Changes in body composition associated with smoltification and premature transfer to seawater in Coho salmon (Oncorhynchus kisutch) and King salmon (O. tschawytscha)

Serum protein, glucose and fat levels were determined for Coho salmon parrs, freshwater smolts, seawater smolts, seawater stunts and freshwater desmolts. Liver and muscle glycogen, fat, protein and water concentrations were also calculated. Serum protein, glucose and fat levels were significantly lower in the freshwater smolts than in the parrs. Furthermore, both liver and muscle total fat levels were markedly decreased in the smolts, suggesting that smoltification is associated with increased catabolism. Smolts that failed to reach seawater by late summer reverted to a parr-like appearance and also regained the biochemical characteristics of parrs (high body fat and glycogen). Premature transfer of Coho presmolts into seawater caused impaired growth (stunting). Stunted Coho had higher muscle protein levels than normal smolts and parrs. Tissue water levels were not significantly different between stunts and normal seawater smolts, suggesting that the stunting phenomenon may not be caused primarily by osmoregulatory failure but may be due to shifts in metabolic patterns. In contrast to the pronounced changes seen in Coho salmon, transfer of King salmon to sea water did not result in increased catabolism of body reserves or in the production of stunts.     

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.     

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.     

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.     

Net ground speed of downstream migrating radio-tagged Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) smolts in relation to environmental factors

The downstream migration of Atlantic salmon (Salmo salarL.) and sea trout smolt (S. trutta L.) was investigated using radio telemetry in the spring of 1999 and 2000. Forty wild sea trout smolts, 20 F1 sea trout smolts, 20 hatchery salmon smolts and 20 salmon smolts from river stockings were radio tagged and released in the Danish River Lilleaa. The downstream migration of the different groups of fish was monitored by manual tracking and by three automatic listening stations. The downstream migration of radio tagged smolts of both species occurred concurrently with their untagged counterparts. The diel migration pattern of the radio tagged smolts was predominantly nocturnal in both species. Wild sea trout smolt migrated significantly faster than both the F1 trout and the introduced salmon. There was no correlation between net ground speed, gill Na⁺,K⁺-ATPase activity or fish length in any of the different groups. The migration speed of wild sea trout smolts was positively correlated with water discharge in both years. In F1 sea trout smolts, migration speed was positively correlated with temperature in 1999. The migration speed of salmon smolts did not correlate to any of the investigated parameters.     

Influence of shelters and food resources on smoltification of juveniles of the Atlantic salmon <Emphasis Type="Italic">Salmo salar</Emphasis>

Influence of feeding conditions and of the presence of a various number of shelters in basins on development of differentiation of juveniles of Salmo salar at the age 1+ and formation of smolts were studied under experimental conditions. The experiments had been carried out on groups of ten fish. The influence of investigated factors turned out to be significant. Under normal feeding four times a day, the quantity of formed smolts depends on the number of shelters: the more shelters that are available, the fewer smolts appear in groups. The presence of one shelter is a strong stimulant enhancing aggressive activity towards conspecific individuals, resulting in destruction of some fish in the group. Under feeding once a day, i.e., under food shortage, more fish perished, and the number of smolts decreased as the fish did not accumulate a sufficient energy potential for the morphophysiological transformation. One of the potential mechanisms of development of differentiation of fish juveniles into parrs and future smolts is discussed, based on domination of some fish possessing the individual territory and exclusion of subdominant specimens into open water as a result of social interaction.     

Osmoregulation in juvenile and adult white sturgeon,Acipenser transmontanus

Synopsis Blood samples from cannulated young adult (2.5–15 kg) white sturgeon, acclimated to San Francisco Bay water (24 ppt) had plasma values of 248.8 ± 13.5 mOsm kg⁻¹ H₂O, [Na⁺] = 125 ± 8.0 mEq 1⁻¹, [K⁺] = 2.6 ± 0.8 mEq 1⁻¹ and [CL⁻] = 122 ± 3.0 mEq 1⁻¹. Freshwater acclimated sturgeon had an osmolality of 236 ± 7, [Na⁺] = 131.6 + 4.4, [K⁺] = 2.5 ± 0.7 and [CL⁻] = 110.6 ± 3.6. Freshwater acclimated fish gradually exposed to sea water (increase of 5 ppt h⁻¹) had higher plasma osmolalities than did the bay water acclimated fish. These young adult sturgeon are able to tolerate transfer from fresh water to sea water as well as gradual transfer from sea water to fresh water. Plasma electrolytes in transferred fish are regulated, but tend to differ from long term acclimated fish at the same salinities. There is a gradual increase in the upper salinity tolerance (abrupt transfer) of juvenile white sturgeon with weight: 5–10 ppt for 0.4–0.9 g fish, 10–15 ppt for 0.7–1.8 g fish, and 15 ppt for 4.9–50.0 g fish. The ability of juveniles to regulate plasma osmolality is limited. The young adult fish are able to tolerate higher salinities (35 ppt) than juvenile sturgeon but probably are also characterized by low activity of the necessary ion exchange mechanisms in the gills which permit rapid adjustment of blood electrolytes with graduate change in external salinity.     

