Abstract
The European sturgeon is critically endangered and the French ex-situ conservation approach involves developing a captive stock to produce offspring for release to boost natural populations. The purpose of our study was to assess the effects of rearing environment before stocking on the survival, growth, and behavior of three-month-old sturgeons from two different crossings. Enriched rearing was designed to mimic the variability of the natural environment using river water, natural photoperiod, substrate, variable water current and depths. Traditional rearing was carried out with bare tanks, underground water, dark conditions, without current and at constant depth. Fish survival was determined monthly and growth was estimated weekly. Behavior was assessed with exploration and novel prey tests in solitary using video tracking. Results demonstrated that enriched condition resulted in bigger fish from the first month. Growth curve analysis revealed that enriched environment made both fish crossings grow in a similar manner. In contrast, crossings growth differed in traditional rearing which may reflect a genotype-environment interaction. Behavioral data highlighted that enriched-reared fish were slower to explore a new environment but more individuals engaged on doing so than traditional-reared fish. Results also showed that survival was high (>80 %) during all the trial. However, survival was lower during the second month in enriched environment. Our findings advocate for the integration of enriched rearing practices within the juvenile production for release in order to boost the performance linked to fitness. Stocking practices and life history research must work together to favor adaptive aquaculture approaches, which support species conservation.
Highlights
Most of the 25 species of sturgeons are believed to be at risk (Birstein 1993; Billard and Lecointre 2000), and 72 % of the family are considered Bendangered^ or Bcritically endangered^ according to the IUCN status (IUCN 2015)
The aim of the present study was to assess the effects of enriched rearing on the survival, growth and behavioral performance of three-month-old sturgeons belonging to two different crossings
Mortality in enriched rearing conditions decreased to 1.12 % during the third month, Table 4 Rate of monthly survival according to treatment
Summary
Most of the 25 species of sturgeons are believed to be at risk (Birstein 1993; Billard and Lecointre 2000), and 72 % of the family are considered Bendangered^ or Bcritically endangered^ according to the IUCN status (IUCN 2015). The species has a complex life cycle involving migration periods associated with habitat shifts (Castelnaud et al 1991; Rochard et al 2001; Acolas et al 2011a, 2012). The reproduction occurs in rivers between May and June, following which juveniles migrate to estuaries in the first year of their life. They remain and grow in estuaries for several years. The specific needs of this migratory species with regard to habitat, as well as vulnerability during migration, due to overfishing and habitat degradation are major factors involved in population collapse over the past few decades (Rochard et al 1990). One species restoration action consists of developing a captive stock to produce offspring for release in river systems in an attempt to boost natural populations (Chebanov et al 2011; IUCN/SSC 2013)
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