Despite many years of research on larval fish diets, a "bottle neck" for aquaculture of many fish species is the lack of a suitable larval diet package that supports larval growth and survival comparable to live feeds. We propose to utilize "state-of-the-art" encapsulation technology to encapsulate complex mixture of nutrients needed in a suitable larval diet. We propose:
To develop an encapsulated diet for first feeding of yellow perch larvae;
To evaluate the effect of feed attractants (amino acids) incorporated in the diet on ingestion of the encapsulated diet;
To determine the basic nutritional requirements of yellow perch larvae;
To evaluate the use of encapsulated beads as carriers for different substances such as antibiotics and hormones to the larval body.

The results of this work will allow the use of 'off-the-shelf' diets as the first food for yellow perch larvae. This will decrease the variability in growth and survival of the larvae that are usually reared on zooplankters. The production of microencapsulated diets is an appealing approach to deliver nutrients, vaccines, enzymes, hormones and other substances into small fish larvae. The microencapsules will allow rearing several batches of perch per year. The know-how acquired in the successful development of microencapsulated nutrient formulations applicable to feeding yellow perch larvae will be applicable to a range of other fresh and marine fish larvae as well as other biological applications.

The first task will be to develop a capsule with a shell that will retain aqueous solutions of soluble fish proteins during a prolonged period of immersion in water. Criteria such as: size, shape, buoyancy, shell thickness and amount of water-soluble nutrients in the liquid core will be the primary parameters considered. The second stage will be to determine the influence of different fish attractants on the ingestion of microcapsules by larvae. Different L-amino acids and higher molecular weight substances will be tested to improve the larval ingestion rates. Leaching of the free amino acid from the beads will also be determined. The second year will focus on the nutritional value of the microcapsules. Results of current nutrition experiments with yellow perch larvae being conducted at OSU and Purdue University, IL will provide the basis for planning this work. We will evaluate the use of fish and krill hydrolysate as the protein source for the yellow perch larvae, as well as the lipid source in terms of n-3 PUFA. Finally, this work will test the use of encapsulated particles as carriers for digestive hormones to enhance the digestive system activity.

Live zooplankters currently are used for the intensive culture of fish larvae and can be continued past metamorphosis when fish are weaned onto dry formulated diets. Formulated microdiets represent an alternative approach that, if successful, could provide numerous advantages. However, existing microdiets have not matched the growth and survival demonstrated by larvae fed rotifers and newly hatched Artemia nauplii. It has become increasingly clear that the dietary needs, both quantitatively and qualitatively, of growing larvae are distinctly different from those of adult fish. During larval "metamorphosis", the digestive tract is still developing and not totally functional. This leads to insufficient digestion and assimilation of packaged microdiets. Microcapsules offer a means of packaging microdiets and have been explored for a number of years as a means of delivering intact microdiets to fish and fish larvae. The results have been mixed due primarily to the complexity of designing a capsule shell suitable for this application. In addition to retaining all nutrients needed to support growth and development of fish larvae, microcapsules loaded with microdiets must satisfy a number of physical and chemical requirements. The purpose of this presentation was to briefly summarize the current status of microencapsulated microdiets for fish larvae and discuss the various properties that microcapsules designed to deliver microdiets to fish larvae must have. Particular attention was focused on the need to develop a microcapsule shell that retains water-soluble components of a diet upon immersion in water for a finite time while rapidly releasing all microdiet components when a capsule is ingested by a fish larvae. This can occur if the capsule shell biodegrades to some degree in the larval gut due to enzymatic attack. Results of preliminary feeding studies obtained to date with microcapsules supplied by Thies Technology and the Instituto de Ciencias Marinas de Andalucia (Spain) was used to illustrate the various problems of developing a suitable microcapsule.

We determined the effect of krill hydrolysate as a feed attractant in three freshwater fish species: yellow perch Perca flavescens, walleye Stizostedion vitreum, and lake whitefish Coregonus clupeaformis. Growth trials were conducted using a commercial trout starter diet (control) and the diet that was coated with liquid hydrolysate. The krill hydrolysate coated diet increased growth of yellow perch juveniles by 31% compared to control diet (average final wet weight, 734 ± 33 mg and 559 ± 82 mg, respectively). Moreover, wet gains were not significantly different than for fish fed exclusively live Artemia nauplii. Similar results were obtained with walleye juveniles fed either a trout starter diet or 5% krill hydrolysate coated diet (8.9 ± 0.25 g and 11.6 ± 5.1 g wet weight, respectively). The food conversion ratio (FCR) was lower in fish fed the control diet, although not significantly different (2.95 ± 0.18 and 3.69 ± 0.39, for control and coated diet, respectively). The effect of krill hydrolysate on dry diet ingestion rates of lake whitefish and yellow perch larvae was also determined using radioactive (¹⁴C) labelling. A commercial starter diet was coated with krill hydrolysate or the soluble fraction of krill hydrolysate was added to the experimental tank water. In both species, coating the diet with 5% krill hydrolysate resulted in significantly higher ingestion rates. Supplementation of krill hydrolysate soluble fraction to the tank water resulted in 200% increase in ingestion rate in comparison to control (uncoated starter diet), although it was significantly different from krill coated diet and live Artemia nauplii ingestion rates.

In spring 2000, yellow perch larvae were raised on Ohio State University's Columbus campus, and in some batches more than 70 percent successfully filled their swim bladders and showed excellent growth. Several thousand of the juvenile fish were then transferred to an artificial diet and continued to grow. Coating the dry trout diets with krill hydrolysate made the diet more attractive to yellow perch. These advancements in larval rearing of yellow perch coupled with our success in inducing out-of-season spawning will lead towards intensive production of yellow perch and availability of feed-trained fingerlings for commercial aquaculture.

Preliminary studies with microencapsulated diets provided by Theis Technology (St. Louis, MO) resulted in low diet acceptance and negligible growth of yellow perch. Further studies are required with significant changes in microencapsulation technology.