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.     

Migration of Atlantic Salmon, Salmo salar, Smolt through the Estuary Area of River Ellidaar in Iceland

Synopsis We tagged both wild and hatchery Atlantic salmon, Salmo salar, smolts from River Ellidaar (64 ° 08′ N, 21 ° 50′ W) with ultrasonic tags. We caught the wild smolts in a smolt trap and selected the largest individuals from the run. We implanted the transmitters in the abdominal cavity of the fish and then released them in River Ellidaar close to the estuary. We used four ultrasonic receivers; one in the river’s estuary, one outside the estuary and two further away on both sides of an island in the estuary zone. The receivers recorded all transmitters within a 600 m radius. The hatchery smolts were larger than the wild smolts. Some of the smolts were lost on the way through the estuary. Only 4 out of 9 wild smolts and 14 of 17 hatchery smolts were recorded all the way through. The tags and the tagging likely affected the survival of the smolts especially the smaller fish. There were no differences in the smolt migration between the 2 years of study and no differences in the migration behavior between the wild and the hatchery smolts. After being released the smolts stayed on average for 10 h in the river then migrated into the estuary were they stayed for 54 h on average. Then they migrated straight through the area to the sea at approximately 0.2 fish lengths per second. We recorded large differences in the migration.     

Effect of manipulation of the renin-angiotensin system in control of drinking in juvenile Atlantic salmon (Salmosalar L) in fresh water and after transfer to sea water

Drinking in Atlantic salmon (Salmo salar) juveniles was investigated in fresh water and following transfer to sea water. There was a significant effect of fish size on drinking, and smolts (20–30 g) imbibed about ten times less water than alevins of 0.2–0.3 g. Freshwater smolts drank at a rate of 0.15 ± 0.03 ml · kg⁻¹ · h⁻¹ and administration of doses of 10 or 20 mg · kg⁻¹ of papaverine (stimulator of the renin- angiotensin system RAS) or [Asn¹, Val⁵]-Angiotensin II (0.4 μmol · kg⁻¹) resulted in significant increases in drinking, while administration of the angiotensin converting enzyme inhibitor, enalapril (50 mg · kg⁻¹) had no effect on drinking. Transfer of Atlantic salmon smolts to 1/3, 2/3 and full strength sea water resulted in significant increases in drinking to 1.06 ± 0.12, 1.24 ± 0.0.16 and 3.89 ± 0.28 ml · kg⁻¹ · h⁻¹, respectively. In sea water, stimulation of the endogenous RAS by administration of papaverine (20 mg · kg⁻¹) resulted in a 20% increase in drinking, while administration of enalapril to doses of 50 and 200 mg · kg⁻¹ lowered drinking to 1.99 ± 0.48 and 0.32 ± 0.06 ml · kg⁻¹ · h⁻¹, respectively. All treatments were without effect on blood plasma levels of Na⁺ and Cl⁻ in fresh water, while in sea water smolts both stimulation and inhibition of drinking resulted in hemoconcentration of Na⁺ and Cl⁻. The role of the renin angiotensin system in control of drinking and hydromineral balance in Atlantic salmon is discussed. Accepted: 27 February 1997     

Interactions between endangered wild and hatchery salmonids: can the pitfalls of artificial propagation be avoided in small coastal streams?

