Biological characteristics of European Atlantic sturgeon, Acipenser sturio, as the basis for a restoration program in France

The European Atlantic Sturgeon, Acipenser sturio, has received increased attention in France because of population declines due to overfishing and deterioration of spawning grounds. Conservation of this species requires many actions, including publicizing the necessity to protect this fish and its habitats, investigations on catches and probable spawning grounds, and on artificial reproduction, which is still in an experimental stage. During its sea life, European Atlantic sturgeon occur from the Bay of Biscay to the Bristol Channel and North Sea. Presently, the number of young fish in the Gironde Estuary during summertime is low and the population has a unimodal age structure. At the time this paper was written, the last recorded reproduction of sturgeon in the Gironde system occurred in 1988 (new evidence of reproduction was discovered in 1995). Growth of young fish from the 1988 cohort was faster than that previously determined for others cohorts. Over our study period (1980–1994), the availability of wild broodfish declined. Successful artificial reproduction of wild-caught females requires an optimal physiological state; any delay decreases their reproductive potential. Acclimatization of wild-caught juveniles to fresh water was most successful when fish were transported and held upon arrival in low salinity water. For such wild-caught juveniles, the first food intake usually occurs several months after capture, but remains irregular. These findings will be used to improve ongoing efforts to restore A. sturio.     

Comparison of behavioral and physiological–biochemical indices in fingerlings of roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis> (L.) from the Ild River and Ild Bay in the Rybinsk Reservoir

It is found that the size–mass, physiological–biochemical, and behavioral parameters in roach fingerlings from the upper and lower (mouth) reaches of the Ild River differed during the autumn season. Compared with the roach from the upper reach of the river, the fingerlings of the same age from the mouth part have larger lengths and weights and a higher concentration of cations in the body. In experiments, the fish from the mouth part selected a lower (~4°C) temperature and showed a lower resistance to the water flow. The reason for differences in behavioral responses in two groups of juveniles of roach is probably, on the one hand, their physiological and biochemical characteristics and, on the other hand, the motivational component of fish behavior in different environments—hydrological, thermal, and hydrochemical conditions and different food items in geographically remote parts of the same river. It is assumed that in autumn roach fingerlings migrate from the littoral of the mouth part of the river into deeper parts under a decrease in water temperature before the downstream migration of the fingerlings in the rivers. This is probably due to the earlier achievement of the migration status of fingerlings from the mouth part than that in fish from the upper reach of the river and due to the peculiarities of their physiological state. Negative rheoreaction, manifested in the experiment in ~80% of the fish from the bay of the reservoir and ~55% of the fish from river, confirms the fish readiness to migrate and is likely due to the behavioral mechanism of fish migration from the littoral and downstream the river.     

Morphofunctional changes of the interrenal gland and of ultrastructure of chloride cells in intact and hypophysectomized juveniles of starred sturgeon <Emphasis Type="Italic">Acipenser stellatus</Emphasis> (Acipenseridae) in the course of adaptation to sea water

The impact of hypophysectomy on the state of the interrenal gland and ultrastructure of chloride cells of gills is investigated in 18-month old juveniles of starred sturgeon Acipenser stellatus in the process of its adaptation to artificial sea water (14.6‰). Hypophysectomized juveniles, similarly to intact juveniles, are able to support a relative stability of osmolarity of blood serum in the course of adaptation to sea water by transition from hyperosmotic to hypoosmotic type of osmoregulation. Changes in the investigated parameters of cells of the interrenal gland (volume of nuclei, areas of cells and of lipophilic vacuoles) occurring in the hypophysectomized and in intact specimens in the process of adaptation to sea water are generally similar, but have different dynamics. In contrast to many teleostean species, in acipenserids the hypophyectomy does not cause atrophy of the interrenal gland. The latter is incorporated in the process of regulation in the course of adaptation of fish to sea water. Hypophyecotmy results in partial destruction of organoids in some chloride cells of gills. However, when the fish are transferred to sea water, the structural changes occur in chloride cells characteristic of their transition to the excretory state. This may happen only at activation of the transport enzyme Na⁺/K⁺-ATPase of these cells by cortisol produced by the interrenal gland. In the absence of hypophysis, the functional connection of organs of the axis hypothalamus (ACTH-immunopositive cells of tuberal nucleus) → the interrenal gland → chloride cells is realized in the fish.     

