Trout Smolts Research Articles

Gill Na +–K +-ATPase activity and hypoosmoregulatory ability of seaward migrating smolts of anadromous Atlantic salmon ( Salmo salar), sea trout ( Salmo trutta) and Arctic char ( Salvelinus alpinus) in the Hals river, northern Norway

Gill Na +–K +-ATPase activity and hypoosmoregulatory ability of seaward migrating smolts of anadromous Atlantic salmon, sea trout and Arctic char were compared in a river system where all three species co-exist. Migrating Atlantic salmon and Arctic char were of similar size (mean lengths 13.3 and 14.6 cm, respectively) whereas the trout smolts were significantly larger (mean length 19.1 cm). The char smolts had the lowest condition factor and the trout smolts the highest. Migrating smolts of all three species had similar high gill Na +–K +-ATPase activity. The mean plasma Cl − concentrations after 24 h in seawater were not significantly different between Atlantic salmon and sea trout (about 150 and 160 mM, respectively), whereas these of Arctic char had significantly higher mean concentrations (about 180 mM). Smolts of both Atlantic salmon and sea trout in river Halselva in northern Norway were pre-adapted to seawater, perhaps the salmon smolts somewhat better despite their smaller body size. The small-size, first-time migrants of the Arctic char were not pre-adapted to life in full-strength seawater.

Smolting of sea trout ( Salmotrutta L.) in northern Norway

Seawater tolerance and development of the hormones thyroxine and cortisol were studied in hatchery-reared 2-year old sea trout ( Salmo trutta L.) smolts during the smolting period in 1995. The fish were reared under a simulated natural photoperiod and ambient water temperature. The fish were divided into two size groups. Fish from the small size group (mean 180 mm, range 143–210 mm) had an increasing seawater tolerance from the first sampling time, passing a plasma chloride value of 160 mmol l −1 by the end of June. This group also showed a peak in plasma thyroxine and plasma cortisol concentrations by the middle of May and by the end of June, respectively. Sea trout from the large size group (mean 199 mm, range 172–228 mm) given the same light and temperature regimes as the small size group established their seawater tolerance about 2 weeks before the small size group. Also, the osmoregulatory capacity of fish from the large size group was better when compared to the small size group. It is concluded that fish size is important for the development of the hypoosmoregulatory capacity in sea trout. It is also shown that sea trout develop the same hormonal pattern (thyroxine and cortisol) as other salmonid species during the smolting period.

Juvenile recruitment and smolt output of brown trout ( Salmo trutta L.) and Atlantic salmon ( Salmo salar L.) from a lacustrine system in western Ireland

A combination of electrofishing of feeder streams and shore seine netting of two lakes in a salmonid fishery in Burrishoole, western Ireland provided evidence of extensive use of lacustrine habitat by juvenile Atlantic salmon and brown trout. Mean densities of 0.024 trout and 0.002 salmon m −2 were recorded in L. Bunaveela (46ha), and 0.010 trout m −2 and 0.010 salmon m −2 in L. Feeagh (410 ha). Appearance of 0 + salmon and trout in summer seine net catches indicated early downstream movement of fry from inlet streams to lake inshore areas which also provided nursery habitat for older age classes. Total trap records of salmon and sea trout smolts migrating from Burrishoole catchment since 1970 were used to provide one of the first published estimates of smolt production from a lacustrine catchment in temperate Europe. Trout and salmon smolt output from Burrishoole was shown to have declined by about 50% since records began. Current levels of production are estimated at about 4 sea trout smolts ha −1 (0.4kg ha −1) and about 13 salmon smolts ha −1 (0.3 kg ha −1).

Reduction of brown trout, Salmo trutta L., salmon, S. salar L., and rainbow trout, Oncorhynchus mykiss (Walbaum), smolt bycatches in eel pound nets

Two types of bycatch reduction devices (BRDs) were tested in the Randers Fjord, Denmark, aimed at deflecting the surface‐oriented smolts of brown trout, Salmo trutta L., salmon, Salmo salar L., and rainbow trout, Oncorhynchus mykiss (Walbaum), before they became trapped, while retaining the catches of eel, Anguilla anguilla (L.). The methods tested were: a) placing a floating guard net between the wings; and b) submerging the pot net (i.e. last enclosure before fyke net) 55–100 cm below mean sea level. After each haul the pound net‐setups were changed from the control to one of the types of BRD, and vice versa. Both methods significantly reduced the bycatch of brown trout smolts, while catches of legal‐sized eels were not affected. Submerging the pot net reduced smolt catches of all species; mean reductions were 91.1% for brown trout, 74.5% for rainbow trout, and 86.1% for salmon.