Hatchery and wild juvenile populations of steelhead Oncorhynchus mykiss and coho salmon Oncorhynchus kisutch , in a small coastal watershed in central California, were sampled throughout the year in a stream and at a hatchery. Both species grew faster in captivity than in the wild. Hatchery fish of both species had elevated gill Na⁺, K⁺‐ATPase activity, and thus were ready to enter sea water when planted during the wild fish migration. Downstream migrant trapping and stream surveys indicated that hatchery smolts went to sea soon after planting, consequently avoiding the effects of competition and predation that commonly occur when hatchery‐bred juveniles are released. Adult steelhead were also sampled throughout the watershed. The return of hatchery steelhead was highly synchronized with that of wild steelhead, indicating that hatchery propagation had no adverse effects on the timing of the run. A disproportionate number of hatchery steelhead returned to the tributary where the hatchery was located, despite being planted throughout the watershed. Hatchery steelhead did not differ in mean age or size from wild steelhead. Observations of spawning indicated that hatchery and wild steelhead interbreed. Competition for mates or spawning substratum was rarely observed between hatchery and wild steelhead. Many of the problems commonly associated with artificial propagation can be avoided in small coastal watersheds when wild broodstock are used and fish are released as smolts.     

Determination of body shape variation in Irish hatchery‐reared and wild Atlantic salmon

Discriminant function analysis was used to distinguish morphologically between samples of parr, smolts and adult Atlantic salmon Salmo salar from several hatchery and river systems in Ireland. The effect of habitat shift was investigated in Atlantic salmon parr. Parr grown from the eyed‐egg stage with a non‐sibling group in a hatchery environment, came to resemble the mean body shape of their host hatchery Atlantic salmon stock more closely than that of a full sibling group grown at their natal hatchery. Wild Atlantic salmon smolts differed in shape from hatchery‐reared smolts. This difference was less pronounced, but still statistically significant when wild adults were compared with hatchery‐reared adults captured in the coastal drift‐net fishery after a year spent at sea. Rearing conditions had a significant impact on the production and growth of fish body shape. This in turn may have affected adaptability and survivorship of ranched Atlantic salmon in the marine environment.     

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.     

Protoplast Formation of the Coccolithophorid <Emphasis Type="Italic">Pleurochrysis haptonemofera</Emphasis> in Hypoosmotic K<Superscript>+</Superscript> Solution: Shedding of the Coccosphere and Regrowth of the Protoplast in Normal Medium

Both coccolith-bearing cells (C-cells) and naked cells (N-cells) of the coccolithophorid Pleurochrysis haptonemofera can grow in salinities of more than 7‰ (about 20% of a “normal” sea water salinity [35‰]), with the highest growth rates in salinities of more than 14‰. Microscopic observations of cells suspended in 100 mM NaCl (7‰) showed that, while N-cells were swelling uniformly all over the cell surface, C-cells were bulging the plasma membrane from the hole of the coccosphere at the apical (flagellar) pole of the cell. Effects of several cations and anions on the morphological change of C-cells under hypoosmotic pressure were investigated. When 100 mM K⁺ was used, protoplasts were released from the coccosphere completely in almost all the cells. This phenomenon was shown with K⁺ most effectively. The protoplasts could grow in the fresh medium and form the first coccolith within 9 h.     

Feeding of wild and hatchery reared Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.) smolts during downstream migration

In general, hatchery salmonid smolts experience higher mortality during migration than wild smolts, which is suggested to be due to domestication effects and that hatchery fish lack experience of the natural environment. However, possible differences in feeding during smolt migration between hatchery and wild smolts have rarely been addressed. We compared the number of feeding smolts and stomach fullness among wild Atlantic salmon smolts, hatchery-reared smolts released as 1-year-old parr, and hatchery-reared smolts released as 2-year-old smolts during their descent to sea in River Tornionjoki. In addition, estimations of prey selection among the smolt groups were conducted. A high proportion of wild smolts and smolts stocked as parr actively fed during the smolt migration. A lower proportion of smolts stocked as smolts was feeding and their stomach fullness were much reduced in comparison with the two other groups. The study also indicated that the feeding of migrating smolts is selective rather than opportunistic. In conclusion, this study suggests that stocked 2-year-old smolts may enter sea with an inferior foraging behaviour and it is a possibility that this may contribute to the observed low post-smolt survival in the Baltic Sea.     

Protein degradation in the skeletal muscles of parrs and smolts of the Atlantic salmon <Emphasis Type="Italic">Salmo salar</Emphasis> L.

This paper reports a study of the activity of calcium-dependent proteases (calpains) and proteasome in the skeletal muscles of parrs and smolts of the Atlantic salmon Salmo salar L. from the Indera River (the Kola Peninsula). It was demonstrated that the growth rate and protein mass accumulation during smoltification in salmonid fishes are inversely related to the activity of proteases in their muscles. It was noted that decreased protein degradation in the skeletal muscles of salmon juveniles serves as a mechanism ensuring the intensive growth and physiological maturity necessary for migration from the river to the sea.     