Etho-biochemical mechanisms of early differentiation in juveniles of the Atlantic salmon <Emphasis Type="Italic">Salmo salar</Emphasis>

The social status of hatchery-reared juveniles of Atlantic salmon Salmo salar at the age of 11–19 months in conditions of lack of shelters was investigated experimentally. It was demonstrated that biochemical differentiation in such juveniles begins at the age of 13 months—one month before the first differences in the social status of fish and four months prior to the beginning of smoltification. The dominants occupy bottom areas with shelters and extrude the subordinates to the water column. The subordinates undergo smoltification or die from aggression of the dominants. Concentrations of dopamine, noradrenalin, and of their metabolites in the brain of fish in the beginning of smoltification were higher in the dominants and, by the end of smoltification, were higher in smolts. The social behavior of fish is considered to be one of the ethological mechanisms of differentiation of salmon juveniles into smolts and parr.     

Ontogeny of salinity tolerance and evidence for seawater-entry preparation in juvenile green sturgeon, <Emphasis Type="Italic">Acipenser medirostris</Emphasis>

We measured the ontogeny of salinity tolerance and the preparatory hypo-osmoregulatory physiological changes for seawater entry in green sturgeon (Acipenser medirostris), an anadromous species occurring along the Pacific Coast of North America. Salinity tolerance was measured every 2 weeks starting in 40-day post-hatch (dph) juveniles and was repeated until 100% survival at 34‰ was achieved. Fish were subjected to step increases in salinity (5‰ 12 h⁻¹) that culminated in a 72-h exposure to a target salinity, and treatment groups (0, 15, 20, 25, 30, 34‰; and abrupt exposure to 34‰) were adjusted as fish developed. After 100% survival was achieved (134 dph), a second experiment tested two sizes of fish for 28-day seawater (33‰) tolerance, and gill and gastrointestinal tract tissues were sampled. Their salinity tolerance increased and plasma osmolality decreased with increasing size and age, and electron microscopy revealed three types of mitochondria-rich cells: one in fresh water and two in seawater. In addition, fish held on a natural photoperiod in fresh water at 19°C showed peaks in cortisol, thyroid hormones and gill and pyloric ceca Na⁺, K⁺-ATPase activities at body sizes associated with seawater tolerance. Therefore, salinity tolerance in green sturgeon increases during ontogeny (e.g., as these juveniles may move down estuaries to the ocean) with increases in body size. Also, physiological and morphological changes associated with seawater readiness increased in freshwater-reared juveniles and peaked at their seawater-tolerant ages and body sizes. Their seawater-ready body size also matched that described for swimming performance decreases, presumably associated with downstream movements. Therefore, juvenile green sturgeon develop structures and physiological changes appropriate for seawater entry while growing in fresh water, indicating that hypo-osmoregulatory changes may proceed by multiple routes in sturgeons.     

Age dynamics of lipid status of juveniles of atlantic Salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.) from the Varzuga River

Heterogeneity of zero class (0+) of Atlantic Salmon Salmo salar from the compared biotopes of the Varzuga R. (the Kola Peninsula) is revealed by the content of TAG, PL, 18:2n-6,18:3n-3, the sum of monoenoic FA, and parameters of CS/PL and TAG/PL retained in elder age groups of parr (1+ and 2+). It depends on the quality of food resources and hydrological conditions. The increase in the level of PS, one of the principal regulators of activity of Na⁺/K⁺-ATPase—a key enzyme of osmoregulation—in parrs 1+ and, to a greater extent, in smolts is supposed to be the formation of one of the biochemical mechanisms of preadaptation of fish to a marine environment. Salmon juveniles 3+ differ from the fish of junior age groups in a higher content of PUFA (20:4n-6, 20:5n-3, 22:6n-3), a considerable decrease in TAG, in parameter TAG/PL, and the sum of monoenoic FA related to smoltification and preparation for life in a marine environment. Multidirectional variations of concentrations of minor phospholipids (PI, LPC, SPM) in salmon juveniles depending on age and habitat may indicate the change in viscosity of biomembranes and, accordingly, of activity of some enzymes bound with membranes.     

