52 MARCH 2014 • WORLD AQUACULTURE • WWW.WAS.ORG Historically, marinederived nutrients in river systems of the Pacific Northwest were abundant from great numbers of salmon returning to their natal streams. At the turn of the twentieth century the biomass of salmon returning to Washington, Oregon, Idaho and California was 160-226 million kg (Gresh et al. 2000, Kohler et al. 2008). Now, the biomass of fish returning is 11.813.7 million kg. Therefore, just 6-7 percent of marine-derived nutrients that were previously deposited are now delivered to riverine ecosystems. As early as the 1950s, researchers realized there was a deficit of essential nutrients and they started work on nutrient enhancement of river systems (Stockner 2003). Streams were enriched with nutrients in the form of raw salmon carcasses, processed carcass analogs and commercially produced organic or inorganic fertilizers (Larkin and Slaney 1997, Bilby et al. 1998, Cederholm et al. 1999, Stockner 2003). Scheuerell et al. (2005) reiterate the need for marine-derived nutrients and energy to maintain salmonid stocks. One overlooked aspect is the presence of salmon eggs (Fig. 1) as a nutrient source in streams with carcasses (Jauqet et al. 2003). Stream salmonids are sight feeders (Higgs et al. 1995) that will consume, sometimes heavily, salmon and steelhead eggs (Shapovalov and Taft 1954, Johnson and Ringler 1979, Johnson 1981, Pauley et al. 1986, Simpson et al. 2009). However, the amount of eggs currently consumed by stream fish may be limited because of reduced availability. Salmon eggs, as a food source, can provide high-quality lipids (Sargent 1995) and other nutrients that can increase the condition of juvenile salmonids and possibly enhance winter survival (Johnson and Ringler 1979). The Use of Egg Analogs to Increase Natural Production of Steelhead Trout Oncorhynchus mykiss James M. Barron, Ron Twibell, Heidi Hill, Michael Newsom and Ann Gannam In considering every aspect of stream enrichment, the use of egg analogs should be tested to evaluate their potential to add to the nutrient base for stream salmonids. The purpose of this study was to evaluate potential egg analogs for their acceptance and suitability when offered to juvenile steelhead O. mykiss. A short-term feeding behavior trial (Stradmeyer et al. 1988) was conducted to evaluate the use of egg analogs and their acceptance by juvenile steelhead. A longer-term trial compared the suitability of extruded feeds with steelhead eggs. Feeds included a commercial salmon diet, an experimental diet, and the experimental diet dyed red to mimic steelhead eggs. Feeds were produced at U. S. Fish and Wildlife Service’s Abernathy Fish Technology Center in Longview, WA. Behavioral Study Behavioral trials were conducted in two identical 87-L observation tanks. Each tank was fitted with a viewing window and a PlexiglassTM baffle was used to create a chamber in the front of the tank with directional water flow that decreased in velocity from left to right. Groundwater at 15 C flowed into the chamber at 10.8 L/ min through a spray bar oriented at the left wall of the chamber to create a diffuse flow. The chamber bottom was lined with a 2.5-cm deep layer of pebbles averaging 17 mm in diameter. Each chamber was equipped with a 20-L underwater feeder plumbed to introduce feed particles near the substrate by flushing them into the chamber parallel to the direction of water flow to simulate a food item rolling downstream over the substrate. At the start of a trial, a randomly selected hatchery-reared juvenile (25 g) steelhead trout (Fig. 2) was added to the chamber of TOP, FIGURE 1. Steelhead eggs used in the feeding study and behavior trial. (Photo: James Barron, USFWS) BOTTOM, FIGURE 2. Juvenile steelhead trout at Abernathy Fish Technology Center. (Photo: James Barron, USFWS)
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