Added value from an added chromosome: Potential of producing large fillet fish from autumn to spring with triploid rainbow trout,Oncorhynchus mykiss

Three‐summers‐old all‐female triploid and diploid rainbow trout were compared after one on‐growing season in sea net cages. Slaughter traits of round weight, gutted weight, fillet weight, carcass% and fillet% were measured at three times in November 2017, January and April 2018. The triploid group had lower daily growth coefficient mean (4.25) and higher feed conversion ratio (1.18) than diploids (4.48 and 1.05, respectively) during on‐growing (June–November). In November, no difference of means was found between mature or immature diploids and triploids for any of the weight traits when the effect of vertebrae defects was statistically removed. However, the triploids had attained higher means than mature or immature diploids in gutted and fillet weight by January, suggesting that the loss of muscle mass during early winter was lower in triploids. Sexually maturing diploids (46%) had lower slaughter yield means compared to triploids or immature diploids at each measurement time, and these differences also increased during overwintering. Instead, the means of yield traits remained similar between the triploid and immature diploid groups through the winter. Likewise, fillet redness remained at equally high level in triploids and immature diploids, whereas in maturing diploids this attribute decreased substantially during overwintering. The triploid group had a higher incidence of vertebral defects (12.0%) than diploids (5.3%). The present results demonstrate the potential of triploid trout in producing large‐sized (>2 kg) fillet fish until spring markets. However, more detailed investigations are needed, particularly regarding the animal health and growth efficiency in triploids, relative to their diploid counterparts.     

Effects of triploidy on feed efficiency, morphometric indexes and chemical composition of shi drum, Umbrina cirrosa L.

Productive performances of triploid (3n) and diploid (2n) shi drum (Umbrina cirrosa L.) were evaluated over an experimental period of 76 days. Fish, selected according to body weight (196 specimens from each ploidy), were reared in tanks (two for each thesis) under the same environmental and dietary conditions. A practical extruded diet (crude protein: 43.4%; ether extract: 19.3%) was offered to fish according to a feeding rate that varied from 1% to 1.5% of live weight. Both at the beginning and at the end of the trials, samples of fish were submitted to morphometrics and chemical analysis. The final body weight and the specific growth rate of triploid fish were significantly lower than those of fish diploid. The feed efficiency of triploids showed a reduction in crude protein retention. Juvenile triploids evidenced a larger amount of coelomatic fat, and their gonads were atrophic. The whole‐body proximate composition of 3n fish was characterized by a higher ether extract and a lower crude protein content than 2n fish. Triploids had higher liver lipid content; there were no significant differences in viscera proximate composition. Sum, the results showed that chromosome set manipulation in this species can reduce productive performances at a juvenile stage, influencing some morphometric traits.     

Colour measurement, using the CIELCH colour space, of muscle of rainbow trout, Oncorhynchus mykiss (Walbaum), fed astaxanthin: effects of family, ploidy, sex, and location of reading

Thirty two families (representing 397 fish of 900 g average weight) of rainbow trout. Oncorhynchus mykiss (Walbaum) (16 diploid sib-groups and their homologous triploids obtained by heat shock) were fed astaxanthin (96 mg kg^-1 feed) for 39 days, resulting in a red colouring of the muscle. The colour was measured in the CIELCH colour space using a chromameter at three points of fish muscle (head, middle and tail). The effects of ploidy, sex, family and location of measurement on the colour attributes offish muscle (lightness, chroma and hue angle) were analysed. Diploid fish had a higher chroma than triploid ones (P<0.02), but no ploidy effect was found on lightness nor on hue angle. Sex had little influence on colour attributes, except for the hue angle which was slightly higher (P<0.07) in females than in males. Family had a strong effect on chroma (P<0.002), hue angle (P<0.02), and, to a lesser extent, on lightness (P<0.07). However, within families the muscle colour was very variable from one fish to another (highly significant variation [P<0.0001] on every colour attribute). The location effect was highly significant on lightness (P<0.0001), chroma (P<0.0001), and hue angle (P<0.0001). Data from the tail part of the fish muscle were higher than those from the head part. The middle part always exhibited the lowest data.     

