Bacterial infections of Chinook salmon, Oncorhynchus tshawytscha (Walbaum), returning to gamete collecting weirs in Michigan

Herein, we describe the prevalence of bacterial infections in Chinook salmon, Oncorhynchus tshawytscha (Walbaum), returning to spawn in two tributaries within the Lake Michigan watershed. Ten bacterial genera, including Renibacterium, Aeromonas, Carnobacterium, Serratia, Proteus, Pseudomonas, Hafnia, Salmonella, Shewanella and Morganella, were detected in the kidneys of Chinook salmon (n = 480) using culture, serological and molecular analyses. Among these, Aeromonas salmonicida was detected at a prevalence of ～15%. Analyses revealed significant interactions between location/time of collection and gender for these infections, whereby overall infection prevalence increased greatly later in the spawning run and was significantly higher in females. Renibacterium salmoninarum was detected in fish kidneys at an overall prevalence of >25%. Logistic regression analyses revealed that R. salmoninarum prevalence differed significantly by location/time of collection and gender, with a higher likelihood of infection later in the spawning season and in females vs. males. Chi‐square analyses quantifying non‐independence of infection by multiple pathogens revealed a significant association between R. salmoninarum and motile aeromonad infections. Additionally, greater numbers of fish were found to be co‐infected by multiple bacterial species than would be expected by chance alone. The findings of this study suggest a potential synergism between bacteria infecting spawning Chinook salmon.     

Infections by Renibacterium salmoninarum and Nanophyetus salmincola Chapin are associated with reduced growth of juvenile Chinook salmon,Oncorhynchus tshawytscha (Walbaum), in the Northeast Pacific Ocean

We examined 1454 juvenile Chinook salmon, Oncorhynchus tshawytscha (Walbaum), captured in nearshore waters off the coasts of Washington and Oregon (USA) from 1999 to 2004 for infection by Renibacterium salmoninarum, Nanophyetus salmincola Chapin and skin metacercariae. The prevalence and intensities for each of these infections were established for both yearling and subyearling Chinook salmon. Two metrics of salmon growth, weight residuals and plasma levels of insulin-like growth factor-1, were determined for salmon infected with these pathogens/parasites, both individually and in combination, with uninfected fish used for comparison. Yearling Chinook salmon infected with R. salmoninarum had significantly reduced weight residuals. Chinook salmon infected with skin metacercariae alone did not have significantly reduced growth metrics. Dual infections were not associated with significantly more severe effects on the growth metrics than single infections; the number of triple infections was very low and precluded statistical comparison. Overall, these data suggest that infections by these organisms can be associated with reduced juvenile Chinook salmon growth. Because growth in the first year at sea has been linked to survival for some stocks of Chinook salmon, the infections may therefore play a role in regulating these populations in the Northeast Pacific Ocean.     

Bench‐top validation testing of selected immunological and molecular Renibacterium salmoninarum diagnostic assays by comparison with quantitative bacteriological culture

No gold standard assay exhibiting error‐free classification of results has been identified for detection of Renibacterium salmoninarum, the causative agent of salmonid bacterial kidney disease. Validation of diagnostic assays for R. salmoninarum has been hindered by its unique characteristics and biology, and difficulties in locating suitable populations of reference test animals. Infection status of fish in test populations is often unknown, and it is commonly assumed that the assay yielding the most positive results has the highest diagnostic accuracy, without consideration of misclassification of results. In this research, quantification of R. salmoninarum in samples by bacteriological culture provided a standardized measure of viable bacteria to evaluate analytical performance characteristics (sensitivity, specificity and repeatability) of non‐culture assays in three matrices (phosphate‐buffered saline, ovarian fluid and kidney tissue). Non‐culture assays included polyclonal enzyme‐linked immunosorbent assay (ELISA), direct smear fluorescent antibody technique (FAT), membrane‐filtration FAT, nested polymerase chain reaction (nested PCR) and three real‐time quantitative PCR assays. Injection challenge of specific pathogen‐free Chinook salmon, Oncorhynchus tshawytscha (Walbaum), with R. salmoninarum was used to estimate diagnostic sensitivity and specificity. Results did not identify a single assay demonstrating the highest analytical and diagnostic performance characteristics, but revealed strengths and weaknesses of each test.     

