Cooperative Fish and Wildlife Research Units Program: Montana Fishery
Education, Research and Technical Assistance for Managing Our Natural Resources

Summary Conservation propagation facilities in the Upper Basin are currently experiencing variable survival of first feeding larval Pallid Sturgeon. This type of hatchery-induced “selection” can ultimately have unintended, negative consequences on genetic representation of Pallid Sturgeon returned to the Missouri and Yellowstone Rivers, and managers are now investigating potential sources of mortality in the hatchery. Larval mortality is high at 19-21 days (at 16-18°C) and occurs as a result of starvation. This study seeks to determine if survival and condition of first feeding larval Pallid Sturgeon and successful weaning to a formulated diet can be enhanced by a diet more similar to dietary options in the wild. The results of this study can be used to develop a feeding regimen to enhance survival and condition of larval Pallid Sturgeon in conservation propagation facilities. Problem Statement and Background Conservation propagation is defined as the production of individuals for reintroduction in the wild, and is a critical component of recovery plans for aquatic species at risk of extinction or population loss (Paragamian and Beamesderfer 2004; Caroffino et al. 2008; George et al. 2009; Lorenzen et al. 2010). Conservation propagation has been used to successfully augment populations of multiple imperiled fishes, like Chinook Salmon Oncorhynchus tshawytscha (Fast et al. 2015), and continues at present to be the main source of production of larval Pallid Sturgeon Scaphirhynchus albus in the Upper Missouri River Basin (Steffensen et al. 2010). USFWS conservation propagation hatcheries are currently experiencing variable survival of post-hatch larval Pallid Sturgeon following initiation to exogenous feeding, which directly affects the genetic lots that are returned to the upper Missouri River and potentially artificially selects the genetic composition of the Pallid Sturgeon population in the Upper Missouri River Basin. There is indication that the observed variability in larval survival at conservation propagation hatcheries is a result of poor response to feed offered to larvae. First feeding larval Pallid Sturgeon in a hatchery setting are introduced to a formulated diet (Otohime) at 3-5 d post-hatch, depending on water temperatures (Webb et al. 2006). However, recent research conducted on multiple species of fish, including several sturgeon species, suggests that first feeding larvae are not well-suited for a formulated diet (Parauka et al. 1991; Bardi et al. 1998; Mohler et al. 2000). First feeding larvae may not be adequately stimulated by the texture or appearance of formulated feed (Person Le Ruyet et al. 1993). However, because visual capabilities are likely not fully functioning at this early stage, chemical attractiveness of food is highly important (Iwai 1980; Kolkovski et al. 2000). There is evidence that formulated dry diets do not have the chemical attractiveness required to cue the taste and olfaction senses or initiate the preliminary stages of digestive processes that first feeding larvae utilize when feeding (Buddington 1985; Kolkovski et al. 1997a). There is also evidence that first feeding larvae are unable to properly digest formulated diets because of the digestive enzymes present at this stage. Lipase and amylase, the digestive enzymes present at high levels during the time of first feeding, process food sources rich in carbohydrates and glycogen, like the early life-stage zooplankton found in a natural aquatic setting (Buddington and Christofferson 1985; Ricardi 2000; Ware et al. 2006). As larvae transition through the period of first feeding, the complement of digestive enzymes shifts towards greater levels of pepsin, which processes food sources rich in proteins (Ware et al. 2006). Formulated diets, like those currently fed to first feeding sturgeon, are high in protein, and, though digestible at a later period, may be too difficult for early sturgeon larvae to digest and assimilate (Ware et al. 2006). This can result in reduced body weight and larval mortality. Formulated diets have also been shown to result in high levels of larval cannibalism in Beluga Sturgeon (Huso huso; Agh et al. 2012). Enhancement of the traditional feeding regimen offered to first feeding larvae has been demonstrated to significantly improve survival and condition in multiple species of fish. In one study of Yellow Perch Perca flavescens and Lake Whitefish Coregonus clupeaformis larvae, chemical enhancement of a formulated dry diet was made through top-coating with liquid krill hydrosolate. Food ingestion and larval growth were significantly greater in larvae that received the krill oil-coated dry diet than those that received the regular formulated diet (Kolkovski et al. 2000). Recent research on sturgeon suggests that the addition of live feed (i.e., Artemia) significantly improves larval survival and condition (Ware et al. 2006; Agh et al. 2012). Additionally, Ware et al. (2006) found that a diet comprised of Artemia alone did not affect survival or condition differently than a diet comprised of both formulated diet and Artemia. This is important because it identifies a feeding regimen that improves survival and condition, is not as costly or time-consuming as a diet comprised solely of live feed, and potentially improves weaning success by enabling larvae to imprint on the dry diet. Dietary requirements of larval fishes are likely species-specific (Hamre et al. 2013). Previous research conducted in 2007 and 2008 on feeding regimens for first feeding Pallid Sturgeon larvae found similar survival (73%-92%) among larvae fed a combination of a formulated diet (Otohime) and live Artemia and other diets containing variations of either solely Otohime or Otohime and additional dietary supplements (Kappenman et al. 2011). However, in this study Artemia were only fed to larvae once per day, which is likely too infrequent to significantly impact larval survival compared to dry diets. Similar research on other sturgeon species presented live Artemia six times per day at regular intervals (Ware et al. 2006; Agh et al. 2012). Given the variability of survival of first feeding Pallid Sturgeon larvae at conservation hatcheries, additional research is necessary to reduce hatchery selection.