Frequency of occurrence of acanthocephalans (Acanthocephala) and cestodes (Cestoda) in alimentary tracts of the sea trout smolts (Salmo trutta m. trutta) grown in the drainage area of the river Rega and their impact on fish condition

The present paper demonstrates results of analysis of 247 alimentary tracts of sea trout smolts (Salmo trutta m. trutta) grown in the drainage area of the river Rega (Pomerania). Frequency of occurrence of acanthocephalans and cestodes in the alimentary tract was determined, as well as their impact on fish condition.

Monitoring fish movement patterns in a reservoir using horizontally scanning split-beam techniques

Horizontally scanning split-beam hydroacoustics was used to monitor downstream migrating juvenile salmon and steelhead trout smolts (Oncorhynchusspp.). The study was conducted in the reservoir of Rocky Reach Dam on the Columbia River (Washington, USA). The objective was to determine the movement patterns of smolts as they migrated through the reservoir. Scanning split-beam hydroacoustic techniques and three-dimensional target tracking were combined with remote multiplexing with the aim of investigating smolt movement patterns in the reservoir. The trajectory profiles, target strength distributions, and horizontal distributions of the smolts were estimated for each of six different aiming configurations utilizing six different elliptical split-beam transducers. The results of this study were used to determine the optimal location for installing a surface collector and bypass system. This system will be used to collect and bypass smolts past the dam, a safer alternative to passing through the turbines. The results showed that fish migrated downstream primarily along the east side of the reservoir, concentrated in the upper water column. Few fish were seen migrating down the western shoreline. At the southern end of the reservoir, there were areas where the fish congregated into relatively large schools before proceeding on their downstream migration. Following this study, a smolt bypass system has been installed and is currently being evaluated.

The performance of sea trout, Salmo trutta L., stocks from the Burrishoole system western Ireland, 1970–1994.

Abstract Since 1975, with partial recoveries in 1979 and 1984–1986, the numbers of finnock and adult sea trout, Salmo trutta L., in the Burrishoole system, western Ireland, have declined. The population decreased sharply from 1987, and collapsed in 1989 and 1990. Finnock were virtually absent in 1989 and one‐year maidens equally so in 1990. Sea trout smolt recruitments from 1992 to 1994 were the lowest recorded since 1970. The modal fork length of finnock decreased from 28 cm in 1987 to 26 cm in 1990. Up until 1989, the percentage return of smolts, as finnock, ranged from 11.4 to 32.4%. In 1989 a minimum was reached at 1.5%, with values of 10.0, 3.7, 7.4 and 9.9% from 1990 to 1994. Marine survival of smolts, to total first return to fresh water, historically ranged from 19 to 66%. Survival dropped to 1.8% in 1989. Observed changes in the structure of the sea trout population and the collapse in marine survival suggest that the current west of Ireland sea trout problem is based in the marine habitat.

Biological characteristics of sea trout smolts (Salmo trutta m. trutta L.) grown in the River Gowienica catchment area

This paper examines length, length in the period of descending, weight, length-weight relationship, factor condition as well as the period of descending during 24 hrs of the sea trout smolts grown in the Pomeranian catchment area of the Gowienica River.