Estimating thermal exposure of adult summer steelhead and fall Chinook salmon migrating in a warm impounded river

Rising river temperatures in western North America have increased the vulnerability of many Pacific salmon (Oncorhynchus spp.) populations to lethal and sublethal risks. There is a growing need to predict and manage such risks, especially for populations whose life history or geography increases the likelihood of warm‐water exposure. We estimated thermal exposure of adult summer steelhead (O. mykiss) and fall‐run Chinook salmon (O. tshawytscha) as they migrated through a warm (often > 20 °C), 157‐km reach of the impounded Snake River, Washington. Archival temperature loggers and radiotelemetry were used to reconstruct thermal histories for 50 steelhead and 21 salmon. Encountered temperature maxima were mostly inside dam fishways and ranged from 15.8 to 24.0 °C (mean = 19.6 °C) for steelhead and from 18.0 to 21.6 °C (19.9 °C) for salmon. Behavioural thermoregulation was evident for ~50% of steelhead and ~30% of salmon in one of three reservoirs. Degree days (DDs) calculated from archival tags ranged from 74 to 973 DDs (median = 130) for steelhead and from 56 to 220 DDs (133) for salmon. Models using river temperature data and fish migration times accurately estimated total DDs for both species except some steelhead with extended thermoregulation. In a predictive application, we estimated exposure for 10,104 steelhead and 9071 Chinook salmon with passive integrated transponder‐tag detections at dams and found considerable DD variability across individuals, species and years. This estimation method, combined with baseline thermal surveys and existing monitoring infrastructure, can help to address long‐standing questions about how warm‐water exposure affects Snake River salmon and steelhead phenology, bioenergetics, physiology, survival and reproductive success.     

Purification and properties of digestive lipases from Chinook salmon (<Emphasis Type="Italic">Oncorhynchus tshawytscha</Emphasis>) and New Zealand hoki (<Emphasis Type="Italic">Macruronus novaezelandiae</Emphasis>)

Lipases were purified from delipidated pyloric ceca powder of two New Zealand-sourced fish, Chinook salmon (Oncorhynchus tshawytscha) and hoki (Macruronus novaezelandiae), by fractional precipitation with polyethylene glycol 1000, followed by affinity chromatography using cholate-Affi-Gel 102, and gel filtration on Sephacryl S-300 HR. For the first time, in-polyacrylamide gel activity of purified fish lipases against 4-methylumbelliferyl butyrate has been demonstrated. Calcium ions and sodium cholate were absolutely necessary both for lipase stability in the gel and for optimum activity against caprate and palmitate esters of p-nitrophenol. A single protein band was present in native polyacrylamide gels for both salmon and hoki final enzyme preparations. Under denaturing conditions, electrophoretic analysis revealed two bands of 79.6 and 54.9 kDa for salmon lipase. It is proposed that these bands correspond to an uncleaved and a final form of the enzyme. One band of 44.6 kDa was seen for hoki lipase. pI values of 5.8 ± 0.1 and 5.7 ± 0.1 were obtained for the two salmon lipase forms. The hoki lipase had a pI of 5.8 ± 0.1. Both lipases had the highest activity at 35°C, were thermally labile, had a pH optimum of 8–8.5, and were more acid stable compared to other fish lipases studied to date. Both enzymes were inhibited by the organophosphate paraoxon. Chinook salmon and hoki lipases showed good stability in several water-immiscible solvents. The enzymes had very similar amino acid composition to mammalian carboxyl ester lipases and one other fish digestive lipase. The salmon enzyme was an overall better catalyst based on its higher turnover number (3.7 ± 0.3 vs. 0.71 ± 0.05 s⁻¹ for the hoki enzyme) and lower activation energy (2.0 ± 0.4 vs. 7.6 ± 0.8 kcal/mol for the hoki enzyme) for the hydrolysis of p-nitrophenyl caprate. The salmon and hoki enzymes are homologous with mammalian carboxyl ester lipases.     

