Evaluation of Fluorescent Pigment Marking of Brown Trout (Salmo trutta L.) and Atlantic Salmon (Salmo salar L.)

Fish farm and field trials have been conducted into the longevity and reliability of fluorescent pigment spray marking on brown trout and Atlantic salmon. These have shown that the technique produces high quality marks for a minimum of 20 months for brown trout and 7 months for Atlantic salmon. In addition a minimum size of 6.8 cm for the successful marking of brown trout fry has been established. High mortalities were found when the technique was used on fish which were subject to stress. Causes of stress are discussed and mortality rates of <1% have now been achieved.     

Effects of photoperiod, temperature and GnRHa treatment on the reproductive physiology of Atlantic salmon (Salmo salar L.) broodstock

The present study demonstrates that acceleratedphotoperiod advances ovulation in Atlantic salmon, and that exposure to cold water prior to spawning further advances and synchronizes this process while improving egg-survival. High water temperature inhibited both sperm release and ovulation, whereas a GnRHa treatment overrode this temperature effect in most individuals. A decrease in water temperature seemed to accelerate both ovulation and sperm release, and water temperature modulated the plasma 17,20βP profiles around ovulation and sperm release. The GnRHa treatment markedly increased the volume of strippable milt and the plasma 17,20βP levels in males.     

The effect of diet and environmental temperature on the faecal microbiota of farmed Tasmanian Atlantic Salmon (Salmo salar L.)

We investigated the changes in the faecal microbial population of the hindgut of farmed Atlantic salmon fed two commercial diets (A and B) over a 10‐month period. At each sampling round, hindgut contents of 40 fish (20 per diet) were pooled according to diet and cultivated on selective agar. The functional status of all microbiota was assessed against 48 substrates using the PhPlate generalized microplate, which also yielded a metabolic capacity (MC) value for each microbiota. Virulence gene profiles of each microbiota were also investigated. The number of different bacterial groups between two diets varied slightly and increased as water temperature peaked at 18.5°C during summer. This however, was associated with an increase in Vibrio numbers and a decrease in lactic acid bacterial numbers. A shift in the functional status of gut microbiota was observed as temperature increased, which was coupled with a decrease in the MC‐value of the microbiota in both diets. Of the 35 virulence genes tested from total DNA extract of the microbiota, only cdt and east1 were detected. Results indicate that temperature is the main driver of changes to the gut microbiota in farmed Tasmanian Atlantic salmon receiving these two diets.     

A comparison of aromatase inhibitors for the sex reversal of female Atlantic salmon (Salmo salar L.)

Immersion treatment of all female Atlantic salmon alevins with 1,4,6-androstatriene-3, 17-dione (ATD) (Steraloids Inc.) at doses of 0.5 and 5 mg l^?1 resulted in up to 54% masculinisation and fertility was the same as normal males.     

Atlantic Salmon (Salmo salar L.) in Brittany and Lower-Normandy: Preliminary Observations on the General Characteristics of Adults

This paper presents some characteristics (length, weight and age) of adult Atlantic salmon in rivers of Brittany. The data were derived from 1,578 fish caught mainly by rod and line; the remainder being from net catches in estuaries and small samples taken outside the fishing season. The bulk of the fish spent 1 or 2 years in freshwater before smoltifying. Those fish becoming smolts at the end of 1 year were the most numerous (54%). The majority of the fish sampled were spring fish (82.4%). Very few summer fish were identified and those found were mainly grilse. The high proportion of spring fish in the sample is due to the high proportion of rod-caught fish. Probably a complete census over the year would show a larger proportion of grilse and summer fish as these are not subject to heavy rod-fishing the season being closed at the beginning of June. The relationship between sea age and river age and the influence of freshwater life upon the sea life were tested in four rivers. It seems probable that sea life depends chiefly on the river and the year of smoltification rather than on the freshwater stage. The biometric characteristics of Brittany salmon were compared with data from some foreign rivers. The angling exploitation of the spring Atlantic salmon in Brittany and the lack of data about summer migrations are discussed in regard to the future of this stock.     

The progeny of sex-inverted female Atlantic salmon (Salmo salar L.)

A group of Atlantic salmon juveniles received dietary 17α-methyl-testosterone (3 mg/kg of food) for 60 days after first-feeding. Many of these fish became sexually mature as males at 1.5 years of age, while they remained in freshwater. Supposed sex-inverted females among these were identified by their failure to strip manually. Milt from the excised gonads of five of these fish was used separately to fertilise mixed ova from normal adult females. The progeny of each male, when examined 8 weeks after first-feeding, all had typically female gonads (n = 50).     

Mercury comparisons between farmed and wild Atlantic salmon (Salmo salar L.) and Atlantic cod (Gadus morhua L.)

Wild and farmed Atlantic salmon ( Salmo salar L.) and Atlantic cod ( Gadus morhua L.) were collected to assess changes in mercury with size in wild vs. farmed fish. Mercury concentrations were compared with Health Canada and United States Environmental Protection Agency consumption guidelines. Lipid dilution of mercury was examined by comparing lipid-extracted (LE) and non-lipid-extracted (NLE) flesh samples in both farmed and wild fish. Mercury concentrations in the flesh and liver of farmed salmon were significantly lower than concentrations in wild salmon of similar fork length ( P <0.001), possibly due to growth dilution in rapidly growing farmed fish. Mercury concentrations were higher in LE tissue compared with NLE ( P <0.05), suggesting lipid dilution of mercury in farmed fish with a high lipid content. Farmed cod, which do not grow more rapidly than wild cod, did not have significantly different flesh and liver concentrations compared with wild cod of similar fork length ( P >0.05). Between species of farmed fish, cod had significantly higher mercury concentrations than salmon ( P <0.05), but neither farmed nor wild salmon mercury concentrations exceeded federal consumption guidelines. These results suggest that rapid growth rates and a high lipid content may play important roles in regulating concentrations of contaminants such as mercury.     