Flesh characteristics: estimation of genetic parameters and correlated responses to selection for growth rate in the GIFT strain

Flesh characteristics comprising chemical composition (protein, fat and moisture percentages and pH) as well as a sensory attribute (colour) were measured in 1951 fillet samples from two generations of two populations (a selection line, selected for increased harvest weight, and a control line, selected for average breeding values for harvest weight) of the genetically improved farmed tilapia (GIFT) strain of Nile tilapia. These data were jointly analysed with 5331 harvest weight records from three generations to estimate genetic parameters and correlated selection responses. Multiple trait animal models were used in the analyses. The potential for correlated responses was evaluated by estimating heritabilities and genetic correlations between body traits (weight, length, depth and width) and fillet traits (weight and yield) with the above mentioned flesh characteristics. The heritabilities for protein%, fat% and colour were low (0.06–0.11), whereas for moisture% and pH they were moderate (0.15–0.20). Genetic correlations among some flesh characteristics (moisture% with protein%, fat% and pH and with fat%) as well as between body and fillet traits with flesh characteristics, were significantly different from zero but low (?0.34 to 0.31). Correlated responses were evaluated by comparing the least squares means between the Selection and Control lines. Our results indicate that selection for high growth increased harvest weight in the Selection line relative to the Control line but it did not change the flesh characteristics of the GIFT strain.     

Effect of ploidy on the mortality of Crassostrea gigas spat caused by OsHV‐1 in France using unselected and selected OsHV‐1 resistant oysters

The effect of ploidy on the mortality of Crassostrea gigas spat caused by the ostreid herpesvirus (OsHV‐1) genotype μVar was investigated at five sites along the Atlantic coast in France in 2011. Sibling diploids and triploids were produced using either unselected or selected OsHV‐1‐resistant oysters. No significant interactions were found between the factors of environment, genotype and ploidy at the endpoint dates. The mean mortality rates at the sites were 62% and 59% for diploids and triploids, respectively, and the two rates were not significantly different. The mean mortality rates were 33% and 32% for sibling diploids and triploids, respectively, when OsHV‐1‐resistant parents were used and 91% and 85%, respectively, when unselected parents were used. The results were confirmed through other broodstocks tested in 2013. Our study is the first to clearly show that mortality related to OsHV‐1 is similar between diploids and triploids in C. gigas when the same germplasm is used for both ploidy. Furthermore, OsHV‐1 resistance was not substantially altered by triploidization, indicating that the achieved selective breeding of diploid oysters for OsHV‐1 resistance can be translated into improved survival in triploids.     

Muscle growth of triploid Atlantic cod juveniles (Gadus morhua)

This study has investigated the muscle growth of diploid and triploid Atlantic cod (Gadus morhua) juveniles raised in replicate tanks over a period of 29 weeks and analysed at three sampling points (February, June and September). Data for weight, length, condition factor (K), muscle fibre growth and myogenic progenitor cells (MPCs) number were collected and results were analysed in relation to body growth and ploidy status. Diploids were significantly heavier than triploids throughout the trial (~10–20%) and had K in June and September samplings. Over the whole period, the rate of muscle fibres' recruitment was 318 fibres per day and 252 fibres per day for diploid and triploid cod respectively. The larger body weight of diploids resulted in a total number of fast fibre number of 114 979 compared to 91 086 in triploids. The average diameter of the 2.5% of the smallest fibres (2.5th percentile) was higher in diploids than triploids at the start of the trial, with a reversed picture for the average of the upper 2.5% (97.5th percentile) at the end of the trial. The probability density function of the estimated muscle fibre diameters showed similar fibre size distribution between size‐matched diploids and triploids at all sample points. The peak fibre diameter was approximately 25 μm in February and increased to approximately 50 μm in June and September, irrespectively of ploidy. Pax 7 were used as molecular markers for MPCs. A positive correlation between Pax 7⁺ cells and total body length was observed only among triploid fish at the onset of the experiment.     

Comparative Growth of Diploid and Triploid Asian Catfish Clarias macrocephalus in Thailand

Wild caught Asian catfish were spawned manually following HCG injection, and a portion of the eggs were subjected to cold-shock at 4 C for 15 min within 2-min post-fertilization. Nuclear diameter measurements of cold-shocked fish revealed that 96% were triploids (3N), while non-shocked fish were all diploids (2N). During larval and fry culture (first 26 d), triploid fish mortality was =50%, while diploid mortality was =25%. Following 8-mo culture in tanks at three stocking densities, triploid fish survival was significantly greater ( P < 0.05), than diploids, with 84.0% and 57.3%, respectively. Triploid live weight was also significantly greater than diploids, with 69.2 and 45.9 g averages, respectively. Ninety-two percent of diploids had welldeveloped gonads after 8 mo; whereas none of the triploids had mature gonads. Gonads were undifferentiated with 31% of the triploids. These sexually undifferentiated fish had greater growth rates than male or female triploids, and greater growth than all diploids. Carcass weight (gutted) of triploids was 95.8% of live weight, compared with 92.5% for diploids. Lastly, triploids had very few deformities compared with diploids, with 1.3% and 17.6%, respectively. Deformities included curved spines, and humped backs just posterior of the head.     