Influence of photoperiod and temperature manipulation on gonadal development and spawning in Caspian roach (Rutilus rutilus caspicus): Implications for artificial propagation

Caspian roach (Rutilus rutilus caspicus), a spring spawning teleost, were subjected to various photoperiod and temperature regimes to study the feasibility of shifting the timing of spawning for artificial propagation purposes. A total of 650 female reproductively mature R. rutilus caspicus were subjected to different photoperiod and temperature regimes including four light regimes (natural light (NL), 16 hr of light (L):8 hr of darkness (D), 9L:15D, 11L:13D), each affected by three temperature regimes (14, 20 and 24°C) for 70 days. Five fish per tank were randomly sampled on Feb. 10, Feb. 20, March 28, April 15 and April 30 (natural spawning time). Ovarian tissue sections were studied using light microscope and transmission electron microscope (TEM). The levels of 17‐β estradiol (E2) and 17α‐hydroxyprogesterone (OHP) were also measured in the serum samples. In late winter (March 28th), the gonadal maturation and spawning were accelerated in fish treated with the long day length (16L/8D) and warm temperature (20°C). While, the maturation of oocytes and spawning delayed in fish exposed to low temperature (14°C) and short day length (9L/15D and 11L/13D). Photoperiod seems to play a more important role in the ovarian development of the R. rutilus caspicus compared to temperature; since even among the fish treated with the lowest temperature (14°C), those exposed to a longer day length (16L/8D), matured and spawned earlier than the others. Considering that the earliest spawning occurred in R. rutilus caspicus treated with 16L/8D at 20°C and the latest spawning occurred in fish exposed to low temperature and short photoperiod, it can be concluded that temperature and photoperiod play an important role in accelerating oocyte maturation and spawning.     

Effects of rhythmic temperature change on the growth,body composition and energy budget of hybrid grouper (Epinephelus lanceolatus♂ × Epinephelus fuscoguttatus♀)

Effects of rhythmic temperature change on the growth, body composition and energy budget of hybrid grouper (Epinephelus lanceolatus ♂ × E. fuscoguttatus ♀) were investigated. Nine groups of fish received repeating cycles of low‐temperature manipulation (22°C) for 1, 2 and 4 days followed by recovery temperature (28°C) for (3, 7 and 11 days), (6, 14 and 22 days) and (12, 28 and 44 days) respectively, designated as L1R3, L1R7, L1R11, L2R6, L2R14, L2R22, L4R12, L4R28 and L4R44 respectively. In the control group (C), fish were reared at 28°C throughout the whole experiment. After 96‐day feeding trail, the final weight, relative weight gain rate, specific growth rate, food conversion efficiency and apparent digestibility coefficient of fish in L4R28 were significantly higher than those of control (p < .05). The crude protein contents of fish in L2R14, L2R22, L4R12, L4R28 and L4R44 were significantly higher compared to the control (p < .05). According to energy budget, fish in L4R28 exhibited significantly higher proportion of food energy assimilated into growth and lower proportion consumed for excretion than the control fish (p < .05). These results indicated the occurrence of complete or over growth compensation in hybrid grouper, and the use of repeated cycles of low temperature (22°C) for 4 days followed by recovery temperature (28°C) for 28 days could obtain enhanced growth, that is overcompensation, with improved apparent digestibility coefficient, food conversion efficiency and energetic efficiency into growth. This technique would be more practically applicable in indoor culture for this species.     

High‐throughput identification and quantification of Vagococcus salmoninarum by SYBR Green I‐based real‐time PCR combined with melting curve analysis