Biological characteristics of sea trout smolts (Salmo trutta m. trutta L.) grown from fry released in the Stream Osówka

Biological characteristics of sea trout smolts (Salmo trutta m. trutta L.) grown from fry released in the Stream Osówka

Artificial reconditioning of wild sea trout, Salmo trutta L., as an enhancement option: initial results on growth and spawning success

Abstract Following a sea trout stock collapse in 1989 and 1990, wild sea trout kelts were successfully reconditioned in brackish water using semi‐moist pellets and a commercial broodstock diet. The on‐growing of wild sea trout smolts was not so successful. Natural mortality was 12.9%, and 36.1% of the fish failed to adapt to the artificial diets: 82% of these were smolts. Instantaneous growth was highest from June to August (0.74%), with an overall rate for April to September of 0.51%. At the end of the first year. 36 females and 26 males matured; 34 females, with a mean fork length of 33.2 cm, were stripped yielding 22860 ova at a mean rate of 682 ova per female or 1586 ova kg‐1 body weight. The survival of green ova to eyed ova was 90–98%, and survival from green ova to hatched alevin was 95%.

Period of downstream migration of sea trout (Salmo trutta L.) smolt grown in Gowienica River

The period and intensification of downstream migration of sea trout smolts (Salmo trutta L.) grown in natural condition in the drainage basin of (Gowienica River, being a part of lower Odra system (in 5 consecutive years: 1980-1984), as well as water temperature in the lower section of Gowienica in this period is demonstrated in the present paper.

The movement of wild sea trout, Salmo trutta L., smolts through a river estuary

Abstract The movement of sea trout. Salmo trutta L., smolts through the estuary of the River Avon, southern England was studied using miniature 300 kHz acoustic transmitters and an array of strategically placed acoustic sonar buoys. Sea trout smolts were trapped 3.25 km above the head of tide as they moved downstream and the transmitters were surgically implanted into the peritoneal cavity of the fish. Subsequent movement of the smolts through the estuary was predominantly nocturnal and occurred mainly during an ebb tide or the period of slack water between two high waters. During the hours of darkness the ground speed of the smolts through the estuary was similar to that of passively drifting objects. However, where movement did occur during daylight hours ground speeds of smolts were significantly slower. Vertical salinity profile measurements of the estuary indicated that individual smolts may have experienced salinities ranging from fresh to 100% sea water during their migration. The behaviour of the smolts is discussed in relation to the possible environmental and physiological cues controlling the estuarine migration.

Predation and dietary habits as possible explanations for poor return rates of stocked sea trout from the river Aurland

The river Aurland was earlier known to be the best Norwegian river for sea trout fishing. Today, after regulation for hydroelectric purposes, the catch has fallen dramatically despite releases of hatcheryreared sea trout smolts and a remaining natural production. A field experiment in May–June 1991 indicated heavy predation on smolts leaving the river. In the river Aurland the water discharge during the smolt migration period is greatly reduced as compared to the situation prior to regulations. Other authors have shown that large water discharge during smolt migration correlates with a high return rate of adult salmon, presumably because of reduced predation pressure on the smolts. Results are also presented indicating poor feeding success of reared smolts compared to wild smolts, which may affect marine survival.

Anadromous brown trout and Atlantic salmon in the Aurland watercourse

The river Aurlandselva has been famous for its anadromous brown trout sport fishery, in particular because of the large size of the trout. Atlantic salmon has also been an attractive species. After the hydropower development, the catches of both species declined considerably, and harvesting of salmon has therefore been banned since 1989. This has taken place despite the hydropower company being enjoined to stock the river with 30 000 trout smolts and 10 000 salmon smolts annually. Because of low temperature and a short growth season the growth increment of presmolts is low, and mean smolt age and length of trout are 3.7 yrs and 142 mm, respectively, which is the same as the values before the hydropower development. The mean growth increment for the first summer at sea has declined, while the corresponding growth for the second and third summers at sea remains unaltered.

Biological characteristics of sea trout (Salmo trutta L.) smolts of known age from Osówka Stream

Biological characteristics of sea trout (Salmo trutta L.) smolts of known age from Osówka Stream

The mixing zone between limed and acidic river waters: complex aluminium chemistry and extreme toxicity for salmonids