Quality Characteristics of Fresh Rainbow Trout as Perceived by the Danish Processing Industry

The views of Danish processors were sought in an attempt to identify criteria considered important for fresh pan-sized rainbow trout Onchorhynchus mykiss. Principle component regression (PCR) analysis, carried out on the survey data revealed that two components accounted for 55% of the parameter variance. The first component, describing morphometric characteristics, explained 33% of variance and the second, describing skin appearance, explained 22% of the variance. A significant correlation (P < 0.001) was obtained between fillet colour and fillet colour appeal, with preference for white flesh in fish fed unpigmented feed.     

Preslaughter stress and subsequent effect on flesh quality in farmed cod

The aim of this study was to investigate the effect of prehandling stress on the flesh quality of Atlantic cod (Gadus morhua). In order to stress the animal, water was reduced in the tank before a total of 30 fish were caught five at a time using a dipnet and held for 3 min, causing stress by hypoxia. This fish was compared with a control group (n=30) of fish exposed to anaesthetics directly in the tank. All fish were killed by a percussive blow to the head and exsanguinated and stored on ice before flesh quality was measured. Immediately after death and after ice storage for 3 and 8 days, 10 fish per group were measured for muscle pH, texture, fillet gaping, colour, drip loss and cathepsin D. Handling stress resulted in an initial increased fillet lightness, drip loss and decreased fillet shear force, although these differences did level off during ice storage. Stress caused by handling resulted in earlier onset of rigour mortis as compared with the control group, which reached maximum rigour tensions within 26 and 36 h postmortem respectively. We conclude that handling before harvest results in reduced time before entering rigour. After 8 days of ice storage, no effect of handling stress was seen on the muscle pH, flesh colour, fillet shear force, gaping score, drip loss or cathepsin D activity.     

Effects of temperature on feed intake and plasma chemistry after exhaustive exercise in triploid brown trout (<Emphasis Type="Italic">Salmo trutta</Emphasis> L)

The physiological effect of temperature on feed intake and haematological parameters after exhaustive swimming in diploid and triploid brown trout (Salmo trutta) was investigated. Trout were exposed to an incremental temperature challenge (2 °C/day) from ambient (6 °C) to either 10 or 19 °C. Feed intake profiles did not differ between ploidy at 10 °C; however, triploids had a significantly higher total feed intake at 19 °C. After 24 days, each temperature–ploidy group was exposed to exhaustive swimming for 10 min. The haematological response differed between ploidy, with the magnitude of the response affected by temperature and ploidy. Post-exercise, acid–base and ionic differences were observed. Plasma lactate increased significantly from rest for both temperature and ploidy groups, but glucose increased significantly at higher temperature. Post-exercise, triploids at 19 °C had significantly higher osmolality and cholesterol than diploids, but differences were resumed within 4 h. Elevated alkaline phosphatase (ALP) and aspartate aminotransferase (AST) in fish at higher temperature suggested greater tissue damage; however, both ploidy responded similarly. Despite no significant differences in deformity prevalence, the type and location of deformities observed differed between ploidy (decreased intervertebral space with higher prevalence in tail area and fin regions for diploids, while vertebral compression, fusion in cranial and caudal trunks for triploids). These results suggest triploids have greater appetite than diploids at elevated temperature and that triploids suffer similar blood disturbances after exercise as diploids. These findings have implications for the management of freshwater ecosystems and suggest that stocking triploid brown trout may offer an alternative to diploid brown trout.     

Flesh quality improvement in fish through breeding

In salmonids, which are fat fish, phenotypic and genetic parameters in flesh quality traits have been studied in several investigations while little has been done in other fish species. For traits like fat percentage, area of fat depot, and flesh colour in salmonids, relatively large genetic variation has been found. There is an unfavourable genetic correlation between body weight and the traits fat percentage and area of fat depot. The expected response to selection in quality traits, considering single trait selection, varies between 5 and 15% per generation. Quality traits can usually be recorded only on dead animals, and therefore family selection mush be practised in a breeding programme.     