Reaction of osmoregulatory system in juveniles of Russian sturgeon <Emphasis Type="Italic">Acipenser gueldenstaedtii</Emphasis> (Acipenseridae) on influence of comatotropin of carp <Emphasis Type="Italic">Cyprinus carpio</Emphasis>

For the first time by the example of juveniles of Russian sturgeon Acipenser gueldenstaedtii Brandt, the role of growth hormone of hypophysis in the osmotic regulation of acipenserids was studied, also the process of transformation of reserve chloride was described. In Russian sturgeon juveniles, administration of growth hormone of carp Cyprinus carpio at a dose of 1 mg per 1 g body weight causes changes in the fine structure of numerous reserve (undifferentiated) gill epithelial cells and thus stimulates their transformation into mature chloride cells involved in transport of monovalent ions. Increase in the number of chloride cells, on account of reserve cells, was accompanied by higher enzymatic activity of Na⁺/K⁺-ATPase in gill homogenates of the injected fish adapting to a hyperosmotic environment of salinity 12.5‰ (403 mosm/l) than in the intact fish under the same conditions but without hormonal treatment. Morphophysiological changes observed in the injected juveniles provided the more efficient dynamics of blood serum osmolarity under saline exposure than that in the intact fish. Their serum osmolality during the maximum rise (24 hours after the transfer of fish into the water of 12.5‰ salinity) was lower (p <0.01), than that of the intact fish. The inclusion of growth hormone in the osmoregulatory process was established.     

Seaward migrating Atlantic salmon smolts with low levels of gill Na+, K+ -ATPase activity; is sea entry delayed?

Two groups of migrating wild Atlantic salmon (Salmo salar) smolts caught within a 1 week interval in the River Alta, northern Norway, were tagged with acoustic transmitters and measured for gill Na⁺, K⁺ -ATPase activity in order to compare their smolt status with timing of sea entry. The first group of smolts had low levels of gill Na⁺, K⁺ -ATPase activity and resided in the lower part of the river twice as long as the second group that had high levels of gill Na⁺, K⁺ -ATPase activity. This indicates that early migrating smolts may not be completely physiologically adapted for salt water and delay their sea entry, thereby also synchronizing their seaward migration with the later migrating smolts.     

The Condition of Ovaries in Hatchery-Reared Juvenile Summer- and Fall-Run Chum Salmon, <Emphasis Type="Italic">Oncorhynchus keta</Emphasis> (Walbaum, 1792), in Sakhalin Oblast

The condition of the ovaries in juvenile fall- and summer-run chum salmon prior to release was studied at five fish hatcheries that operate on Sakhalin Island. It has been found that juveniles released from different hatcheries, while having a similar body weight, may differ in the degree of development of their ovaries. Juvenile summer-run chum salmon showed a lower oogenesis rate at the hatchery with the warmest water and a higher oogenesis rate at the relatively cold-water hatcheries, compared to that of fall-run juveniles.     

Early life stage salinity tolerance of wild and hatchery-reared juvenile pink salmon Oncorhynchus gorbuscha

Salinity tolerance in wild (Glendale) and hatchery (Quinsam) pink salmon Oncorhynchus gorbuscha (average mass 0·2 g) was assessed by measuring whole body [Na⁺] and [Cl^?] after 24 or 72 h exposures to fresh water (FW) and 33, 66 or 100% sea water (SW). Gill Na⁺, K⁺‐ATPase activity was measured following exposure to FW and 100% SW and increased significantly in both populations after a 24 h exposure to 100% SW. Whole body [Na⁺] and whole body [Cl^?] increased significantly in both populations after 24 h in 33, 66 and 100% SW, where whole body [Cl^?] differed significantly between Quinsam and Glendale populations. Extending the seawater exposure to 72 h resulted in no further increases in whole body [Na⁺] and whole body [Cl^?] at any salinity, but there was more variability among the responses of the two populations. Per cent whole body water (c. 81%) was maintained in all groups of fish regardless of salinity exposure or population, indicating that the increase in whole body ion levels may have been related to maintaining water balance as no mortality was observed in this study. Thus, both wild and hatchery juvenile O. gorbuscha tolerated abrupt salinity changes, which triggered an increase in gill Na⁺, K⁺‐ATPase within 24 h. These results are discussed in terms of the preparedness of emerging O. gorbuscha for the marine phase of their life cycle.