Feeding,development, and growth of juvenile perch <Emphasis Type="Italic">perca fluviatilis</Emphasis> in mesocosms in the presence of filter-feeding zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> pallas

Quantitative and qualitative changes in the feeding spectra and growth patterns are studied in the larvae and juveniles of perch in artificial water ecosystems (mesocosms) in the presence of a filter-feeding zebra mussel. At a stocking density of 0.75 kg/m², the presence of a zebra mussel leads to a change in the feeding conditions of zooplankton, to a decrease in its abundance in regards to critical values for fish feeding, to an increase in the abundance of organisms of macrobenthos in the food, and to the rapid transition of the fish to feeding on chironomids. As a result of these changes, the growth rate of perch larvae decreases, their development at step D ₁ is delayed, the differentiation of the juveniles by size is accelerated, their size and weight variability increases, and individual predators (cannibals) appear.     

长江口水域夏季鱼卵和仔稚鱼年间变化

基于2005年、2008年、2009年和2011年8月(夏季)在长江口水域(30°30'—31°45'N,121°15'—123°10'E)4个航次的浮游生物拖网资料,分析了长江口水域鱼卵和仔稚鱼的种类组成、数量分布特征及其年间变化。结果表明:4个航次采集的鱼卵和仔稚鱼鉴定到种的种类有17种,隶属于8目13科,以鲈形目种类最多,11种,其次是鲱形目,5种,其他各目种类均小于5种;种类数存在明显年间差异,2005年种类数最多(鱼卵3种,仔稚鱼8种),其次是2009年和2011年,2008年种类数最少(鱼卵1种,仔稚鱼5种)。优势种年间更替明显,长蛇鲻(Saurida elongata)、虾虎鱼(Gobiidae spp.)和中华小公鱼(Stolephorus chinensis)在2005年是优势种,2008年优势种为鳀鱼(Engraulis japonicus),2009年优势种为鳀鱼、寡鳞飘鱼(Pseudolaubuca engraulis)、虾虎鱼等,2011年虾虎鱼和小公鱼(包括小公鱼属未定种Stolephorus spp.和中华小公鱼Stolephorus chinensis)成为优势种。2005年鱼卵和仔稚鱼数量分布的密集区在嵊泗列岛附近水域,2008年鱼卵和仔稚鱼出现较少,未出现明显的数量密集区;2009年鱼卵数量较少,仔稚鱼数量较多,密集区主要分布在在长江口以外123°E附近水域;2011年鱼卵主要分布在在长江北支口门外附近水域,仔稚鱼在调查区内分布相对均匀。     

Evidence of sustained populations of a small reef fish on artificial structures. Does depth affect production on artificial reefs?

The length frequencies and age structures of resident Pseudanthias rubrizonatus (n = 407), a small protogynous serranid, were measured at four isolated artificial structures on the continental shelf of north-western Australia between June and August 2008, to determine whether these structures supported full (complete size and age-structured) populations of this species. The artificial structures were located in depths between 82 and 135 m, and growth rates of juveniles and adults, and body condition of adults, were compared among structures to determine the effect of depth on potential production. All life-history stages, including recently settled juveniles, females and terminal males, of P. rubrizonatus were caught, ranging in standard length (L(s)) from 16·9 to 96·5 mm. Presumed ages estimated from whole and sectioned otoliths ranged between 22 days and 5 years, and parameter ±s.e. estimates of the von Bertalanffy growth model were L(∞) = 152 ± 34 mm, k = 0·15(±0·05) and t(0) = -1·15(±0·15). Estimated annual growth rates were similar between shallow and deep artificial structures; however, otolith lengths and recent growth of juveniles differed among individual structures, irrespective of depth. The artificial structures therefore sustained full populations of P. rubrizonatus, from recently settled juveniles through to adults; however, confirmation of the maximum age attainable for the species is required from natural populations. Depth placement of artificial reefs may not affect the production of fish species with naturally wide depth ranges.     