The effect of dietary energy level on growth and nutrient utilization by juvenile diploid and triploid brook charr,Salvelinus fontinalis

Triploids are used in aquaculture because they are sterile and do not undergo preharvest loss in flesh quality. Despite this advantage, they do not always perform as well as diploids when fed commercial diets. This study investigated whether differences in dietary energy utilization might explain this reduced performance. Dietary lipid levels were adjusted to supply diets with 22.7, 23.6 or 24.4 MJ kg^?1 gross energy and fed to juvenile diploid and triploid brook charr. Fish were fed to satiation twice daily in a 70‐day growth trial, with samples collected at days 0 and 70 for proximate composition and plasma insulin‐like growth factor I (IGF‐I) analysis. This was followed by a digestibility trial using the same diets to determine apparent digestibility coefficients. Triploids had lower growth rates and condition factor than diploids on all three diets, but there was no effect of ploidy on feed conversion efficiency. Triploids also had lower whole‐body lipid content, but equal protein content, which resulted in lower energy content at both days 0 and 70. There was no effect of diet or ploidy on plasma IGF‐I concentrations. Triploidy did not affect diet digestibility, suggesting that the reduced performance of triploids is due to a difference in metabolism and energy utilization.     

Vaccination and triploidy increase relative heart weight in farmed Atlantic salmon,Salmo salar L.

Heart morphology is particularly plastic in teleosts and differs between farmed and wild Atlantic salmon. However, little is known about how different culture practices and sex affect heart morphology. This study investigated how vaccination, triploidy and sex affected heart size and heart morphology (ventricle shape, angle of the bulbus arteriosus) in farmed Atlantic salmon for 18 months following vaccination (from c. 50–3000 g body weight). In addition, hearts were examined histologically after 7 months in sea water. All fish sampled were sexually immature. Vaccinated fish had significantly heavier hearts relative to body weight and a more triangular ventricle than unvaccinated fish, suggesting a greater cardiac workload. Irrespective of time, triploids had significantly heavier hearts relative to body weight, a more acute angle of the bulbus arteriosus and less fat deposition in the epicardium than diploids. The ventricle was also more triangular in triploids than diploids at seawater transfer. Sex had transient effects on the angle of the bulbus arteriosus, but no effect on relative heart weight or ventricle shape. From a morphological perspective, the results indicate that vaccination and triploidy increase cardiac workload in farmed Atlantic salmon.     

Differences in metabolism of triploid and diploid Salmo trutta f. lacustris under acclimation conditions and after exposure to stress situations

Differences in metabolism (enzyme activities, metabolites) between diploid and triploid Salmo trutta f. lacustris were investigated under acclimation and stress conditions. Under acclimation conditions enzyme activities differed for 35% of the 27 investigated key regulatory enzymes and temperature optima for 23%. Muscle and liver metabolites related to energy metabolism and diagnostic indices of blood serum were similar, with exception of acetyl‐CoA being increased in triploids. Metabolic rate was lower and gill ventilation rate higher in triploids in comparison with diploids. During the tested stress situations (24 hr endurance swimming, 3 hr exposure to hypoxia in water with 32% oxygen saturation) muscle and liver glycogen decreased and serum and muscle lactate increased in both ploidy levels. Specifically, for triploids muscle adenylate energy charge and phosphocreatine levels decreased after endurance swimming and muscle and liver adenylate energy charge after exposure to hypoxia. Acetyl‐CoA increased in triploids during both stress situations. In summary, there existed differences in metabolism between the two ploidy levels and the energy metabolism of triploids was less balanced under stress.     

Comparative performance of growth,vertebral structure and muscle composition in diploid and triploid Paralichthys olivaceus

Growth, skeletal structure and muscle composition of cold‐shock‐induced triploid olive flounder Paralichthys olivaceus were investigated. The average values of total length and total weight of triploids were higher than those of diploids from 5 to 11 months posthatch (mph). The growth difference disappeared after 11 mph. The skeletal structure of flounder at 11 mph was observed by X‐ray imaging method. There are four kinds of vertebral deformity including vertebrae fusion, one‐sided compression, two‐sided compression and vertically shifted. The trunk region (V8–18) and tailing end of the vertebral column were the predominant locations of deformity. In general, the frequencies of vertebral deformities in triploids (60.0%) were higher than those in diploids (33.3%, p < 0.05). Both the number of fish with deformed vertebrae and the average frequencies of deformed vertebrae in triploids were significantly higher than those in diploids (p < 0.05). The muscle tissues of diploid and triploid flounder at 11 mph contain the same types of fatty acid and free amino acid profiles. The number of fatty acids with significant higher contents in diploids and triploids was one and ten, respectively (p < 0.05). The contents of free amino acids showed no difference between triploid and diploid fish.     