This work describes a primer pair and a high‐throughput SYBR Green I‐based real‐time PCR protocol combined with melting curve analysis for identification and quantification of Vagococcus salmoninarum in bacterial cultures and infected fish tissues. The 16S rRNA gene was selected for the design of the primer pair (SalF and SalR). The sensitivity and specificity of this primer pair were compared with other previously designed for conventional PCR. Although both primer pairs showed 100% specificity using pure bacterial cultures or DNA extracted from bacteria or fish tissues, the primer pairs designed in this study showed the highest sensitivity with a detection limit of 0.034 × 10⁰ amplicon copies per assay (equivalent to 2 × 10^?11 ng/µl, C_q value of 30.49 ± 1.71). The developed qPCR protocol allowed the detection of V. salmoninarum in non‐lethal and lethal fish samples with detection levels of 0.17 × 10⁰ gene copies in tissues artificially infected and 0.02 × 10⁰ in tissues of fish experimentally infected with V. salmoninarum. The high sensitivity of the developed method suggests that it could be considered as a useful tool for diagnosis of vagococcosis and the detection of V. salmoninarum in asymptomatic or carrier fish.     

Monitoring of the in-river migration of smolts from two groups of spring chinook salmon, Oncorhynchus tshawytscha (Walbaum), with different profiles of Renibacterium salmoninarum infection

Abstract Broodstock segregation based on the measurement of maternal Renibacterium salmoninarum infection levels by the enzyme-linked immunosorbent assay (ELISA) and the membrane filtration-fluorescent antibody technique (MF-FAT) was previously shown to affect the prevalence and levels of bacterial kidney disease (BKD) in progeny of chinook salmon, Oncorhynchus tshawytscha (Walbaum), during hatchery rearing. Subgroups of fish from that study were marked with passive integrated transponder (PIT) tags, and monitored by PIT-tag detectors during the first 342km of their migration to the Pacific Ocean. Differences in the recovery of tagged fish were significant (P≤ 0·01) at each detection point and became more pronounced as the fish moved downstream. Cumulative recoveries of fish from the low-BKD group and the high-BKD group, respectively, were 31% and 28% after 116km, 44% and 37% after 176km, and 51% and 42% after 342km. There were no apparent differences in the migration timing of the two groups to the first detection point. The data suggested that in-river survival was higher in the progeny group from parents that had low R. salmoninarum infection levels or tested negative for R. salmoninarum (low-BKD group) than in the group female parents with high infection levels (high-BKD group).     

Cultural characteristics of salmonid alphaviruses – influence of cell line and temperature

Laboratory studies were carried out to investigate the cultural characteristics of salmonid alphaviruses (SAV) from Atlantic salmon (AS, Salmo salar) and rainbow trout (RT, Oncorhynchus mykiss), particularly in relation to cell line and temperature. In an initial study, SAV was isolated from 12 viraemic sera and passaged in Chinook salmon embryo (CHSE‐214) cells at 15 °C. Geometric mean titres (GMT) after initial isolation were found to be significantly higher (P < 0.05) relative to those after two or four passages. Primary isolation of SAV was conducted from 12 viraemic sera (six AS and six RT) in seven different cell lines at 15 °C: CHSE‐214, rainbow trout gonad (RTG‐2), TO (derived from Atlantic salmon head kidney leucocytes), salmon head kidney (SHK‐1), blue fin‐2 (BF‐2), fat head minnow (FHM) and Epithelioma papulosum cyprini (EPC). Overall, significant differences were found between cell lines in both the numbers of strains where growth was detected and in the GMT obtained. For both AS and RT strains, GMT values were significantly (P < 0.01) higher in both TO and BF‐2 cells relative to the others, including CHSE‐214 and RTG‐2, the cell lines conventionally used for SAV. The effects of temperature of incubation (4, 10, 15 and 20 °C) on growth in TO, CHSE‐214 and RTG‐2 were investigated. In TO and RTG‐2 growth was optimal at 15 °C, whereas in CHSE‐214 results at 10 and 15 °C were more similar. Little or no growth was detected at 4 or 20 °C.     

Effects of temperature on amoebic gill disease development: Does it play a role?

