Impact of smolt production strategy on vertebral growth and mineralisation during smoltification and the early seawater phase in Atlantic salmon (Salmo salar, L.)

This study investigates the effect of different smolt production strategies on vertebral morphology (radiology), composition (mineral content) and mechanical strength (load-deformation testing) in Atlantic salmon (Salmo salar). Rapid-growing underyearling (0+) smolt were compared with slower-growing yearling (1+) smolt and a reference group of wild smolt (w). The underyearling and yearling smolt were transferred to seawater in October 2002 and May 2003, respectively. The underyearling smolt were reared under continuous light and the yearling smolt under natural light during the first twelve weeks in seawater, at ambient temperatures. Thus, the underyearling smolt hit seawater at 13 °C and were reared at 10-13 °C during the early seawater phase, whereas the yearling smolt hit seawater at 7 °C and were reared at 7-10 °C during the early seawater phase. All groups displayed increased longitudinal growth (up to 9% increase in relative length) of the caudal vertebrae during parr-smolt transformation. However, at transfer to seawater, the underyearling smolt had significantly lower vertebral mineral content (0+ 44%, 1+ 47%, w 50%) and higher incidence of deformed vertebrae (0+ 1.5%, 1+ 0%, w 0%), and at twelve weeks after transfer to seawater significantly lower vertebral mineral content (0+ 36%, 1+ 41%, w 43%), yield-load (0+ 6492 g, 1+ 8797 g, w 9150 g) and stiffness (0+ 7578 g/mm, 1+ 15,161 g/mm, w 20,523 g/mm), and significantly higher incidence of deformed vertebrae (0+ 2.5%, 1+ 0.3%, w 0%). There was a significant correlation between the mineral content and mechanical properties of the vertebrae. The underyearling smolt had significantly elevated plasma concentrations of total Ca, and P and Ca²⁺ during the parr-smolt transformation and in the early seawater phase.The results show that underyearling smolt may have an increased risk of developing vertebral deformities. It is possible that this risk can be reduced by postponing the start of the short-day treatment. This will reduce the temperature during smoltification, the temperature and daylength during the early seawater phase, and increase the age at smoltification.     

Effects of temperature and salinity on the course of infection with the haemoflagellate Cryptobia salmositica in juvenile Pacific salmon, Oncorhynchus spp.

Abstract. At 9°C juvenile sockeye salmon, Oncorhynchus nerka , inoculated intraperitoneally with 10⁵ Cryptobia (= Trypanoplasma ) salmositica began to succumb about day 15, with mortalities exceeding 90% by day 28. Fish inoculated at 8°C and acclimatized to 13°C began to die at about the same time but total mortalities were only about 75%. At 5°C the infection progressed more slowly, with the first mortalities occurring about day 25, but the disease seemed equally as lethal as at 9°C. All fish inoculated at 8°C and acclimatized to 20°C within 11 days survived the infection. Changes in salinity from fresh to sea water (30%o salinity) at 9°C or 13°C had almost no effect on the course of infection either when presmolts were slowly acclimatized to sea water over a period of 6-8 days or when smolts were transferred to sea water quickly (within 1-2 days). However, there were differences in susceptibility to disease among three species of salmon of smoking age. The order of decreasing sensitivity was chinook salmon, Oncorhynchus tshawytscha , with 100% mortality, sockeye salmon with 56 to 74% mortality and coho salmon, Oncorhynchus kisutch , with no mortality.     