Development of length–bimodality and smolting in wild stocks of Atlantic salmon, Salmo salar L., under different growth conditions

Growth dynamics of juvenile Atlantic salmon, Salmo salar L., from two sections of the Narcea River and one of the Esva River (Northern Spain) were examined in relation to the development of bimodality in their size–frequency distributions. Size–bimodality was clearer under intermediate growth (section A) than under relatively fast or slow growth. The proportion of fish entering the upper modal group increase with growth intensity. Composition of upper and lower modal groups became fixed prior to December, and at this time both groups separated on the 90–95 mm interval. Fish exhibiting smolt appearance in late March (larger than 130 mm) had already been upper group fish in December, while parr-like fish and those that remained in the river by May (potential 2-year-old smolts) had formed the lower modal group. Anadromous salmon catch in the Narcea River was mostly of previously 1-year-old smolts (97.6%), of which 94% were larger than 100 mm by their first winter. In the Esva River, slow growth of juveniles is consistent with a large proportion of 2-year-old smolts (47.9%) among anadromous salmon. Both juvenile samples and scale analysis of anadromous salmon indicate that 2-year-old smolts were larger than 1-year-olds. Early disappearance of the former (before March) is, at least, partially related to earlier migration of large fish, since sexual maturity of parr does not provide a complete explanation. The Narcea stock have a minimum length at smolting of about 130 mm and an optimum smolt size in the 155–175 mm interval. Mean smolt length did not vary although the winter length changed between years.     

The reproductive cycle of yellowfin bream, Acanthopagms australis (Günther), with particular reference to protandrous sex inversion

Yellowfin bream, Acanthopagrus australis , of all age classes were collected from Moreton Bay, Australia. The species possessed typical sparid ovotestes in which the testis and ovary occur in separate zones. During the spawning period (June-August) juveniles, functional males and functional females could be distinguished by the macroscopic appearance of the gonad. The sex ratio of males to females decreases with age, indicating protandrous sex inversion.
Histological and structural study of the ovotestis showed all fish have previtellogenic cells in the ovarian zone but only juvenile and male fish have developing spermatogenic cells in the testis. Most juveniles become functional males by the age of two years but a small proportion of juveniles develop directly into functional females (primary females). Protandrous sex inversion commences after the spawning period when male fish appear with spermatozoa and no other spermatogenic cells in the testis. During the period November-January male fish with no spermatogenic cells are common and a reduction in size of the testis occurs so that by March-April the ovotestis becomes structurally and histologically similar to the female ovotestis. Some fish remain functional males during their whole life-history (primary males). In functional females vitellogenic cells are present in the ovary only during the spawning period and the testis remains very small in size.     

Morphological changes during metamorphosis in cod (Gadus morhua L.), with particular reference to the development of the stomach and pyloric caeca

Metamorphosis in cod, Gadus morhua L., was investigated with respect to morphological changes in the alimentary tract (mouth, stomach and pyloric caeca) and external characters (finfold and fin development). Morphometric measurements and histological investigations were made on both larvae and juveniles and all fish lengths are given as standard length. Median unpaired fins started to develop when the fish were 9–10 mm in length. The larval median finfold was resorbed when fish reached a size of 11–15 mm. The vertebrae were formed in fish of 11–20 mm. The supraterminal mouth, seen in larvae <12 mm, changed gradually to a sub-terminal position in juveniles larger than 65 mm. The development of the stomach and pyloric caeca started at 15 mm and the juvenile form was seen in fish of 40 mm. The ability to store and grind food particles in the stomach developed gradually as fish increased in size from 20 to 40 mm. Compared to many other teleost species, cod juveniles are relatively large when the stomach and pyloric caeca become fully developed. These findings may have important implications for both start-feeding of cod larvae and the weaning of juveniles on to artificial diets.     

