European sturgeon (Acipenser sturio L.) young of the year performance in different rearing environments –study within a stocking program

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 threemonth-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.

Effects of rearing practice on post-release young-of-the-year behavior: Acipenser sturio early life in freshwater

“…Fish size is an important factor influencing predation -smaller fish are at greater risk than larger ones (Dieperink et al 2001, Juanes et al 2002 -and traditionally-reared C1 fish were significantly the smallest among all treatments. However, we demonstrated in our study that fish size was not linked to the survival proxy and there is the possibility that low survival in this treatment is better explained by rearing condition effects (Carrera-García et al 2016). These results would be congruent with studies done on YOY lake sturgeon, where 3 mo old fish had fewer recapture rates when reared traditionally than under a more enriched approach (ca.…”

“…We suggest that the effects of rearing condition on exploratory behavior, as reported by Carrera-García et al (2016), may have resulted in these individuals traveling farther. Moreover, a correlation between fish size and distance moved was found only for en riched-reared fish.…”

“…Fish were reared in captivity until 92 d post-hatch (dph; 3 mo old) using 2 rearing methods: enriched and traditional (Carrera-García et al 2016). Traditional rearing was based on the protocol used to raise fish for stocking in the Gironde and captive stock supplementation (Chèvre et al 2011).…”

“…Enriched rearing consisted of small mesocosms that imitated the natural environment: tanks were located outdoors with a flow-through system of river water subject to natural photoperiod and temperature variations. This rearing condition also had variable water depth and current, and landscapes were created weekly using different substrates (Carrera-García et al 2016). Fish in both rearing methods were fed ad libitum with live artemia Artemia salina beginning 9 dph for 12 d, followed by a mix of artemia and defrosted bloodworms Chironomus sp.…”

“…Moreover, a correlation between fish size and distance moved was found only for en riched-reared fish. As these fish were reared under water-current conditions (Carrera-García et al 2016), they probably had better swimming performance, which is often positively correlated with size (Wardle 1977). Traditionally-reared fish were not trained to cope with water currents and thus whatever their size, their swimming capacity was probably low at release.…”