Effects of photoperiod on gonadotropin-releasing hormone levels in the brain and pituitary of underyearling male barfin flounder

ABSTRACT:   A pleuronectiform fish, the barfin flounder Verasper moseri , expresses three gonadotropin-releasing hormone (GnRH) forms in the brain: salmon GnRH (sGnRH), chicken GnRH-II (cGnRH-II) and seabream GnRH (sbGnRH). To clarify the effects of photoperiod on GnRH systems, changes in brain and pituitary GnRH peptide levels were examined using time-resolved fluoroimmunoassays. In experiment 1, 5-month-old male barfin flounder (mean total length 9.0 cm, body weight 11.0 g) were divided into short (8:16 h light : dark [L:D] cycle; lights on 08.00–16.00 hours) and long photoperiod (16:8 h L:D cycle; lights on 04.00–20.00 hours) groups in mid September and maintained until November under natural water temperature (19.3–15.2°C). Brain sGnRH concentrations were significantly higher in the 16:8 h L:D group than in the 8:16 h L:D group, whereas no significant differences were observed in total length, body weight, plasma testosterone concentration, brain cGnRH-II concentration and pituitary sbGnRH content. In experiment 2, 7-month-old male barfin flounder (mean total length 16.5 cm, body weight 76.8 g) were divided into short and long photoperiod groups in mid December and maintained until February under natural water temperature (12.5–6.6°C). Total length, body weight and condition factor were significantly greater in the 16:8 h L:D group than in the 8:16 h L:D group, whereas no significant differences were observed in plasma testosterone concentration and GnRH levels in the brain and pituitary. These results indicate that levels of sGnRH in barfin flounder are influenced by photoperiodic treatment dependent on water temperature and/or body size.     

Soybean meal-induced enteritis in Atlantic salmon (Salmo salar L.) at different temperatures

This study evaluates the effect of temperature on the development of intestinal disorders when Atlantic salmon are fed soybean meal (SBM). In this study 20% of the dietary fishmeal was replaced by solvent-extracted Hipro SBM. Atlantic salmon reared at two different water temperatures (8 °C and 12 °C), were fed a control diet and an experimental diet for 20 days. Samples were taken at days 7 and 20. The extent of the morphological changes was assessed using a semi-quantitative scoring system developed for this purpose. The study demonstrates that enteritis is affected by temperature. The intestinal disorders were more severe in fish reared at 12 °C compared with those reared at 8 °C. It can be concluded from this study that temperature changes the speed but not the type of SBM-induced enteritis expressed as a delay on the response when Atlantic salmon are kept at lower temperatures.     

Seawater adaptation in atlantic salmon (Salmo salar L.) at different experimental temperatures and photoperiods

A study was made of the effect of gradually increasing day length at different temperatures on the smolting process and on growth of Atlantic salmon during smolting.The experiment consisted of ten experimental groups: a combination of three photoperiod- with three temperature-groups and a tenth control group.Size was found to be the most important factor in seawater adaptation of underyearling Atlantic salmon. Optimal growth in the experimental temperature and photoperiod regimes occurred at 15°C and at the photoperiod with the longest period of increasing day length.At the time for seaward migration, the most pronounced effect of photoperiod on seawater adaptation occurred at 11°C. At this temperature there was a significantly higher percentage of survivors at the photoperiod with the longest period of increasing day length.     

Perception of light intensity by Haliotis discus discus based on locomotor activity patterns

ABSTRACT:   An apparatus to measure the locomotor activity of aquatic benthic organisms at variable low light levels was developed and the diurnal behavioral pattern of the abalone Haliotis discus discus was measured at various low light intensities. During the experiment, abalone were exposed to 12 h light–dark cycles of complete darkness, 0 µmol/m²/s throughout the 12 h dark cycle and, during periods I (days 1–8) and III (days 19–26), the 12 h light cycles were set at 10 µmol/m²/s. During period II (days 10–17), abalone were exposed to a light level during the 12 h light cycles of 1 × 10⁻⁵, 1 × 10⁻⁶, 1 × 10⁻⁷ or 1 × 10⁻⁸ µmol/m²/s and the changes in locomotor activity assessed. At daytime levels of 1 × 10⁻⁵ µmol/m²/s, typical behavioral patterns were observed of high locomotory activity during the night-time cycle. However, at lower light intensities, the distinction between day and night activity patterns became less clear and, at intensities lower than 1 × 10⁻⁷ µmol/m²/s, the difference between activity during the light and dark cycles became negligible. Based on this, we conclude that the threshold of light level perception in relation to locomotor activity is approximately 1 × 10⁻⁷ µmol/m²/s. The significance of these results in relation to the entrainment of behavior in abalone is discussed.     

