Mortality and fish welfare

Abstract

Mortality has received insufficient attention as a fish welfare topic. Here, we aim to prompt fish farming stakeholders to discuss fish mortalities in relation to welfare. Mortality in farmed fish populations is due to a variety of biotic and abiotic causes, although it is often difficult to differentiate between underlying and immediate causes of mortality. Most mortality appears to occur during episodes associated with disease outbreaks and critical periods (in development or production). Most causes of mortality can be assumed to be associated with suffering prior to death. As mortality rates in farmed fish populations are suspected to rank amongst the highest in commonly farmed vertebrate species, mortality should be a principal fish welfare issue. Long-term mortality rates can be used as a retrospective welfare performance indicator and short-term mortality rates as an operational welfare indicator. Scrutiny of mortality records and determining causes of death will enable action to be taken to avoid further preventable mortality. The welfare performance of fish farms should only be judged on levels of predictable and preventable mortality. Fish farmers will already be monitoring mortality due to commercial and legal requirements. As profitability in fish farming is directly linked to survival, confronting mortality should ultimately benefit both fish and farmers.

Spatio‐temporal variations in mortality during the seawater production phase of Atlantic salmon (Salmo salar) in Norway

“…Most often, death of the individual fish is the endpoint of a period of bad welfare due to stress, disease, injury or parasitic infestations. Thus, mortality in a population can be used as a crude, but measurable, indicator of fish welfare, where an increase in mortality is considered an indicator of welfare problems (Ashley, ; Ellis, Berrill, Lines, Turnbull, & Knowles, ). Monitoring and minimizing mortality must be a top priority in an ethical production of animals.…”

“…In order to increase their production, producers are implementing new technologies and changing production methods. Measures of mortality and comparison to baseline mortality can be used to evaluate the impact on fish welfare due to a population increase, as the long‐term mortality in individual farms can be used as a performance indicator (Ellis et al, ). Therefore, knowledge on what mortality can be expected under “normal” production will be a valuable tool to evaluate new technologies (Soares, Green, Turnbull, Crumlish, & Murray, ; Stien, Oppedal, & Kristiansen, ).…”

“…In order to increase their production, producers are implementing new technologies and changing production methods. Measures of mortality and comparison to baseline mortality can be used to evaluate the impact on fish welfare due to a population increase, as the long-term mortality in individual farms can be used as a performance indicator (Ellis et al, 2011).…”

Effects of density, PVC-tubes and feeding time on growth, stress and aggression in African catfish (Clarias gariepinus)

“…crowding, sudden temperature changes, sorting, handling, transport (Huntingford, Adams, Braithwaite, Kadri, Pottingers, Sandøe & Turnbull 2006;Ashley 2007;Boerrigter, Manuel, van den Bos, Roques, Spanings, Flik & van de Vis 2013;Boerrigter, de Van Vis, van den Bos, Abbink, Spanings, Zethof, Louzao Martinez, Van Andel, Lopez-Luna & Flik 2014; der Heul, van den Bos, Flik & van de Vis 2014) and pathogens (Bertotto, Poltronieri, Negrato, Richard, Pascoli, Simontacchi & Radaelli 2011). In fish, stressors may also lead to decreased welfare, health problems and mortality (Soares, Green, Turnbull, Crumlish & Murray 2011;Ellis, Berrill, Lines, Turnbull & Knowles 2012), when they overtax the adaptive capacity of the animal. Stress responses in fish comprise hormonal changes (Mazeaud, Mazeaud & Donaldson 1977;Wendelaar Bonga 1997), changes in metabolism (Mazeaud et al 1977;Wendelaar Bonga 1997), blood ions and haematology (Barton 2000) to adjust to the challenging situation.…”

Salmon welfare index model 2.0: an extended model for overall welfare assessment of caged Atlantic salmon, based on a review of selected welfare indicators and intended for fish health professionals

“…Removal of fish in poor condition (i.e. looser fish and ill fish that are not likely to recover in due course) from the sea cages for euthanasia is considered a good health management practice in aquaculture as it reduces the pool of potential disease carriers and spreading individuals (Ellis et al 2012). In addition, active euthanasia is also beneficial for welfare.…”