Conservation Aquaculture Of Dabry’s Sturgeon (Acipenser Dabryanus):Fitness For Survival Of The Fingerlings And Juveniles From Enriched Rearing Environment

In-situ conservation, ex-situ conservation and restocking are as the three major strategies for endangered fish species conservation throughout the world. The fish hatcheries are not only the final refuges of the endangered fishes, but also playing an important role in their natural resources rehabilitation by supplying the larvae or juveniles for the supplementary and re-introduction programmes and supplying thechnologies and knowledges for ex-situ conservation. Comparing with other vertebrates, fish is highly phenotypically plastic to the environment. Thus, obvious differences of biological, morphological, behavioral and genetic characateristics have appeared between fish from the hatchery and the wild, where the physical environment (such as flow regimes, bottom substrates and cover et. al.), biotic and social environment (such as the appearance of the different cohort, biotic diet, the appearance of the predators, high density of the same group,et. al.) obviously differ from each other. With the help of artificial selection and inbreeding, the population-specific biological and life-historical characteristics of the hatchery-rearing fish will loss and bring the potential ecological threats to the nature with rehabilitation programmes, which will be the great handicaps for the sustainable development of the domesticated populations and the wild. It has caused wide concern to regulate the traditional hatchery procedures for endangered fish conservation. Environmental enrichment can be broadly defined as any technique designed to improve the biological functioning of a captive animal via modifications to its environment. Such concept is just what the conservation aquaculture recommenders want to mention about the reforms of the conventional fish hatchery, and it will have a fundamental influence in future. This study aims at establishing the potential strategies for conservation aquaculture of the Dabry’s sturgeon (Acipenser dabryanus Dumeril,1869) with emphasis on the environmental enrichment technologies. The biological, ethological and physi-ecological fitness traits of the Dabry’s sturgeon (DS) were comparatively evaluated in the environmentally enriched rearing tanks and the traditional rearing tanks (control) with considering the flow, substrate, biotic diet, photoperiod and predators as the enriching parameters. The study finally supplied some suggestions and recommendations for the sturgeon hatchery reforms in future. The results of the studies are as follows:1. Effects of the environmental enrichment on biological characteristics of DSNegative influences of the flow on the growth of DS were found after long term rearing (30 days more) in the flow enriched group (V) than the static water group (control, Cv), which may link with the duration of training and the strength of the flow.The survival rates and growth rates of the DS were obviously lower in gravel (diameter 30-50 mm) enriched tanks (BG) than those in sand (diameter 3-5 mm) enriched tanks (Bs) and the conventional tanks with fiberglass bottom (CB). While the survival rates and the growth rates of the DS in Bs were almost same with those in Cs after long-term rearing. In short period (within 30 days), the TL, BL, FL, LB and FA of petrol fin and tail fin of DS in Bs were positively better than that in CB.No significant difference on the most growth parameters was observed between the DS fed with earthworm (F) and those feed with the formula food (CF). The positive effectiveness of the diets on the growth of DS was enhanced with the combinative effect of the flow regime. Under the flow circumstance, most morphological parameters of DS feed with earthworm were obviously higher than those in the static water and such differences were not observed when the DS were fed with formula food.The study also evaluated the potential effects of extreme photoperiod (totally dark or totally light) on the growth and development of the DS. The results showed that the survival rates in both totally dark (24D:OL, Dark) and totally light (0 D:24L, light) were obviously lower than those in the control group (12D:12L, CP) in short term (within 30 days),while after long term culturing (more than 80 days) the growth parameters were both higher in the Dark or Light than those in CP.2. The effect of the enriched environment on sense organ development of DSThe comparation of the measurable parameters of the microstructure of the sense organ of DS showed that the developments of the vision and olfactory organ were not significantly influenced by the flow. While the development of taste buds and the ampulla of lorenzini of DS were obviously different in V and CY. The numbers of the buds and its morphological characteristics in the barbels, upper lip lower lip and gills of DS in V were