Effects of developmental stage, seawater concentration and rearing temperature on cryopreservation of Pacific oyster Crassostrea gigas larvae

ABSTRACT: For the development of a stepwise cryopreservation technique for larvae of the Pacific oyster Crassostrea gigas , various conditions were examined. Larvae at 9, 12, 15, 18 and 21 h after insemination were cooled at a rate of −1°C/min (seeding at −8°C for 15 min) and then plunged into liquid nitrogen at −35 or −40°C using 1.5 M dimethyl sulfoxide (DMSO) and 250 mM trehalose as cryoprotectants. Among these larvae, 15 h after insemination (the trochophore stage before formation of the shell gland) showed the highest motility and the best external appearance after thawing. Trochophore larvae were cryopreserved in preservation media containing different dilutions (1/4, 1/6, 1/8, 1/10 and 1/30) of seawater. Larvae preserved in the 1/4 seawater medium showed the highest appearance of shelled larvae 4 days after thawing. Trochophore larvae reared in seawater at 21, 25 or 29°C were cryopreserved for 8 months and then reared at 26°C after thawing. Larvae reared at 25°C showed the highest survival rate and normal larval ratio at day 6 after thawing, although larvae reared at 21°C showed the highest rates until day 4. One larva developed at 25°C succeeded to settle.     

Interactions of temperature,size and photoperiod on growth and smoltification of chinook salmon (Oncorhynchus tshawytscha)

Underyearling fall chinook salmon (Oncorhynchus tshawytscha) were reared at two temperatures (9 and 15°C) and three photoperiods simulating winter (WIN), spring—summer (SS), and natural (NAT) conditions. The two artificial photoperiods were adjusted according to fish size so that an equinoctial photoperiod was synchronized with a hypothesized optimum size range for smolting (8–14 cm fork length). Fish exposed to a winter (WIN) photoperiod had the slowest growth rate. Fish under the SS photoperiod at both temperatures and under the WIN photoperiod at 9°C displayed hypoosmoregulatory capability near the equinoctial daylength. Thyroxine concentrations in fish reared under a natural photoperiod remained at basal levels during the period of early saltwater adaptiveness and throughout the remainder of the experiment. Thyroxine titers showed significant increases under all experimental photoperiod—temperature combinations near the equinoctial daylength with the exception of the 15°C/SS treatment.     

Effect of different photoperiod cycles on metabolic rate and energy loss of fed and unfed adult tilapia Oreochromis niloticus: Part II

ABSTRACT: To study the influence of different photoperiod cycles on the metabolic rate and energy loss of fed and unfed adult tilapia Oreochromis niloticus (bodyweight 102–107 g) at 28°C, four photoperiod cycles (i.e. 3L : 3D, 6L : 6D, 12L : 12D, and 24L : 24D) were applied. A computer-operated respirometer with a closed tank was used so as to prevent water from condensing from the air or evaporating into the air. A photoperiod-mediated metabolic cycle was demonstrated during the routine state in which the metabolic rate was higher during the light phase compared with during the dark phase for all photoperiods. The combined effects of photoperiod and feeding episodes acted as a strong Zeitgeber (cue or synchronizer) for synchronizing the daily rhythm in fed fish. Fish exposed to short photoperiod cycles showed a higher metabolic rate and energy loss compared with those exposed to longer photoperiod cycles. Mean oxygen consumption in the fed and unfed fish were 295.7 mg/kg per h and 149.8 mg/kg per h, respectively, during the 3L : 3D period; 286.5 mg/kg per h and 143.3 mg/kg per h during the 6L : 6D period; 262.2 mg/kg per h and 130.3 mg/kg per h during the 12L : 12D period; and 238.3 mg/kg per h and 120.4 mg/kg per h during the 24L : 24D period. The highest post-prandial increase in energy loss was recorded during the 3L : 3D period (56.2 kJ/kg per day), followed by 55.1 kJ/kg per day during the 6L : 6D period, 50.7 kJ/kg per day during the 12L : 12D period, and 45.4 kJ/kg per day during the 24L : 24D period. The study's results demonstrated that the fish conserve energy when raised under longer photoperiod cycles.     

