Environmental enrichment for fish in captive environments: effects of physical structures and substrates

Abstract

Structural environmental enrichment, that is, a deliberate addition of physical complexity to the rearing environment, is sometimes utilized to reduce the expression of the undesirable traits that fish develop in captivity. Increasing demands and regulations regarding usage of enrichment to promote fish welfare also make investigations on the effects of enrichment important. Here, we sythesize the current state‐of‐the‐art knowledge about the effects of structural environmental enrichment for fish in captive environments. We find that enrichment can affect several aspects of the biology of captive fish, for example, aggression, stress, energy expenditure, injury and disease susceptibility. Importantly, these effects are often varying in direction and magnitude, and it is clear that just addition of structure is not a solution to all problems in fish rearing. Each species and life stage needs special consideration with respect to its natural history and preferences. A multitude of different enrichment types has been investigated and many studies investigate several enrichment components at the same time, making comparisons among studies difficult. To the present date, the majority of efforts have been directed to investigate salmonid fish in stock‐fish hatcheries and cichlids from a basic research perspective. Some contexts are under‐studied with respect to environmental enrichment, for instance effects on results in basic research and welfare effects in display aquaria. There are many research opportunities left within this field. However, future studies could utilize experimental designs which make it possible to discriminate between effects of different environmental manipulations to a higher degree than what has been performed to this date.

Population biology of infectious diseases shared by wild and farmed fish

“…The challenges of infectious disease in fisheries and aquaculture have already spurred innovations to control disease and promote fish health (Pohlenz and Gatlin 2014;Jones et al 2015;Naslund and Johnsson 2016). The obvious example is the production of new pesticides, medicines, and vaccines (Lorenzen and LaPatra 2005;Shoemaker et al 2009).…”

Structural and Social Enrichment: Effects on the Morphology of a Tropical Hatchery Fish

“…Structural enrichment could also lead to a distinct morphology, but to a lesser magnitude. Additional studies should be conducted to improve enrichment techniques, by analyzing behavioral data and identifying the most appropriate structures, as the structural enrichment effect will depend on the species, life stage and the enrichment type (Näslund and Johnsson, 2014) …”

“…However, the low fishery yield and the precarious conservation status of native migratory populations in southern and southeastern Brazil indicate that this practice has not been satisfactory (Agostinho et al, 2007). The poor stocking efficiency can be largely explained by low survival rates after release (Maynard et al, 1994), as the released fish are more adapted to captive conditions and consequently ill-suited to live in the wild (Olla et al, 1998;Araki et al, 2008;Belk et al, 2008;Johnsson et al, 2014). Hatchery tanks are quite homogenous and presents high density and less variable population, lacking of predators and prey, but constant food availability by pellets, while in the wild variables are spatially and temporally unpredictable, including turbidity level, water flow and structural complexity provided by gravel, rocks, plants and trees (Johnsson et al, 2014).…”

“…The poor stocking efficiency can be largely explained by low survival rates after release (Maynard et al, 1994), as the released fish are more adapted to captive conditions and consequently ill-suited to live in the wild (Olla et al, 1998;Araki et al, 2008;Belk et al, 2008;Johnsson et al, 2014). Hatchery tanks are quite homogenous and presents high density and less variable population, lacking of predators and prey, but constant food availability by pellets, while in the wild variables are spatially and temporally unpredictable, including turbidity level, water flow and structural complexity provided by gravel, rocks, plants and trees (Johnsson et al, 2014). As a result, farmed fish differ from wild fish in several aspects, like morphology, exhibiting distinct colorations (Maynard et al, 1994), different body, head and fin proportions (Swain et (Taylor, 1986;Saraiva and Pompeu, 2016).…”

“…As a result, farmed fish differ from wild fish in several aspects, like morphology, exhibiting distinct colorations (Maynard et al, 1994), different body, head and fin proportions (Swain et (Taylor, 1986;Saraiva and Pompeu, 2016). Thus, the environmental enrichment of hatchery tanks has been proposed as a means of minimizing the effects of captivity on the morphology of farmed fish (Näslund and Johnsson, 2014). The aim of enrichment is to modify captive conditions to improve biological functioning (Newberry, 1995).…”