Is artificial habitat diversity a key to restoring nurseries for juvenile coastal fish? Ex situ experiments on habitat selection and survival of juvenile seabreams

Man‐made infrastructures have become ubiquitous components of coastal landscapes, leading to habitat modification that affects the abundance and diversity of marine organisms. Marine coastal fish have a complex life cycle requiring different essential habitats. One of these habitats is known as a nursery, a place where juveniles can settle in large numbers, survive, and grow to contribute to the adult population. Nurseries are mainly found in shallow, sheltered zones and are thus particularly impacted by urbanization, notably by harbors. The vertical featureless structure of docks is very unlikely to be used by juveniles, which need complex habitats to find food and shelter from predators. Recent attempts to rehabilitate the nursery function in such environments by using artificial habitats have proven efficient in increasing juvenile densities. However, nothing is known about the survival of juveniles in these habitats, preventing any conclusions on the effectiveness of this means of restoration from being drawn. Here, we set up tank experiments to test the relationship between habitat preferences and the survival rate of two species of seabream when facing stalk‐attacking combers. Habitat choice was consistent with survival results, indicating that artificial habitats might not represent unintended ecological traps for juveniles. However, the artificial habitats' effect on survival was variable between species. Therefore, our results suggest that habitat diversity might be of prime importance to sustain juveniles of different species and stress the need for the development of diverse artificial habitats to counteract the effects of seascape homogenization.     

An accurate tool for ageing Two‐spined Blackfish for use in determining timing of spawning in upland streams in the Brindabella ranges,ACT, Australia

To manage populations of threatened fish species in modified habitats and regulated rivers requires an understanding of their reproductive biology and spawning cues. In particular, accurate information about early life stages in these species can be used to facilitate programmes that maximise recruitment and breeding success. This study aimed to develop methods to accurately age early juvenile freshwater native fish, Two‐spined Blackfish, (Gadopsis bispinosus), to allow the determination of spawning date. This was accomplished through the examination of otolith microstructure in early juveniles. The age at which the first ring was deposited and the relationship between days and number of rings were determined using both field and aquarium trials. Field trials of marked juvenile otoliths revealed daily deposition of rings (1.02 ± 0.02 rings per day for fish sacrificed six days postmarking). The strength of this relationship lessened slightly as juveniles aged (0.92 ± 0.02 rings per day for fish sacrificed 13 days postmarking). The first otolith ring was deposited 7.50 ± 1.09 days after spawning. The enumeration of daily rings combined with knowledge of the commencement of ring deposition enabled accurate estimation of spawning date. The current study is the first to examine otolith microstructure in juvenile Two‐spined Blackfish allowing accurate determination of spawning date. While more research is required to accurately age older juveniles, this technique has the potential to precisely correlate spawning with environmental cues, facilitating better management of temperature and flow during breeding periods, potentially increasing spawning and recruitment of this endangered species.     

Development of ethologo-physiological differentiation between parrs and smolts of the Atlantic salmon <Emphasis Type="Italic">Salmo salar</Emphasis>

Dynamics of the level of monoamines and their metabolites in the brain of juveniles of the Atlantic salmon Salmo salar is investigated in the initial period of differentiation of the progeny into parrs and smolts. The first differences in the level of metabolism of noradrenaline (NA) and 5-HT arise in the optical tectum of the brain before the beginning of smolting. Appearance of the first signs of smolting in juveniles is accompanied by the increase of differences in the level of activity of HA-and 5-HT-ergic systems in the forebrain and hypothalamus. The first differences in the activity of the DAergic system between parrs and smolts were observed in the period of visible differences in fish coloration. In the same period, considerable differences in the level of adrenaline and noradrenaline in the fish blood were recorded. In experiments on a prolonged exposure of fish to a current of different intensity, it was shown that behavior and physiological response of the fish organism are different: in parrs, the stressogenous response is developed, they stop feeding, weight loss takes place, and they cannot withstand the water flow; smolts adapt to the current using heterogeneity of water movements.     

Heart Rate Variability in Healthy Six- to Sixteen-Year-Old Children

To study the age-related features of heart rate variability in children between the age of 6 to 16 years, cardiac rhythmograms of 5400 children were analyzed. It was found that parameters of the heart rate (M, SDNN, RMSSD, TF, VLF, and HF) in these children increase with age, changing in a wavelike way from year to year. Gender differences were observed in parameter M beginning from the age of 9; in parameters TF, VLF, and LF, the differences were observed beginning from the age of 11; and in parameters SDNN, RMSSD, and HF, the differences were observed from the age of 12 years. No differences between 16-year-old boys and girls in all the parameters of heart rate variability were found. It was shown that parameter VLF derived from ECG epochs of less than 5-min is suitable for physiological and clinical assessment. The obtained values of the parameters can be used in practice as reference standard.     