Changes in GnRH levels in the brain and pituitary gland during migrations of sockeye salmon and chum salmon

Levels of two moleculer types of gonadotropin-releasing hormone (GnRH), salmon GnRH (sGnRH) and chicken GnRH–II (cGnRH–II) in the various brain regions and pituitary gland of sockeye salmon (Oncorhynchus nerka) and chum salmon (O. keta) during smoltification and spawning migration, respectively, were measured using specific time-resolved fluoroimmunoassay (TR-FIA) systems. Changes in sGnRH levels in different brain regions tended to be specifically synchronized with serum thyroid hormone or pituitary gonadotropin (GTH) levels during smoltification and spawning migration, respectively. In contrast, cGnRH–II levels did not show such synchronized changes. SGnRH and cGnRH–II in various brain regions might have different roles during smoltification and spawning migration of salmonid fishes.     

Growth and sexual maturation in Atlantic salmon, Salmon, salar L., reared in sea cages at two different light regimes

Abstract. Immature 1-sea-winter (ISW) Atlantic salmon, Salmo salar L. were reared in sea cages under natural light or constant additional light from 15 October 1987 to 24 June 1988 when the fish were fin clipped according to photoperiod and reared in a common cage under natural photoperiod until maturation. The group subjected to constant additional light (LL) had an overall increase in growth rate, which indicates a seasonal growth pattern influenced by photoperiod. An advanced ovulation time in the LL group gives further support to the hypothesis that endogenous rhythms controlling growth rate have been influenced. Incidence of maturation was lowest in the LL group.     

Temperature-mediated en route migration mortality and travel rates of endangered Snake River sockeye salmon

Abstract  Conservation efforts for endangered Snake River sockeye salmon ( Oncorhynchus nerka ) have been hindered by high en route adult mortality during their ∼1450 km freshwater spawning migration. Identifying causal factors for this mortality has been difficult given very small (often <10 fish) annual returns in recent decades. However, several hundred hatchery-bred fish returned in 2000 and we intercepted and radio-tagged 31 in mid-migration to monitor behaviours and survival. All fish initially migrated at similar rates, but later-timed fish eventually slowed migration and were far more likely to be unsuccessful. Late-season mortality was strongly associated with water temperatures near tolerance thresholds (21–24 °C). The data also suggest increased risk for fish in poor initial condition (i.e., with injuries or parasites) and probable recent selection against late-timed salmon. Results parallel temperature- and condition-related adult mortality in Columbia and Fraser River sockeye salmon populations and demonstrate the potential vulnerability of marginal southern populations to regional climate warming.     

Serum thyroxine,estradiol-17β, and testosterone profiles during the parr-smolt transformation of masu salmon,Oncorhynchus masou

Changes in serum thyroxine (T₄), estradiol-17β (E₂) and testosterone (T) levels during the parr-smolt transformation (smoltification) were investigated in the masu salmon (Oncorhynchus masou) in 1985 and 1987. T₄ showed a peak in levels at the early stage of smoltification and E₂ and T levels peaked almost at the same time. There were no significant differences between the concentrations of serum hormones in female and males. During smoltification, germ cells in the peri-nucleolus and spermatogonia stage were present in the ovary and testis, respectively. These results suggest that E₂ and T may be involved in smoltification in the masu salmon.     