A relationship between increasing water temperature and amoebic gill disease (AGD) prevalence in Atlantic salmon (Salmo salar) has been noted at fish farms in numerous countries. In Scotland (UK), temperatures above 12°C are considered to be an important risk factor for AGD outbreaks. Thus, the purpose of this study was to test for the presence of an association between temperature and variation in the severity of AGD in Atlantic salmon at 10 and 15°C. The results showed an association between temperature and variation in AGD severity in salmon from analysis of histopathology and Paramoeba perurans load, reflecting an earlier and stronger infection post‐amoebae exposure at the higher temperature. While no significant difference between the two temperature treatment groups was found in plasma cortisol levels, both glucose and lactate levels increased when gill pathology was evident at both temperatures. Expression analysis of immune‐ and stress‐related genes showed more modulation in gills than in head kidney, revealing an organ‐specific response and an interplay between temperature and infection. In conclusion, temperature may not only affect the host response, but perhaps also favour higher attachment/growth capacity of the amoebae as seen with the earlier and stronger P. perurans infection at 15°C.     

Spawning distribution and abundance of a northern Chinook salmon population

Chinook salmon, Oncorhynchus tshawytscha (Walbaum), is an important biological and cultural resource in Alaska, but knowledge about Chinook salmon ecology is limited in many regions. From 2009 to 2012, spawning distribution and abundance of a northern Chinook salmon population on the Togiak River in south‐west Alaska were assessed. Chinook salmon preferred deeper mainstem channel spawning habitat, with 12% (14 of 118 tags in 2009) to 21% (22 of 106 tags in 2012) of radio‐tagged fish spawning in smaller order tributaries. Tributary spawners tended to have earlier run timing than mainstem spawners. Chinook salmon exhibited extended holding and backout (entering freshwater but returning to saltwater before completing anadromous migration) behaviours near the mouth of Togiak River, potentially prolonging their exposure to fishery harvest. Mark–recapture total annual run estimates (2010–2012) ranged from 11 240 (2011) to 18 299 (2012) fish. Exploitation of Chinook salmon ranged from 36% (2012) to 55% (2011) during the study period, with incidental fishery catches near the mouth of the river comprising the largest source of harvest.     

Functional amino acids stimulate muscle development and improve fillet texture of Atlantic salmon

Sufficient firmness is essential for consumer appreciation and the suitability for processing of fish fillets. The objective of this study was to investigate the effect of functional amino acids (AA) on fillet texture and muscle development of Atlantic salmon. Triplicate net pens of 105 g salmon were fed a standard diet, or the same diet with added 15 g/kg arginine or 15 g/kg glutamate during a 5‐month rearing period. The growth rate and FCR (0.91–0.92) showed no significant dietary effects (body weight 864–887 g). Glutamate supplementation resulted in delayed postmortem glycogen degradation (pH drop) and rigour development, along with improved fillet firmness and intercellular myofibre integrity. An in vitro study with salmon myosatellite cells showed that exogenous glutamine or arginine increased the expression of muscle growth markers (myog, tnnl2, myl) at both 8 and 16°C culture temperature. The expression of a marker for proteolysis (ctsb), myl and myog were highest for the glutamine treatment at 16°C. Significant interaction between exogenous AA and temperature indicated elevated AA requirement when growth is accelerated. It is concluded that AA from the glutamate family are vital for fillet firmness. The dispensable glutamine and glutamate appear more critical compared to arginine, particularly during high‐performance periods.     

Vaccination of Atlantic lumpfish (Cyclopterus lumpus L.) at a low temperature leads to a low antibody response against Aeromonas salmonicida

We present a study on the effect of water temperature on immunization of Atlantic lumpfish. In total, 360 fish were vaccinated with either 50 μl of an oil‐based injection vaccine (VAX), with Aeromonas salmonicida and Vibrio salmonicida antigens, or PBS. Fish were vaccinated at three different water temperatures, 5°C, 10°C and 15°C, and sorted into six groups (N = 60). Lumpfish were weighed every 3 weeks after vaccination, sampled at 3, 6, 9 and 18 weeks post‐immunization (wpi) and evaluated by modified Speilberg score, ELISA and immunoblotting. Vaccinated fish showed low antibody response against V. salmonicida. Fish vaccinated at 5°C showed significantly lower antibody response against A. salmonicida throughout the study. At higher temperatures, vaccinated fish showed significantly increased antibody responses, at 18 wpi for 10°C and at 6 and 18 wpi for 15°C. Immunoblotting demonstrated specific response against the LPS antigen of A. salmonicida in the 10°C and 15°C VAX groups. Mean body weight increased in all groups throughout the study. Vaccinated fish had low Speilberg scores with no melanization of abdominal tissue. Our results show that vaccinating lumpfish at a lower water temperature may lead to a low antibody response against A. salmonicida.     