南方大口鲇幼鱼发育的初步研究

南方大口鲇的人工孵化鱼苗在11日龄时卵黄消失,转入营外生性营养的仔鱼阶段;23—26日龄仔鱼的主要外部器官分化完毕,转入稚鱼阶段;40—43日龄稚鱼除存在第二下颌须外,其余外形特征与成鱼相似,稚鱼阶段结束. 5月上旬在嘉陵江中采获到的当年幼鱼已发育到稚鱼阶段结束时期的水平;6—7月的当年幼鱼,当体长为151—177毫米时,第二下颌须消失.当年幼鱼体重和体长的关系为: W=e-10.87062L2.74257(N=77,r=0.9952)根据尾形、体色和须的数量的差异,可以区别南方大口鲇和鲇的当年幼鱼.       

Application of enriched <Superscript>137</Superscript>Ba tracer to mark juvenile Persian sturgeon (<Emphasis Type="Italic">Acipenser persicus</Emphasis>)

The present study evaluates the variations of ¹³⁷Ba abundance in pectoral fin spine of 1-month-old juvenile Persian sturgeon (Acipenser persicus) upon marking using the stable isotope approach. The marking of the fish was achieved by incorporation of ¹³⁷Ba²⁺ in the calcified lattice of the pectoral fin spine through substitution with structural Ca²⁺. This process was carried out by rearing juveniles in treatment tanks containing elevated concentrations of ¹³⁷Ba for 1, 3 and 5 days. The marked fish were then retained in natural abundance fresh and brackish waters, to evaluate the trend of exchange of ¹³⁷Ba from the fin spines. The abundance of ¹³⁷Ba in fin spines during marking and post-marking experiments were detected by inductively coupled plasma mass spectrometry (ICP-MS). The results showed that a significant isotope mark can be obtained with no mortality and 100% marking rate on the first day of exposure to the isotope. The marked juveniles maintained their isotopic signature for at least 25 days. Statistical analysis of the obtained ¹³⁸Ba/¹³⁷Ba ratios demonstrated that the successful incorporation of ¹³⁷Ba²⁺ in pectoral fin spines provides an effective marking method for Persian sturgeon restocking programs.     

Response of juvenile tench Tinca tinca (L.) to the anaesthetic 2-phenoxyethanol

The response of tench Tinca tinca aged 40–171 days post‐hatch (22–49 mm TL) to the anaesthetic 2‐phenoxyethanol was studied at 25°C. The lowest effective concentration of 2‐phenoxyethanol increased with age, while the highest safe concentration decreased. The fish aged 40 days post‐hatch required a significantly (P ≤ 0.05) shorter time to become anaesthetized than did older fish. The recovery time after 15 min of exposure to 2‐phenoxyethanol at 0.45 g dm^?3 was significantly shorter in the 40‐day‐old fish than in older fish. In juveniles of the same age, induction time or recovery time did not depend on their size or condition (Fulton's coefficient). At 25°C, 2‐phenoxyethanol at 0.5 g dm^?3 may be used to efficiently and safely anaesthetize T. tinca juveniles.     

Role of phospholipids in early ontogenesis of Arctic-Boreal species <Emphasis Type="Italic">Leptoclinus maculatus</Emphasis> (Stichaeidae)

The content of total phospholipids and their classes (phosphatidylinositol, phosphatidylserine, phosphatidylethanolamine, phosphatidylcholine, sphingomyelin) of muscles (flesh) and lipid sac of different developmental stages of young fish the daubed shanny, Leptoclinus maculatus from Kongsfjord (Svalbard, Norway) in winter was studied. The content of phospholipids in flesh decreases with age on account of phosphatidylcholine and phosphatidylethanolamine that probably related to their role in morphogenesis during differentiation of tissues and organs. The content of phospholipids is lower than reserve lipids in the lipid sac. The level of phospholipids in the lipid sac compared to flesh increases with age of fish reaching the maximum in benthic juveniles. Variations of minor phospholipids content of young fish of the daubed shanny indicate their participation in biochemical mechanisms of adaptation realizing in specific and varying Arctic conditions.