Plasma somatolactin levels in coho salmon (Oncorhynchus kisutch) during smoltification and sexual maturation

Somatolactin (SL) is a novel pituitary hormone recently characterized in several fish species. Structural analyses have shown that SL belongs to the growth hormone/prolactin family, and that it is a highly conserved protein. SL is synthesized by the periodic acid/Schiff-positive cells in the pars intermedia, but has an as yet unidentified function(s). We have recently developed a homologous radioimmunoassay for coho salmon SL and measured plasma levels of SL during two stages of the coho salmon life cycle, smoltification and sexual maturation. During smoltification, plasma levels of SL changed almost in parallel with plasma levels of thyroxine; levels increased as morphological indices of smoltification appeared and decreased as smoltification was completed. Following this period, SL levels remained low until the spring prior to spawning. In a separate study, plasma levels of SL were measured in sexually maturing coho salmon that remained in fresh water throughout their life cycle. During the year of sexual maturation, plasma levels of SL gradually increased from the spring onward, reaching peak levels at the time of spawning in November and December. These data are similar to those previously reported for sexually maturing coho salmon that were maintained in seawater prior to spawning (Rand-Weaver et al. 1992). Therefore, increases in plasma SL levels occurred in sexually maturing fish irrespective of whether they were maintained in fresh water or seawater. Peak levels at spawning were higher than those observed during smoltification. Possible roles for SL in metabolism and reproduction are discussed.     

Water temperature and dietary histidine affect cataract formation in Atlantic salmon (Salmo salar L.) diploid and triploid yearling smolt

The aim of the present study was to investigate cataract development in diploid (2N) and triploid (3N) Atlantic salmon smolts and post‐smolts at two water temperatures (10 and 16 °C) given diets with different histidine supplementation (LH, 10.4 and HH, 13.1 g kg^?1) before and after seawater transfer. In freshwater, a severe cataract outbreak was recorded in both ploidies reared at 16 °C. The cataract score was significantly higher in triploids compared to diploids, and the severity was lower in both ploidies fed the HH diet. The cataract development at 10 °C was minor. Low gill Na⁺, K⁺‐ATPase activity in fish reared at 16 °C before seawater transfer was followed by osmoregulatory stress with elevated plasma electrolyte concentrations and high mortality in sea water. Both diploids and triploids reared at 10 °C developed cataracts during the seawater period, with higher severities in triploids than diploids and a reduced severity in the fish fed the HH diet. The findings of this study demonstrate the importance of environmental conditions in the husbandry of Atlantic salmon, and particularly triploids, with regard to smoltification and adjusted diets to mitigate cataract development in fresh and sea water.     

Diel timing of molting and metamorphosis of Panulirus japonicus phyllosoma larvae under laboratory conditions

ABSTRACT:   The timing of molting and metamorphosis was monitored for Panulirus japonicus phyllosoma larvae cultured in the laboratory. Larvae cultured under natural light–dark cycle molted synchronously within approximately 1.0 h before and after sunrise, except for a short period after hatching; the timing of molting changed with time of sunrise. When three artificial light–dark cycles were introduced, larvae molted around the start of lighting, irrespective of the light–dark cycles. In the event of a sudden change in the start or end of lighting, molting was regulated by an endogenous rhythm. The start of lighting had a greater impact on the timing of molting than the end of lighting, suggesting that sunrise is probably the critical signal for phase-setting in molting rhythm. Metamorphosis to the puerulus stage occurred within 0.4 h before and 1.2 h after sunset under a natural light–dark cycle, and the timing of metamorphosis was also changed artificially by regulating the end of lighting.     

Behaviour and thermal experience of adult sockeye salmon migrating through stratified lakes near spawning grounds: the roles of reproductive and energetic states

Roscoe DW, Hinch SG, Cooke SJ, Patterson DA. Behaviour and thermal experience of adult sockeye salmon migrating through stratified lakes near spawning grounds: the roles of reproductive and energetic states. Ecology of Freshwater Fish 2010: 19: 51–62. © 2009 John Wiley & Sons A/S
Abstract –  Little is known about physiological factors underlying thermal behaviour in Pacific salmon ( Oncorhynchus spp.). We implanted acoustic transmitters and temperature loggers into migrating adult sockeye salmon ( Oncorhynchus nerka ) and nonlethally assessed their reproductive hormone levels and energetic states immediately prior to their passing through natal lakes en route to spawning grounds. We tested the hypothesis that energetic and reproductive status influence thermoregulatory and other in-lake behaviours. More reproductively advanced females with lower levels of energy transited through cooler temperatures compared to less mature females with high levels of energy, possibly to reduce metabolic energy expenditure and delay final maturation. Transit temperatures of males were not related to physiological variables. Salmon travelled on average 13.6 km·day⁻¹ through two lakes, and often circled or held for more than 1 day before moving upstream, but these behaviours were generally not related to physiological variables.     