When liming running waters, dosers must compensate for different flow and water qualities and for the downstream inflow from acid tributaries which creates mixing zones. At a certain point in the mixing zone, a constant or fluctuating chemical disequilibrium will appear due to transformation processes. In laboratory assays, over-saturated solutions of aluminium with ongoing active precipitation of aluminium have been found to be especially toxic to fish. Recent experiments in a mixing zone in the limed River Audna, Norway, have confirmed this phenomenon. Atlantic salmon ( Salmo salar L.) and sea trout ( Salmo trutta L.) smolts were exposed to acid and limed waters and mixtures of the two waters downstream from the point of connection. In the acid tributary (mean values: pH = 4·8, Ca = 1·3 mg litre −1, Al i = 236 μg litre −1), LT 50 was 22 and 40 h for Atlantic salmon and sea trout, respectively. In the mixing zone (pH = 4·8–6·5, Ca = 1·2–3·2 mg litre −1, Al i = 50–240 μg litre −1), LT 50 was 7 h for both species, masking the normal species difference in tolerance. Osmoregulatory failure and rapid gill lesions occurred in the mixing zone as an effect of the transformation of Al into high molecular weight precipitating species. This is the first documentation of the existence of such highly toxic mixing zones in nature, and the results clearly show that the mixing zone is even more toxic to fish than acid aluminium-rich waters.

Use of Electronic Fish Counters for Coho and Chinook Salmon, Steelhead, and Cutthroat Trout Smolts

Abstract Electronic fish counters produce accurate counts, are less stressful to fish, and require fewer personnel than traditional methods of counting smolts of coho salmon (Oncorhynchus kisutch), Chinook salmon (O. tshawytscha), steelhead (O. mykiss), and sea-run cutthroat trout (O. clarki) released from hatcheries.

Period of downstream migration of sea trout (Salmo trutta L.) smolts grown in Osówka Stream and their characteristics

Sea trout larvae were released in spring 1984 into the upper sector of Osówka Stream. Smolts of these fish were caught in three consecutive years after larvae release, in a fish trap placed in the middle course of the stream. The materials collected were used to determine period and water temperature at which smolts migrated downstream, as well as smolt length, weight and age composition.

Effects of river regulation on the structure of a fast‐growing brown trout (Salmo trutta L.) population

AbstractDuring the last 70 years, the Norwegian lake Mjøsa and its inflowing rivers have been subjected to serious changes due to hydroelectric power development. Regulation of the main inlet river, Gudbrandsdalslagen, started in 1919. The river power station at the Hunder fall was completed in 1964. This resulted in a reduction of winter water flow below the Hunder dam from approximately 26m3s−1 to 2m3s−1, which affected the most important spawning area of the fast‐growing population of brown trout, Salmo trutta L. The population was investigated in detail in 1907, 1909, 1961, and 1985, and river growth, smolt age, and growth in Lake Mjøsa are compared. Only wild fish were included in the study. The main pattern throughout this period shows an increased river growth rate before smoltification and reduced smolt age. The average smolt age dropped from 4.7 years in 1909 to 4.1 years in 1985, and at the same time smolt size decreased from 26.8 cm to 25.1 cm. Considering the major changes in abiotic factors in the river spawning section, the changes in age structure and growth of brown trout smolt are comparatively small.In Lake Mjøsa, increased productivity due to input of nutrients has obviously favoured forage fish such as smelt (Osmerus eperlanus (L.)) and vendace (Coregonus albula (L.)). The growth rate of brown trout in the lake has improved from 1909 to 1961 and 1985, followed by a reduced spawning age. However, due to increased human exploitation the average length of ascending fish (approximately 68 cm) and condition factor ( K = 1.14–1.16) have altered little.

Effect of Stocking Density on the Survival, Growth, and Dispersal of Steelhead Trout Fry (Salmo gairdneri)

In a coastal British Columbia stream a stocking density of between 0.3 and 0.7 fry/m2 maximized the production of steelhead trout (Salmo gairdneri) parr and smolts. A severe autumn flood doubled the mortality rates of fry stocked at densities of 0.7 fry/m2 or higher but had little effect on fry stocked at lower densities (<0.15 fry/m2). Overall survival to smolts appeared to be lower than measured elsewhere for wild fish (2 vs. 4.5 – 18%). The proportion (<10%) of surviving fry found below the stocked sections was considered to be an indicator of potential displacement mortality in streams with no vacant downstream areas. This downstream dispersal was not density dependent and was small in comparison with the mortality of nondispersing fish. Although initial fry and parr sizes were density dependent, there was no detectable density effect on older parr or smolt sizes.