Selection for Surface Feeding in Farmed and Sea-Ranched Masu Salmon Juveniles

Abstract

The feeding behavior of Japanese masu salmon Oncorhynchus masou (also known as cherry salmon) 3–4 months old differed among fish from wild, farmed, and sea‐ranched parents. Between feeding intervals, wild‐derived fry groups stayed lower in their separate stream tanks than farmed or ranched fry. When slow‐sinking food was offered, the wild fry made foraging bouts from the bottom, whereas the domesticated (farmed and sea‐ranched) fry stayed close to the surface. Consequently, the domesticated fry finished their meal faster than the wild fish. Over time, all stocks moved up higher in the water column and fed faster, but a difference between wild and domesticated fish persisted. Levels of aggression were similar among the three stocks and observation periods. Sea‐ranched fish were intermediate between wild and farmed fish in most recorded behaviors. Staying close to the water surface obviously is a successful strategy under standard salmon husbandry conditions, but an innate tendency to seek the surface is probably maladaptive in the wild. New hatchery techniques that teach fish to avoid the surface or prevent selection for surface‐seeking behavior promise to bolster the survival of postrelease ranched salmon.

Vertical dynamics and reproductive behaviour of farmed and wild Atlantic cod Gadus morhua

“…Nevertheless, behavioural choice rather than physiological imperative is not only the most parsimonious explanation, but also the most plausible. Earlier studies have shown that surface feeding and high stocking densities create strong benefits for hatchery fish that adopt shallow positions (Reinhardt 2001, reviewed by Olla et al 1994. Adult farmed cod are kept in sea pens that are much deeper than hatchery tanks, yet they are still surface fed and limited to a very narrow depth range compared to their wild counterparts.…”

“…However, when species such as teleost fishes are domesticated or captive-reared for aquaculture or re-introduction programmes, they are usually kept in shallow tanks or sea pens. These conditions, in concert with high stocking densities, a general absence of predators, surface feeding and artificial selection regimes, are likely to result in rapid divergence in depth-related behaviour between farmed and wild fish (Reinhardt 2001). Indeed, farmed fish often maintain positions closer to the surface than their wild counterparts (Vincent 1960, Dickson & MacCrimmon 1982, often for substantial periods of time after release .…”

Selection and genetic drift in captive versus wild populations: an assessment of neutral and adaptive (MHC-linked) genetic variation in wild and hatchery brown trout (Salmo trutta) populations

“…The environmental conditions in captivity often differ drastically from natural surroundings and include altered diet, increased or reduced populations sizes, different pathogen stress and the release from ecological forces such as competition or predation. These changes manifest themselves in behavioural (Price 1999;Reinhardt 2001), morphological (O'Regan and Kitchener 2005;Stringwell et al 2014) and physiological changes (Quispe et al 2014;Roznere et al 2014).…”

Genetics of behavioural adaptation of livestock to farming conditions

“…Lahti et al (2001) found evidence of a genetic basis for aggressive behaviour in brown trout; they observed that searun populations were more aggressive than lake-run or nonmigratory populations. Conversely, Reinhardt (2001) did not find such a difference in Masu salmon. Divergent selection for plasma cortisol responsiveness to an acute confinement stress in trout showed that fish from the high line were more mobile in the presence of an intruder (Øverli et al, 2002) Genetics of behavioural adaptation in livestock than fish from the low line; this suggests a link between fear and an aggressive response.…”