Spatial correlation patterns in coastal environmental variables and survival rates of salmon in the north-east Pacific Ocean

We examined spatial correlations for three coastal variables [upwelling index, sea surface temperature (SST), and sea surface salinity (SSS)] that might affect juvenile salmon ( Oncorhynchus spp.) during their early marine life. Observed correlation patterns in environmental variables were compared with those in survival rates of pink ( O. gorbuscha ), chum ( O. keta ), and sockeye ( O. nerka ) salmon stocks to help identify appropriate variables to include in models of salmon productivity. Both the upwelling index and coastal SST were characterized by strong positive correlations at short distances, which declined slowly with distance in the winter months, but much more rapidly in the summer. The SSS had much weaker and more variable correlations at all distances throughout the year. The distance at which stations were no longer correlated (spatial decorrelation scale) was largest for the upwelling index (> 1000 km), intermediate for SST (400–800 km in summer), and shortest for SSS (< 400 km). Survival rate indices of salmon showed moderate positive correlations among adjacent stocks that decreased to zero at larger distances. Spatial decorrelation scales ranged from approximately 500 km for sockeye salmon to approximately 1000 km for chum salmon. We conclude that variability in the coastal marine environment during summer, as well as variability in salmon survival rates, are dominated by regional scale variability of several hundred to 1000 km. The correlation scale for SST in the summer most closely matched the observed correlation scales for survival rates of salmon, suggesting that regional-scale variations in coastal SST can help explain the observed regional-scale covariation in survival rates among salmon stocks.     

Ovarian development and induced oviposition of the overwintering swimming crab Portunus trituberculatus (Brachyura: Portunidae) reared in the laboratory

ABSTRACT:   Females of the swimming crab Portunus trituberculatus were cultured under natural temperature and high temperature (21°C) conditions to examine ovarian development and oviposition from autumn (October) to the beginning of breeding season in the following spring (May). Ovaries developed because of vitellogenesis of oocytes from October to December and their developmental state did not change during the overwintering period from December to March. In spring, from late March to mid May, some ovaries reached prematuration and maturation stages and ovipositions began from mid–late April under natural temperature conditions. Females reared in tanks of high temperature regimes oviposited earlier than those reared in tanks of natural temperatures. The number of days to oviposition tended to decrease with advancement of the beginning times (early February to late April) of culture of females under high temperature regimes; induced ovipositions were achieved more easily with increasing photoperiod from c . 12 h in early February to c . 14 h in late April. Therefore, it is inferred that the temperature and photoperiod are important environmental factors controlling ovarian development and oviposition.     

Effects of copper on survival and growth of larval false clown anemonefish <Emphasis Type="Italic">Amphiprion ocellaris</Emphasis>

ABSTRACT:   Larval false clown anemonefish of about 12 h after hatching were fed newly-hatched brine shrimp nauplii in natural (control) and copper-added seawater (40–640 µg–Cu/L) at 26.5 ± 0.5°C for 14 days. Survival rate of the fish increased with increasing copper concentrations up to 160 µg–Cu/L. The rates at 80 and 160 µg–Cu/L were 65 and 80%, respectively, and were significantly higher than that of the control (30%). A positive effect of copper addition on the survival rate was also observed in the other rearing experiment with the fish from seven different spawning chances. Growth rate of the survival fish was not affected by copper concentrations. The copper concentration of the survived fish increased with increasing copper concentrations in the rearing water.