Live chilling of Atlantic salmon: physiological response to handling and temperature decrease on welfare

Investigation of the physiological effects of live chilling in Atlantic salmon, Salmo salar, has been performed in two experiments. In the first, fish (mean weight 840 g) acclimatized to either 16, 8, or 4°C were directly transferred horizontally or vertically (9 combinations) to water temperatures of 16, 8, 4, or 0°C using a dip net. Blood samples were collected at 1 and 6 h (h) post-transfer. In the second experiment, fish (mean weight 916 g) acclimatized to 16°C were exposed to four temperature-drop regimes (no physical handling): 16–4°C (over 5 h), 16–4°C (over 1 h), 16–0°C (over 5 h), and 16–0°C (over 1 h). Blood samples were collected 1 h post-temperature drop. Physical transfers in the first trial, i.e., temperature drops, resulted in immediate (1 h) increases in blood lactate concentrations at all three temperatures, but levels were significantly reduced and close to pre-transfer levels after 6 h. Horizontal transfers, i.e., 16–16°C, 8–8°C, and 4–4°C, resulted in similar increases and were not significantly different from the groups exposed to temperature drops. The most severe vertical transfer (16-0) resulted in a swift loss of equilibrium and eventually death. In experiment 2, temperature drops from 16 to 4°C and from 16 to 0°C over a period of one or 5 h, without physically handling the fish, resulted in no significant increases in any of the measured parameters 1 h post-transfer, except in the 16–0 (1 h) group. The latter experienced a significant increase in blood sodium, glucose, lactate, and cortisol levels compared to all other groups. The results suggest that salmon are capable of tolerating relatively steep temperature drops without any significant negative effects on blood stress parameters and that physical stress from handling overrides the effect of thermal insults.     

Stepwise temperature regulation and its effect on growth,feeding and muscle growth patterns of juvenile Atlantic halibut (<Emphasis Type="Italic">Hippoglossus hippoglossus</Emphasis> L.)

To investigate the possible direct effect of a stepwise reduction in temperature with increasing size on growth, feeding parameters and muscle growth patterns of juvenile Atlantic halibut (Hippoglossus hippoglossus L.), 804 juvenile halibut (mean initial weight individuals: 14.2 g ± 0.2 SEM) were reared at constant 9, 12 and 15°C or shifted (T-step, i.e. 15–12°C after 36 days) for 99 days. Despite indications of lower optimal temperature for growth with increasing size, equal end weights were obtained between the constant 12°C, constant 15°C and T-step groups. Best overall growth was observed for the group kept at constant 12°C. The limited effect of the T-step group may relate to the size at movement (too big), the temperatures investigated (close to optimum) and the time and size interval investigated (too narrow). Differences in growth were reflected more by alterations in feed intake (C _T and F%) than by differences in feed conversion efficiencies (FCE). Differences were found with respect to the density of muscle cells, whereas no differences were found between the average muscle cell diameters. The mean diameter of muscle cells tended to increase only slightly with increasing fish weight, while the mean density of muscle cells tended to decrease. Using an optimum temperature of 12°C, an indication of a possible increased rate of hyperplasia in relation to higher growth was seen.     

Effects of temperature on the growth of pollack (Pollachius pollachius) juveniles