mostly larger than those in Cv. The maximum depth,width and areas of the ampulla of lorenzini of DS in V is obviously larger than those in Cv.The results showed the bottom substrate (sand) also had affected the taste buds development of DS. The numbers of the taste buds and its morphological characteristic in Bs were higher than those in CB. The difference of the morphological characteristics of the ampulla of lorenzini also observed in Bs and CB, while there is no similar trends in the different trial durations. No differences of the effect of bottom substrate on eye development were observed. Not enough data were obtained for evaluated the effect of bottom substrate on the development of taste buds of DS.The results also showed the differences in sense organ development of DS fed with biotic food (F) and the formula food(CF). The thickness of the olfactory epithelium and the number of primacy olfactory lamellae of DS in F were obviously higher than those in CF. The numbers of taste buds in barbels, upper lip and gill were obviously higher than those in CF. Not enough data were obtained for evaluated the effect of diets on the development of eyes of DS.Significant differences of vision organ development of DS were observed under the totally dark and totally light circumstance. The number of the single cones cells per area and the number of nuclei in the outer nuclear layer per area of DS in Light were obviously higher than those in Dark. The taste buds in lower lip and barbels of DS in Dark is higher than that in Light. The difference of the morphological characteristics of the ampulla of lorenzini was also observed in Dark and Light, while there were no similar trends in the different trial durations.3. The effects of environmental enrichment on the swimming and preference of DSThe results of experiment showed that the flow enriched environment can improve the swimming capacity of the juveniles of DS. Critical swimming speed (Ucrit), swimming endurance and the growth parameters of the juveniles in V and Cv were measured respectively. The results showed that the total length, fork length and wet weight of either 40-days old or 80-days old juveniles in V were higher than that in Cv, while without a significant difference (P>0.05). Survival rates of the juveniles in the early culturing stage (from 15 days-old to 40 days-old) in V is lower than that in Cv, which may linked with the non-suitable strong flow velocity in the V and the survival rate was nearly the same during the second culturing stage (from 40 days-old to 80 days-old). The Ucrit (13.2±2.9 cm/s, or 2.19±0.48 FL/s, n=30) of 40 days-old juveniles in V were observed significantly higher than those (10.2±3.5 cm/s, or 1.70±0.59 FL-/s, n=30) in Cv (P<0.05) and the Ucrit (48.5±6.9 cm/s, or 3.25±0.46 FL/s, n=20) of 80-days old juveniles in V were also obviously higher than that (35.9±8.5 cm/s, or 2.41±0.58 FL/s, n=20) in Cv (P<0.05). The swimming endurance (101.6±38.2 min, n=15) of 40-days old juvenile in V at the velocity of 20 cm/s (which represents 1.5-2.0 times of Ucrit) was obviously longer than that (72.4±38.2 min, n=15) in Cv.The results of water velocity preference tests showed that both of juveniles of DS in V and in Cv would like chose the flowing environment than the static water, while the juveniles of DS in V appeared more frequently in area of the higher water velocity than that in Cv and the juveniles of DS in V appeared less frequently in area of the lower water velocity than that in Cv.The results of bottom substrate preference tests showed that both of juveniles of DS in V and in Cv would like choosing the sand as the favorite substrate rather than the gravel, and their preference was not different in static water.While when they were in the flow, the juveniles of DS in V appeared more frequently in area of the gravel than that in Cv. The results mean that the juveniles of DS in V could have the more habitat choices than that in Cv when they were in the wild. So, the ecological fitness of the DS was improved in the flow enriched environment.Substrate preference tests of the DS from BG, Bs and CB showed that they congruously preferred sand and slippery fiberglass bottom to the gravel. The juveniles from DS would spend more time in the gravel area than that from the CB when there were only the sand and gravel substrate. Such differences meant the early experience with bottom substrate would benefit for improving their acclimatization in the natural substrate.Early diet experience also made difference on their choice of food. The results showed that juveniles of DS would like to choose the familiar food that they had experienced. The DS that were fed with formula food would like to choose formula food more than other diet. The DS that had fed with the earthworm would like to chose more of earthworm, while, they also would like to choose some other biotic diet such as the fish meat and shrimp meat instead. It