Effect of Diet Processing Method and Ingredient Substitution on Feed Characteristics and Survival of Larval Walleye, Sander vitreus

Two methods were developed for the production of larval fish diets. The first method, microextrusion marumerization (MEM), has been tested in laboratory feeding trials for many years and produces particles that are palatable and water stable. The second method, particle-assisted rotational agglomeration (PARA), produced diets that have lower density than diets produced by MEM. Each method was used to produce diets in the 250to 400and 400to 700-mm range and compared with a reference diet (Fry Feed Kyowa* [FFK]) for feeding larval walleye in two experiments. The effect of substituting 4% of the fish meal with freeze-dried artemia fines was also investigated. In the first experiment, 30-d survival was greater (P , 0.05) for fish fed a diet produced by PARA without Artemia (49.1.0%) than for fish fed the same diet produced by MEM (27.6%). The addition of Artemia to a diet produced by MEM did not increase survival of larval walleye. Fish fed the reference diet had 24.4% survival. In the second experiment, there was an effect of both processing method and Artemia supplementation, and an interaction of these effects, on survival. Fish fed a diet produced by PARA without Artemia supplementation had 48.4% survival, and fish fed the same diet produced by MEM had only 19.6% survival. Inclusion of 4% freeze-dried Artemia improved (P , 0.04) survival of fish fed MEM particles but not those fed PARA particles. Fish fed FFK had greater weight gain than fish fed other diets in both experiments. Data indicate that the PARA method of diet processing produces smaller, lower density particles than the MEM process and that diets produced by the PARA process support higher survival of larval walleye with low capital and operating costs. Production of walleye fingerlings and other small-egged species has traditionally relied upon pond rearing or feeding live Artemia during the first 30 d of culture (Colesante et al. 1986). The development of specialized larval diets (e.g., BioKyowa) and modified rearing techniques (Loadman et al. 1989; Barrows et al. 1993) now allow for intensive larval walleye culture using only formulated diets. In the late 1980s, survival greater than 10% was considered good for larval walleye fed formulated diets (Barrows et al. 1988; Loadman et al. 1989). With the rearing techniques and diets now available, survival rates as high as 50% are observed in a production hatchery (A.Moore, IowaDepartment of Natural Resources, Moravia, IA, USA, personal communication), although tank production of larval walleye is very limited. Walleye production is primarily for sport-fishing purposes, with only a few attempts being made at food fish production. Modern commercial larval diets differ from traditional steam-pelleted crumbles in both composition and method of manufacture, and they possessgreaterwater stability andpalatability than traditional fry diets. However, the precise method of manufacture and ingredient composition of commercial larval diets remains proprietary. The U.S. Fish and Wildlife Service had been engaged in development of open-formula larval diets for use in fisheries restoration programs (Barrows 1990, 1991, 1994, 1995). Numerous methods of particle formation were tested during 1 Corresponding author. * Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. JOURNAL OF THE WORLD AQUACULTURE SOCIETY Vol. 37, No. 2