Sturgeons seem to be frozen in time. The archaic characteristics of this ancient fish lineage place it in a key phylogenetic position at the base of the ~30,000 modern teleost fish species. Moreover, sturgeons are notoriously polyploid, providing unique opportunities to investigate the evolution of polyploid genomes. We assembled a high-quality chromosome-level reference genome for the sterlet, Acipenser ruthenus. Our analysis revealed a very low protein evolution rate that is at least as slow as in other deep branches of the vertebrate tree, such as that of the coelacanth. We uncovered a whole-genome duplication that occurred in the Jurassic, early in the evolution of the entire sturgeon lineage. Following this polyploidization, the rediploidization of the genome included the loss of whole chromosomes in a segmental deduplication process. While known adaptive processes helped conserve a high degree of structural and functional tetraploidy over more than 180 million years, the reduction of redundancy of the polyploid genome seems to have been remarkably random.

Summary The over‐exploitation both of natural and enhanced sturgeon stocks for caviar production along with serious habitat deteriorations has led to drastic declines in the natural populations. As a consequence, IUCN in 1997 listed all commercially utilised sturgeon species world‐wide in Annex II of the CITES regulations, thus requiring internationally agreed quotas for trade in order to promote protection. Demands for caviar on traditional export markets (Europe, US, Japan, Russia, and China) based on trade data from the 1980s and 1990s were extrapolated into the future to range from 300 tonnes to a maximum of 2000 tonnes annually. Historically, international trade comprised 500 tonnes per year with a marked proportion of resale over 2 years following the catch. If these trade figures are a realistic reflection of the market, the future of caviar trade will mainly be determined by demand‐ driven price structures. The feasibility of caviar production from aquaculture was already assessed in the 1980s, predicting an increasing importance on world markets. Russia, Iran, the European Union, and USA were among the major producers and consumers in the past. New entities in the range states as well as outside are increasingly contributing to the market, resulting in a substantial influence on the structure of the industry. The present total output of about 80–100 tonnes of caviar from aquaculture is now already exceeding the 2006 legal caviar yield from fisheries in the Caspian area (primarily supported by ocean ranching) while being close to the 2007/2008 quotas. Future trends for large scale caviar production are discussed, taking into account some of the scenarios the industry is most likely to face, including uncertainties in the market (e.g. rapid production increase and market sensitivities to overproduction with price structure effects, stress effects in production costs, reduced profit margins, product diversification; growing competition from alternative products) and opportunities (decreasing pressures on natural stocks; improved image) of this relatively new branch of aquaculture.

This paper presents an update on the global sturgeon and caviar production until 2017, attempting to continue previous efforts on summarizing the global trends in these markets. For the current update, an expanded data base was derived from questionnaires sent to 86 regional contacts in 46 countries, mostly farmers or scientists, and personal interviews. A total of 2,329 commercial sturgeon farms were recorded by 2017 globally, which represented an increase by 7% compared to 2016.Of these farms 54% were located in China, followed by Russia (24%), the Middle East (8%), the Far East (7%) and Europe (6%). Among the rearing technologies flow-through (FT) systems (36%) were most common, followed by recirculation aquaculture systems (RAS) (21%), cages (18%), mix FT/RAS (11%), and ponds (6%). In total the aquaculture sturgeon biomass production peaked at about 129,608 t in the year 2015, with a decline to 119,979 t in 2016, and to 102,327 t in 2017. China contributed about 79,638 t to the overall production in 2017, followed by Russia (6,800 t), Armenia (6,000 t), Iran (2,514 t), and 52 other countries with less than 1,000 t each.This production exceeded the fishery harvest during the 1970-1980s by more than four times. Of the 25 species of Acipenseridae, 13 pure species and four hybrids were farmed for meat with Acipenser baerii dominating production in 2016 with a share of 39.5%, followed by the two hybrids, Huso dauricus × Acipenser schrenckii and A. baerii × A. schrenckii (35.6%), as well as A. schrenckii (10.2%). Global caviar production increased during the last years and the production for the year 2017 amounted to approximately 364 t. China contributed more than 100 t to the overall production in 2017, followed by Russia (49 t), Italy (43 t), France (37 t) and diverse other countries. The species composition in caviar production in 2016 was dominated by A. baerii (31% of the total volume), followed by Acipenser gueldenstaedtii (20%), the hybrid H. dauricus × A. schrenckii (13%), and Acipenser transmontanus (12%), while other species jointly contributed 24% to the overall yield. The trends of sturgeon meat and caviar productions of the last 5 years and the forecasts for the future suggest a short-term scenario in which the demand remains lower than the supply. In order to absorb the growing production, the market will have to be expanded by targeting new market segments. K E Y W O R D Saquaculture, markets, production data, sturgeon

Although analyses of intraspecific variability are an important prerequisite for species identification assays, only a few studies have focused on population genetics and historical biogeography of sturgeon species. Here we present the first study on genetic variability of the last remaining Adriatic sturgeon, Acipenser naccarii, derived from mitochondrial and nuclear DNA. Our mitochondrial DNA analyses arranged individuals into three distinguished mitochondrial DNA haplogroups (Po1, Po2 and Buna). Two haplogroups (Po1 and Buna) were correlated to geographical distribution, whereas the third (Po2) was not. It was, however, very closely related to one lineage of its Ponto-Caspian sister species, A. gueldenstaedtii. The distribution of nuclear markers (microsatellites and amplified fragment length polymorphism) was strongly correlated to geographical distribution. An assignment test based on nuclear data placed no specimen of A. naccarii to A. gueldenstaedtii and vice versa. Therefore, the presence of gueldenstaedtii-like haplotypes within the Po population is either the result of a postglacial introgression or an ancestral polymorphism and does not indicate a hybrid population. The most valuable tool for forensic species identification purposes is one diagnostic deletion separating all A. naccarii from A. gueldenstaedtii. As both A. naccarii populations are genetically differentiated, stocking of sturgeon from the Po River in Italy into waters of the Buna River would jeopardize the genetic differences between both populations and should thus be avoided.