means they have more opportunities to find food in the wild.DS from all groups exhibited the thickness behaviors to the newly introduced potential predator (Silurus meriaionalis) and most DS passed by the predator directly (PB), and only a small proportion of DS would change their direction when they saw the predator (CD) and a little proportion of DS would turn round (TR) when they saw the predator. The scaring training with chasing after the DS with the predator was conducted for 5 days and had got the positive results. After training, the PB reactions of DS from all groups were obviously lower than those before training and the proportion of TR and CD increased largely, which meant the anti-predator behaviors were improved by the training. We also found the distance from the predator of the DS form V and F groups were obviously larger than that from the Cv and Bs.4. The effect of enriched environment on physi-ecological fitness of DSComparation of the energy metabolism enzyme activities in muscles of DS in V and C showed that activities of ATPase,3-hydroxyacyl-CoA dehydrogenase (3HCoAD), cytochromeoxidase (CCO), Nucleoside diphosphate kinase (NDPK-A) in tail muscles of DS were enhanced in V compared with C. While in the stomach, citroyl synthetase (CS), CCO,lactate dehydrogenase (LDH), NDPK-A and Succinate dehydrogenase (SDH) in V were obviously lower than that in C. In aspect of heart muscle, only ATPase was observed obviously higher in V than that in C. The static dioxygen comsumption rate in V and Bs were both obviously lower than other groups.The GDF11 gene of DS were firstly cloned. GDF11 gene cDNA total sequence contained 1298 BP (not including Poly A) and its open reading frame was constructed of 1191 BP, encoding 396 amino acids. And 5’and 3’non coding region were19 BP and 88 BP respectively. By Signal P prediction it was found that DS GDF11 protein contains a signal peptide of 21 amino acids. No differences were found in the expression of mRNA of GDF11 gene in muscle, brain and liver of DS in V and C. While the expression of mRNA of GDF11 gene in gill and heart of DS in V is 4.70 times and 2.72 times of those in C, respectively.Different food types also had different effects on digestive enzyme activity of DS. The activities of pepsin in the stomach, foregut and hindgut of DS and the activities of lipase in the hindgut of DS fed with earth worm (F) were obviously higher than those fed with artificial formula food (CF). No differences were observed with the amylase activities of DS in F and CF. The study found that about 30%-40% of DS that fed with the biotic food will never fed with the formula food again and caused a consequent death.The pepsin and lipase activities of DS in V tend to be higher than that in Cv, the stomach amylase in V is significantly lower than that Cv, which indicated that the water flow had a certain role in promoting digestive ability of DS.5. Comprehensive evaluation ofeffectivness of environmental enrichment on DS’S fitness and its applicationThe results of this study showed that water flow, as an important environmental factor, plays an important role in behavior shaping and biological characteristics maintaining for the DS. Even though the flowing Water had certain negative effects on growth of DS, it also showed positive effects on promoting sensory organ development, improving the swimming ability, expanding the preferred habitat space, improving the abilities of DS to escape from the predators. The physiological and biochemical indexes, energy metabolism adaptation, growth differentiation gene expression and feeding adaptation characteristics from our results also showed the adaption of sturgeon to the flow environment.Early experience with the bottom substrate will benefit for wild fitness of DS with the improved adaption of DS to the different types of substrate. The pebble and gravel substrate not the sand will have negative effects on growth of DS and they will also do good for the sense organ development of DS.The growth of DS fed with biotic food (earthworm) were not quite different with DS fed with formula food. While biotic food can do good for the sense organ development of DS and for searching and preying on the wild biotic food as well. The results showed that early diet will influence their food preference in wild, which may link with the fitness of their digestive enzyme activities to their early experienced diet and consequently will affect their ability and efficiency to find and prey on food in wild.Based on what have learned from the experiments, some concepts of environmental enriching strategies and recommendations for improving the wild fitness of the DS for restocking were supplied. The studies will theoretically and practically benefit for the in-situ natural resource rehabilitation and ex-situ conservation of DS and will also support some basic ideas for conservation aquaculture for all species of acipenserids.