Growth of juvenile pollack was assessed at five constant temperatures (9, 12, 15, 18 and 21 °C) in an 84-day trial. Duplicate groups of 75 fish (initial weight 143 ± 2 g) were held in O₂ saturated water (102–103% saturation) and fed to apparent satiation. Growth increased as temperature increased from 9 °C up to a plateau at 12–15 °C (NS differences between 12 and 15 °C) followed by a decrease from 18 °C. No growth occurred at 21 °C. For the overall period, specific growth rates were 0.52% and 0.53% day^− 1 at 12 and 15 °C compared to 0.40% day^− 1 at 18 °C. Feed intake was maximum at 15–18 °C (0.68–0.69% day^− 1) and it was significantly lower at 21 °C (0.45% day^− 1). Apparent feed conversion ratio was significantly higher at 18 °C than at 12–15 °C (1.8 compared to 1.2–1.4). There was no significant change in fish whole body composition related to temperature.At the end of the experiment, fish growth recovery following a transfer from 18 and 21 °C to 15 °C was assessed using a 50-day challenge test. Growth rate of the previous 21 °C group was the same as in the 15 °C group (NS differences) and in the previous 18 °C group it was significantly lower. The study showed that pollack have a high capacity to recover from a prolonged period of low or no growth induced by high temperatures.     

The prevalence of vertebral deformities is increased with higher egg incubation temperatures and triploidy in Atlantic salmon Salmo salar L.

Suboptimal egg incubation temperature is a risk factor for the development of skeletal deformities in teleosts. Triplicate diploid and triploid Atlantic salmon, Salmo salar L., egg batches were incubated at 6, 8 and 10 °C up until first feeding, whereupon fish were reared on a natural temperature before examination for externally visible skeletal deformities (jaw and spine) and radiographed for vertebral deformities and morphology at the parr stage. Increasing incubation temperatures and triploidy increased the number of fish showing one or more deformed vertebrae. Triploids had significantly higher mean vertebrae cranio‐caudal length (L) and dorsal‐ventral height (H) ratio at 6 and 10 °C than diploids, but triploidy had no effect on mean vertebrae centra area. Triploids demonstrated an increase in lower jaw deformities with increased incubation temperature, whereas jaw deformities were rare in diploids. Fish incubated at 10 °C had a significantly lower mean vertebral number than fish incubated at 6 °C, and triploids had lower mean vertebral numbers than diploids. Diploid fish with 58 vertebrae had a significantly higher mean vertebral centra area than fish with 59 vertebrae, but vertebral number did not affect the mean vertebral L/H ratio. The results are discussed with respect to the welfare and production of farmed salmonids.     

The effects of temperature on respiration of Amur sturgeon,Acipenser schrenckii,at two acclimation temperatures

In order to clarify the respiratory responses strategy of Amur sturgeon Acipenser schrenckii exposed to water temperature changes, respiratory parameters of the fish were studied under two temperature regimes: fish acclimated at 13°C for Group I, temperature was increased to 16°C, 19°C, 22°C and 25°C and then returned stepwise to 22°C, 19°C, 16°C and 13°C; and fish acclimated at 25°C for Group II, the water temperature was reduced in steps to 22°C, 19°C, 16°C and 13°C, subsequently, returned to 16°C, 19°C, 22°C and 25°C. The results showed that the respiratory frequency (f_R), oxygen consumption rate (VO₂) and gill ventilation (V_G) of the fish were directly dependent on the acute temperature in both acclimation groups (p < .05). The initial 25°C VO₂ in Group II was significantly higher than the initial 13°C VO₂ in Group I (p < .05), but was significantly lower than that at 25°C in Group I (p < .05). In Group I, respiratory stroke volume (V_S.R) of fish significantly increased or decreased with the acute temperature increases or decreases, respectively (p < .05); oxygen consumption efficiencies (EO₂) of fish did not significantly show differences when temperature increased to 25°C from 13°C (p > .05), but the EO₂ significantly declined while returning to acclimation temperature (p < .05). In Group II, the V_S.R of the fish did not significantly change with acute temperature fluctuations between 25 and 13°C (p > .05), while the EO₂ increased with acute temperature increases (p < .05). The Q₁₀ values for f_R, VO₂, V_S.R, V_G and EO₂ were 1.53–1.72, 1.92–2.06, 1.07–1.60, 1.78–2.44 and 1.11–1.65 at 13–25°C of temperature interval respectively. Amur sturgeon showed partial metabolic compensation to temperature changes. The study results suggest that the ability of Amur sturgeon to regulate metabolism in response to acute temperature changes makes this species good adaptability in the aquaculture rearing.