the formalin technique. The balance of nutrients should support growth of the small fish larvae since adequate digestible protein and fat for energy are available in this preparation. Plans were made to test this larval feed on initial feeding common carp, Cyprinus carpio, in Zug jars in the water recycle together with several other types of larval feed. Acceptance and amount consumed will be tested first, then a growth and survival study will be made when the majority of the larvae eat the feed.
A sample of HP 815 made by predigesting fish wastes and then combining this polypeptide source with other communities plus vitamin and mineral mixes to form a slurry which is then flash-dried on a double drum dryer in less than 20 seconds to form a thin film which can be pulverized and screened to various particle sizes, was demonstrated. The equipment to prepare this type of larval feed is not expensive and within the capabilities of the staff at Haki. Only a double-drum dryer and proper screens are necessary additions to the equipment on hand. The advantages of this type of preparation are its versatility for utilization of partially digested (pepsin treated) proteins which can be adjusted to present a desired amino acid profile, and the flexibility with which one may prepare diet particles with good water stability and which upon addition to water swell about 20 percent in diameter to present a soft flesh-like gel to the fish. Particles can be manufactured in sizes ranging from 10 to 200 microns and with positive control of the nutrients combined within the formulation. This allows design of larval test feeds in various sizes for various species and ages of fish, and allows the nutritionist to design nutrient profile treatments into the larval feeding trials. Flake feeds can also be made for larger larvae or for fry feeding until such time as more traditional feed preparations can be used. The particles are remarkably stable and retain nutrients well during the convenient dry storage of packaged sealed samples of the larval feed. Two packages of HP 815 of 100 g each were left with the staff for testing. Arrangements have been made to supply more samples in various sizes for testing on common and Asiatic carps, pike-perch, and sheatfish.
A standard protocol for the testing of various larval feed preparations was developed and presented to the staff. The standard protocol used for marine fish larval feed testing, and for preliminary freshwater fish larvae, was adapted for use in the Zug glasses used in the larval rearing experiments in the recycle system at Haki. Triplicate groups of larvae will be held 500 per lot in Zug glasses. As soon as the swim-up period occurs and the yolk-sac has been absorbed, each lot will be fed 100 mg of wetted or soft microencapsulated particles during the daylight hours at five scheduled feeding periods. After three days on test, 50–100 larvae from each lot will be removed from the jar 15 min after feed was offered for the first time on day 3. These individual larvae will be examined under a dissecting scope for the presence of feed particles in the stomach or in the first half of the gut tube. The number of fish with particles in the digestive tract will be recorded and the number of particles present in the first third of the gut tube will be recorded. An Index of Acceptance and Wolf's Index of Fullness will be calculated1. Larval feed testing is planned for several periods during the spawning sequences managed at Haki in the water recycle system. This will involve pike in March, pike-perch in April, carp in May, herbivorous carps in May and June, and sheatfish in June. Results will be compared with the degree of acceptance measured for the HP preparations in marine fish larvae, and in brackishwater fish testing systems. One preliminary test with HP 815 was conducted in October with carp which had been induced to spawn in the recycle system. Results were very encouraging - by day 3 of feeding all carp had particles in the stomach, and discernible digestion and elimination was observed in each larvae examined. These tests will be repeated in 1982 and continued through 1985 in order to develop an acceptable larval fish feed.
