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.

Continuous drastic declines in natural sturgeon populations over the past 30 years plus a high market demand for caviar have led the way for sturgeon farming, mainly for the production of caviar. Russia, Iran, members of the European Union, China and the USA were among the first; however, for the very same reasons countries outside the natural range of sturgeons also became involved (e.g. Uruguay, Arabian countries, Israel, and more recently Vietnam). At present (2012), the total caviar output from aquaculture is estimated at 260 tonnes, a production that could increase to 500-750 t within the next 10 years. If these figures are realistic, the future of caviar trade will be determined mainly by demand-driven price structures, with the appearance of a new and evolving 'mass market' in addition to the traditional luxury high-priced market. Other issues are the uncertainties and opportunities in the market place. All of these issues indicate that this relatively new branch of the aquaculture industry faces similar growing pains as in previous developments (e.g. salmon farming) but within a shorter time frame. The same drive that gave the incentive to farm sturgeons also provided, since the early 1970s, the incentives to seek alternative products that could fill the void in caviar supplies and even create new market sectors. The various products currently found on the market have been divided into six categories: (a) true caviar (using eggs from sturgeons); (b) substitute caviar (eggs derived from other fish species or from other animals); (c) imitation caviar (caviar-like products constructed from other biological substances, imitating caviar in appearance and taste); (d) simulated caviar (produced by other biological substances to simulate only the taste of caviar, but not the appearance); (e) derivates (products that contain true caviar as a recipe component); (f) products with emotional associations to caviar (not related to caviar at all, but use the name as a marketing strategy to evoke a luxury image and infer a high value). At present, the eggs of more than 38 species of fish, besides sturgeons, and three species of other animals are used to produce substitutes. About 15 'caviar-like' preparations are used as raw materialssuch as fish flesh, seaweed, and others mixtures. Five products can be considered simulations; few use caviar as a component in their production recipes. A variety of objects (unrelated to caviar) are currently marketed, but use 'caviar' in their trademark. U.S.

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

A salt water exposure trial with juvenile Adriatic sturgeon, Acipenser naccarii, ( 5 months old; mean (* SD) weight = 56f28 g) was initiated by direct transfer from freshwater (FW) to brackish water (BW) of medium (310 mOsm.Kg-' = 11 %) or high salinity (640 mOsm.Kg-' = 23 960). Survival at 6 weeks and homeostatic regulation of plasma osmolality and ion concentrations demonstrated that A. naccarii of this age and/or size class possess the ability to adapt to hyperosmotic environments. Regulation of the osmotic status of body fluids was associated with differences in the number of mitochondriarich (MR) cells on the gill lamellae, whereby sturgeon in high salinities exhibited reduced MR cell numbers as compared with those in FW. Measurement of Na+,K+-ATPase activity in crude gill homogenates from the three groups of sturgeon revealed higher activity in sturgeon at salinities of 3 10 and 640 mOsm.Kgrelative to those in FW; significantly higher in the sturgeon at 640 mOsm.Kg-I. There were no differences in H+-ATPase activity amongst the groups, as measured on the same crude homogenates, but there was a significant increase in the ratio of Na+,K'-ATPase to H'-ATPase in the sturgeon in water at 640 mOsm.Kg-' relative to those in FW. There was a significant negative linear correlation between gill MR cell number and Na+,K+-ATPase activity. Apparently successful adaptation to BW was also indicated by similar low levels of serum cortisol, and similar rates of resting oxygen consumption, in all groups. Nonetheless, a growth study on triplicate groups of 40 tagged sturgeon in FW or BW at 600 mOsm.Kg-I (20 %) revealed that animals in BW grew less well and exhibited less efficient feed conversion. The results indicate that although sturgeon exhibit some morpho-physiological adjustments to hyperosmotic environments and are able thereby to regulate plasma ions and osmolality in BW at 310 and 640 mOsm.Kg-', they do not grow as well in BW at 600 mOsm.Kg-' as they do in FW and, in fact, died when disturbed by heavy activity near the tanks.

Specific growth rates, exercise respirometry, and swimming performance were compared in young-of-the-year Adriatic sturgeon (Acipenser naccarii) maintained in freshwater (FW) or acclimated to brackish water (BW) that was slightly hypertonic to sturgeon plasma, at a salinity of 11 g·L–1. Specific growth rate was significantly (17%) lower in BW than in FW. Sturgeon in BW also had a significantly (30%) higher standard metabolic rate than those in FW. In both groups, the relationship between swimming speed and oxygen uptake was described equally well by a linear or exponential equation, with a power relationship between swimming speed and net cost of locomotion and a linear relationship between tailbeat frequency and swimming speed. However, sturgeon in BW exhibited higher mean total oxygen uptake, net costs, and tailbeat frequencies than the FW group at any given swimming speed. There were, however, no differences in aerobic scope or maximum sustainable swimming speed between the FW and BW groups because the BW group exhibited a compensatory increase in active metabolic rate and maximum tailbeat frequency. The results indicate that FW is a more suitable environment than mildly hypertonic BW for young-of-the-year Adriatic sturgeon.

This paper provides a short overview on the status of sturgeon farming in Europe, covering most of the EU and former East Block countries. Production trends are presented along with a listing of species cultured in various countries. Principle culture systems are described and an opinion is presented on possible constraints and perspectives of sturgeon farming, including market opportunities.

In this study the first experimental trials of acclimation to salinities of the Italian sturgeon Acipenser naccarii are described. Preliminary observations regarding some morphological features of the gut, kidney and gills following exposure to 20 and 30‰ salinity are reported, and compared with those displayed by many teleosts in hyper-and hypoosmoregulation. Results are discussed with regard to the osmoregulatory mechanisms and to the physiological limits of adaptability of this species in the second year of its life cycle. Within the Acipenseridae, Acipenser naccarii is generally considered a euryhaline species, but nothing is known about its mechanisms of osmotic homeostasis. This species could be a good candidate for aquaculture in fresh and brackish waters owing to the recent success obtained in artificial reproduction.1995 The Fisheries Society of the British Isles

Data on the blood chemistry of a chondrostean fish, the Adriatic sturgeon (Acipenser naccarii), are reported as measured with different sampling procedures, and as related to rearing conditions and age. Serum cortisol, glucose, osmolality, Na', Cr, Ca" and total protein concentrations were measured. Reference values for the blood chemistry of farmed sturgeon were measured on samples from resting undisturbed animals collected via a chronic indwelling catheter in the dorsal aorta that was implanted under anaesthesia. Following 24h recovery from catheterization, serum cortisol, glucose and osmolality levels were 9.4 ng/ml, 58.8 mg/dl and 261.4 mOsm/kg, respectively. Furthermore, blood samples collected with the chronic indwelling catheters indicated that the surgical procedure of cannulation caused a stress response, with physiological changes that followed a pattern like that described in teleosts. Cortisol, glucose and osmolality were more sensitive to stress than the other variables measured. Sampling by cardiac puncture tended to be associated with elevated serum cortisol levels in older, larger sturgeon, but not in young fish. Greater capture, confinement and handling stress in older, larger, sturgeon may have been responsible for this and other age-related differences in blood chemistry values measured following cardiac puncture. Within the same age class, both rearing conditions and temperature affected cortisol, sodium and total protein concentrations significantly. Anaesthesia did not appear to reduce the degree of stress associated with cardiac puncture but altered serum ion concentrations. IntroductionThe levels of a suite of chemical constituents of the blood are