World Aquaculture September 2018

WWW.WA S.ORG • WORLD AQUACULTURE • SEP TEMBER 2018 59 ( C O N T I N U E D O N P A G E 6 0 ) Idaho and can climb vertically up waterfalls they encounter along the way using their oral discs. When they arrive at their spawning grounds, they take the time to carefully build a nest by moving stones with their mouth before spawning. If a lamprey makes it this far, it will die where its life began, depositing a dose of marine nutrients into the freshwater environment. It is no surprise given the impressive life of this iconic species that they are a critical part of the ecosystems they inhabit. They are also significant part of the culture of Native American tribes in the region, representing an important food source that is used in tribal feasts and celebrations. Warm Springs Tribal Council member Ron Suppah explains that “The Creator told the people that the eels would always return as long as the people took care of them, but if the people failed to care of them, they would disappear.” Therefore, growing conservation efforts are focusing on this species and aquaculture is one aspect that may be used to supplement declining populations (CRITFC 2011). Culture methods require further development before conservation aquaculture can be applied for this species. As with most anadromous species raised for conservation purposes, the freshwater phase is where the majority of time in captivity occurs. For Pacific lamprey most of their freshwater life occurs during the larval stage, which can take up to seven years to complete (Close et al . 2002). The unique biology of this species during the larval phase creates challenges that require development of unconventional culture techniques. To enhance our ability to culture Pacific lamprey, scientists at the U.S. Fish andWildlife Service’s Abernathy Fish Technology Center (Washington State, USA) have been investigating the effects of rearing temperature on larvae at 86 and 554 days post hatch (DPH). Water temperature is a key consideration when culturing fish because it affects metabolism, development, growth, survival, and fatty acid profile of fish (Andrews and Stickney 1972, Brett 1979, Piper et al . 1982, Blaxter 1992, Barron et al . 2012). A given species can tolerate a range of temperatures, but within that range there is an optimumwhere metabolism functions most efficiently (Piper et al . 1982). The optimum rearing temperature may also shift through the life history of the fish (Piper et al . 1982). Early Larval Trial (86 DPH) Four treatment temperatures were maintained over the course of a six-week trial during the summer. Groundwater was heated to achieve treatment temperatures, with ambient groundwater being the lowest temperature tested. Inline water heaters were used to warm the single-pass water, causing several complications that required resolution before experiments could begin. First, heaters created oscillations in water temperature as they switched on and off. An inline mixing cell was installed after each heater to smooth variation in temperature before water was passed to culture tanks (Fig. 1). In addition, once water was heated, excess gasses formed that were potentially harmful to fish and could accumulate in water lines, creating a potential airlock. Bleeder valves were installed on incoming water lines to allow free gasses to purge. Packed columns followed by small aerated head boxes were added to each culture tank to strip excess gases from the incoming water and reduce the concentration of dissolved gasses from groundwater to a safe level for fish (Fig. 2). Three replicate tanks were maintained at each treatment temperature level via incoming single-pass water. Treatments included average temperatures of 14.7, 17.3, 19.2 and 22.4 C. Rinsed and sifted sand was added to each tank as substrate for burrowing by lamprey. Fifty fish at 86 DPH and 3.7 mg average weight were stocked into each tank (Fig. 3A). Although lamprey are filter-feeders at this stage, they were fed twice per week with a slurry of yeast and larval fish diet while water flowwas shut off for five hours. The substrate was flushed with water every other week during the experiment to maintain water quality within the tank. Survival of the young larvae was high (>98 percent) at all treatment temperatures. Larvae grew quickly at all rearing temperatures tested, although final weight was reduced in fish reared at 22.4 C (Fig. 4). A lamprey-specific condition factor was calculated (Lampman et al. 2016) and fish had robust values regardless of rearing temperature. Total whole-body lipid was not affected by temperature and ranged from 1.9 to 2.2 percent among treatments. Fatty acids are an important part of cell membrane structure FIGURE 3. Early larval Pacific lamprey at the beginning of a temperature trial (left). Older larvae at the end of a temperature trial (right) (Photo: James Barron).