The physiological and behavioural responses of early life phases in American Atlantic sturgeon (Acipenser oxyrinchus) towards sand and gravel substrate were examined during the first 15 days post-hatch. The free embryos were reared in circular tanks with approximately 30% of the bottom surface covered with either coarse gravel or sand. A group reared in tanks without additional substrate served as a control. Diurnal differences in activity patterns were observed. Substrate use by the free embryos revealed significant differences during the first 5 days post-hatch, being higher in the gravel group than in the sand group. The results in size of the free embryos revealed significant differences, with the gravel group showing the lowest total length and wet mass until the onset of exogenous feeding -although dry mass and energy contents were highest. In contrast, length and wet mass during yolk sac absorption were highest in the control group, but energy content at onset of exogenous feeding was 14% lower compared to the gravel group. The onset of exogenous feeding in the gravel group had a 1-day delay when compared to the two other treatments. On day 14, following the successful establishment of exogenous feed uptake, the specific growth rate in wet mass (SGR) for the gravel group (0.250 ± 0.088) exceeded those of the two other treatments (sand 0.132 ± 0.038 and control 0.095 ± 0.020) significantly (DunnÕs n = 10 and n = 5, P < 0.05), indicating a compensational growth pattern. Cortisol concentrations in free embryos did not differ significantly among the three groups, providing no evidence for differences in stress levels among the three treatments until onset of exogenous feeding. The results strongly suggest that gravel is the most beneficial substrate for free embryo development of American Atlantic Sturgeon, impacting the physiological performance of their early life phases and reducing predation.

The chemical and biochemical composition of caviar in 22 specimens of wild caught and of 2 farmed animals were measured. The results include grain size, protein and fat content, fatty acid composition of triglycerides and phospholipids, as well as the concentrations of relevant heavy metals and chlorinated hydrocarbons. The average protein content varied between 26.2 and 31.1% (wet weight) and fat from 10.9 to 19.4% (wet weight) with lowest values for caviar from farmed sturgeon. The triglycerides and phospholipids contained more n-3 fatty acids, especially eicosapentaenoic and docosahexaenoic acid than n-6 fatty acids. The copper and zinc concentrations varied between 1.20 and 1.69 and 10.3 and 12.4 mg/kg (wet weight), respectively. These values reflect the elevated requirement of sturgeons for these components. Lead content varied between 0.06 and 0.15 mg/kg (wet weight). The cadmium concentrations were less than 5 micrograms/kg (wet weight) leading to the conclusion that no accumulation took place in the eggs. The concentrations of sigma DDT and sigma PCB were extremely high in caviar from Huso huso compared to the samples of the other species thus reflecting the different food habits leading to increased bio-accumulation.

Attention directed at different species by society and science is particularly relevant within the field of conservation, as societal preferences will strongly impact support for conservation initiatives and their success. Here, we assess the association between societal and research interests in four charismatic and threatened species groups, derived from a range of different online sources and social media platforms as well as scientific publications. We found a high level of concordance between scientific and societal taxonomic attention, which was consistent among assessed species groups and media sources. Results indicate that research is apparently not as disconnected from the interests of society as it is often reproached, and that societal support for current research objectives should be adequate. While the high degree of similarity between scientific and societal interest is both striking and satisfying, the dissimilarities are also interesting, as new scientific findings may constitute a constant source of novel interest for the society. In that respect, additional efforts will be necessary to draw scientific and societal focus towards less charismatic species that are in urgent need of research and conservation attention.

1.Although marine mammals are considered to be disproportionately threatened compared with terrestrial mammals, and research data on marine mammals are limited, few attempts have been undertaken to analyse overall marine mammal research effort. 2. We applied the bibliometric approach to evaluate global trends in research on pinnipeds and cetaceans and attempted to evaluate the distribution of publication output with respect to spatial, taxonomic and conservation status-related patterns. 3. Results show that global marine mammal research is disproportionately directed towards less endangered species. There is an uneven scientific focus among different cetacean and pinniped groups. A spatial asymmetry in research effort was also observed: a negative relationship exists between research allocation and regional marine mammal species richness. Cetacean species with larger ranges and pinniped species with larger population abundances tend to be better studied than others. 4. The observed patterns may exist because researchers have limited access to specimens of highly endangered species and to species found in less accessible habitats. Researchers from high-income countries may also focus their research on species geographically close to them, and other economic considerations may lead to research bias. The observed unevenness of research allocation may result in a lack of information needed by policy-makers and resource managers for the development of sound conservation and restoration measures, and thus in reduced effectiveness of policies and management practices.