Transport stress in Atlantic salmon (Salmo salar L.): anaesthesia and recovery

The effects of metomidate anaesthesia on levels of plasma cortisol, glucose, haematocrit and chloride in Atlantic salmon (1⁺) (Salmo salar L.), after a 2‐h transport and during a 48‐h recovery period were investigated. The use of metomidate anaesthesia during transport led to a reduced release of cortisol and significantly lower levels of plasma cortisol after a 48‐h recovery period. Plasma glucose did not return to basal level after a 48‐h recovery period, indicating that even longer recovery may be needed for the fish to return to a pre‐stress state. The results show that metomidate anaesthesia combined with a recovery period lessens the stress burden imposed by hauling and transport.     

Motoricity of Atlantic salmon embryos (Salmo salar L.) at different temperatures

Atlantic salmon eggs were fertilized and incubated in two temperature series at 3 and 8°C. Four motor criteria (heart rate, embryo motion, motion of the pectorals and motion of the mouth-gill apparatus) and oxygen consumption at different stages of embryogenesis were studied. At certain intervals the temperature was changed rapidly (within 30 min) to 3, 6, 8, 10, 12, 14 or 16°C and the detectable changes in the above motor criteria were recorded. Heart rate and embryo motion were the first recognizable motor components. The heart responded particularly sensitively to temperature shock with a change in heart rate, whereas temperature changes were not clearly reflected in embryo motion because space within the egg membrane was restricted owing to embryonal growth. Motion of the pectorals and mouth-gill apparatus did not start until shortly before hatching and achieved maximal values at 8–10°C. Pulse rates for all of the motor criteria except embryo motion were distinctly higher for eggs incubated at 8°C than for those incubated at 3°C.     

Gene expression responses to restricted feeding and extracted soybean meal in Atlantic salmon (Salmo salar L.)

We assessed effects of feed restriction and inclusion of 200 g kg^?1 extracted soybean meal in the diet on gene expression in Atlantic salmon using a cDNA microarray (SFA2.0) and real‐time qPCR. The trial lasted for 54 days. Restricted feeding and soybean inclusion reduced the thermal growth coefficient by respectively 51% and 22% compared with fish fed with the fishmeal‐based control diet to satiation. Soybean decreased distal intestinal expression of lysosomal (cathepsins C, D, L, Y and Z) and extracellular proteases while genes involved in responses to cellular stress were up‐regulated. Expression changes of immune genes suggested both pro‐ and anti‐inflammatory regulation. The hepatic responses to soybean and restricted feeding were highly similar, which could be because of negative effects of soybean meal on digestion and nutrient absorption. We observed up‐regulation of ribosomal proteins and down‐regulation of genes involved in lipid and steroid metabolism. Of note, growth reduction in both study groups was associated with coordinated down‐regulation of genes involved in oxidative and cellular stress responses, metabolism of xenobiotics and protein degradation. High expression of stress‐related genes in salmon fed with the control diet suggests that maximum growth rates can be associated with health problems.     

Evaluation of Sperm-Activating Solutions in Atlantic Salmon Salmo salar Fertilization Tests

The use of saline solutions was tested to determine their efficacy as replacements for ovarian fluid as sperm activators and to eliminate variability encountered with the use of Ovarian fluid. We tested fertilization rate of semen from eight males on Atlantic salmon Salmo salar eggs after five sperm-activating solutions and a non-activating saline were substituted for ovarian fluid. We used solutions shown acceptable for use with other salmonid species. The six solutions tested were a non sperm-activating phosphate-buffered saline (PBS, 7.2 g/L NaCl, 1.48 g/L Na₂HPO₄, 0.43 g/L K H₂PO₄), a Tris buffer (6.99 g/L NaCl, 3.63 g/L Tris and 2.42 g/L glycine), a Borax buffer (12.2 g boric acid/L in solution 1, 76 g disodium tetraborate/L combined 100:118, then 1 L combined with 3.7 L water and 18 g NaCl), and three solutions of 9.25 g/L (125 mM) NaCl buffered to pH 6.0, 7.5, and 8.9. The latter five solutions activated sperm immediately on contact, while PBS required additional water to activate sperm. The PBS solution was the least effective (mean percent eyed eggs 37.6%) for egg fertilization. The mean percent eyed eggs for the other five saline solutions (range 78% to 86%) were not significantly different. Sperm from one male provided significantly lower egg fertilization (39.6%) when compared with the other seven males (67.2–87.4% egg fertilization). Percent egg fertilization was not related to number of live sperm cells per egg. Our results show that osmotically-balanced sperm-activation solutions, even those with a pH range from 6.0 to 8.9 provide adequate media for fertilization of Atlantic salmon eggs. Fertilization in a deactivation saline and water reactivation of sperm resulted in low egg fertilization.     

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.     

Effect of low sea water temperature on water balance in the Atlantic salmon, (Salmo salar L.)

The water balance in Atlantic salmon (Salmo salar L.) overwintering in sea water (34 ) was investigated. With a decrease of temperature from 5.6 to 1.0°C the drinking rate decreased from 13.9 to 5.7 ml/kg/day, and the absolute amount of water absorbed decreased from 8.9 to 5.0 ml/kg/day. A decrease in temperature led, however, to an increase in the proportion of water absorbed in the intestines from 60 to 96%. Blood serum osmolarity increased from 320 to 440 mosm/1 with decreasing temperature and there was a reduction in tissue water content from 75 to 69% The disturbance of water balance at low temperature may be one of the factors responsible for mortality of salmon overwintering in sea water.