Abstract
Hatchery‐reared fish show high mortalities after release to the wild environment. Explanations for this include potentially predetermined genetics, behavioral, and physiological acclimation to fish farm environments, and increased vulnerability to predation and parasitism in the wild. We studied vulnerability to Diplostomum spp. parasites (load of eye flukes in the lenses), immune defense (relative spleen size) and antipredator behaviors (approaches toward predator odor, freezing, and swimming activity) in hatchery‐reared juvenile Arctic charr (Salvelinus alpinus) using a nested mating design. Fish were exposed to eye‐fluke larvae via the incoming water at the hatchery. Fish size was positively associated with parasite load, but we did not find any relationship between relative spleen size and parasitism. The offspring of different females showed significant variation in their parasite load within sires, implying a dam effect in the vulnerability to parasites. However, the family background did not have any effect on spleen size. In the mean sire level over dams, the fish from the bolder (actively swimming) families in the predator trials suffered higher loads of eye flukes than those from more cautiously behaving families. Thus, the results indicate potentially maternally inherited differences in vulnerability to eye‐fluke parasites, and that the vulnerability to parasites and behavioral activity are positively associated with each other at the sire level. This could lead to artificial and unintentional selection for increased vulnerability to both parasitism and predation if these traits are favored in fish farm environments.
Highlights
Every year, billions of farm-raised fish are released into lakes, rivers, and seas to support, rehabilitate, and maintain natural populations (e.g., Brown & Day, 2002; McNeil, 1991; Neff, Garner, & Pitcher, 2011)
Fish farm conditions might favor and produce a ‘farm stock’ equipped with traits that are beneficial to the fish farm environment relatively quickly at the expense of natural antipredatory behavior or decreased vulnerability to parasitism, which may lead to poor survival in the wild
If certain inherited behavioral traits, like high swimming activity associated with increased feeding activity, are favored in the fish farm populations, it can reflect on other traits, like vulnerability to parasitism
Summary
Billions of farm-raised fish are released into lakes, rivers, and seas to support, rehabilitate, and maintain natural populations (e.g., Brown & Day, 2002; McNeil, 1991; Neff, Garner, & Pitcher, 2011). Natural selection acts to favor weaker antipredator behavior in habitats with lower predation risk (Chivers & Smith, 1998; Chivers, Wildy, Kiesecker, & Blaustein, 2001; Lima & Dill, 1990; Riechert & Hedrick, 1990) and this is, in general, bound to the co-evolutionary cycles between predator and prey (cf “Red Queen” hypothesis of Van Valen, 1973) Supporting this possibility, experimental studies have clearly demonstrated that predation can have an effect on various fitness- related traits (e.g., Grostal & Dicke, 1999; Hedrick & Kortet, 2006). D. spathaceum parasites cause impaired vision and even blindness for fish by forming cataracts (Kuukka-Anttila, Peuhkuri, Kolari, Paananen, & Kause, 2010) This has been suggested as a notable factor affecting survival of fish by increasing risk of predation and lowering feeding abilities depending on the environment (e.g., Gopko et al, 2017; Mikheev, Pasternak, Taskinen, & Valtonen, 2010; Seppälä, Karvonen, & Valtonen, 2004).
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