Total replacement of fish oil by soybean or linseed oil with a return to fish oil in Turbot (Psetta maxima): 2. Flesh quality properties

The aim of this study was to evaluate (1) the effects of replacement of fish oil by vegetable oils on flesh quality and (2) the effects of a washout with a return to fish oil on flesh quality of turbot. In a first period of 3 months, three isonitrogenous and isolipidic diets containing 9% of added marine fish oil (FO), soybean oil (SO) or linseed oil (LO) were fed to triplicate groups of 25 marketable size turbot (initial body weight: 579±1 g) grown in sea water at the temperature of 17 °C. At the end of the first period, all groups of turbot were fed with the diet containing fish oil (diet FO) for a further period of 2 months. The gutted and fillet yields were not affected by the incorporation of vegetable oils. However, soybean or linseed oils significantly affected the organoleptic quality of flesh particularly odour, colour and texture. A more pronounced potatoes odour and a lower fat texture were observed in dorsal fillet of turbot fed soybean oil diet. During the washout period, the differences observed between treatments in first period on sensory attributes disappeared. This study showed that the changes in organoleptic properties occurring due to the intake of vegetable oils can be reduced with a return to a fish-oil-based diet.     

Increased dietary phosphorous prevents vertebral deformities in triploid Atlantic salmon (Salmo salar L.)

Triplicate groups of triploid and diploid Atlantic salmon were fed diets with a low (LP, total P: 7.1 g kg^?1), medium (MP, total P: 9.4 g kg^?1) or high (HP, total P: 16.3 g kg^?1) phosphorous (P) level from first feeding (0.18 g) to transfer to sea water (~50 g, duration: 203 days) and subsequently fed a commercial diet in sea water for 426 days (~3 kg). This study examined the short‐ and long‐term effects of dietary P on freshwater performance (mortality, growth), vertebral deformities (radiology), bone cell activity (ALP and TRACP enzyme activity in vertebrae and scales, and fgf23, bgp and igf‐I relative gene expression in vertebrae), bone mineralization (ash content) and some parameters related to fish condition (heart and liver size). Irrespective of ploidy, at seawater transfer, fish fed the MP diet had significantly highest length and weight and those fed the LP diet significantly lowest length and weight, while those fed the HP diet had intermediate lengths and weights. Increased dietary phosphorus reduced deformities in both ploidies at seawater transfer; however, triploids fed the LP and MP diets had more deformities than diploids fed the respective diets, while there was no ploidy effect observed for fish fed the HP diet. The vertebral bone ash content at seawater transfer was significantly higher in diploids than in triploids when fed the MP diet only. Alkaline phosphatase (ALP) and tartrate‐resistant acid phosphatase (TRACP) enzyme activities and relative gene expression of bone hormones involved in metabolism of plasma phosphate (fgf23) and bone growth (bgp) were not affected by ploidy at seawater transfer, but by dietary P level; LP increased ALP activity and reduced TRACP activity and fgf23 and bgp expression levels in vertebral bone. In scales, LP increased both ALP and TRACP activity. At the termination of the seawater period, the group‐wise pattern in occurrence of vertebral deformities was the same as at seawater transfer. The present results on mortality, growth, bone mineralization and development of skeletal deformities all demonstrate that triploids have a higher P requirement than diploids in fresh water. This study shows that an optimalization of P nutrition for triploid Atlantic salmon can improve health and welfare and reduce down‐grading of triploid salmon.     

Quality characteristics in raw and smoked fillets of Atlantic salmon, Salmo salar, fed high-energy diets

Atlantic salmon, Salmo salar , were fed four levels of dietary fat (256, 308, 346 and 389 g kg⁻¹ of diet) for 138 days, with the purpose of studying quality characteristics in raw and smoked fish fillets. Dietary fat levels up to 346 g kg⁻¹ resulted in increased fat content of the raw fillets. The dietary fat levels had a less systematic effect on perceived fatness of the smoked fillets and caused a trend towards better odour and flavour. The fat content of raw fillets was significantly ( P ≤ 0.05) correlated to lower smoke odour, greater rancid flavour, fatness, and a yellower hue of the smoked fillets. Astaxanthin levels of the raw fillets varied between 6 and 11 mg kg⁻¹ of fillet and were significantly ( P ≤ 0.05) correlated with greater intensity of smoke odour, lower off-odour, and less whiteness, greater colour intensity and a redder hue of the smoked fish. It is proposed that salmon fillets can be graded according to weight, fat content and colour values prior to smoking to obtain more standardized quality characteristics of the final product after processing.     

Improvement of flesh quality in rainbow trout (Oncorhynchus mykiss) fed supranutritional dietary selenium yeast is associated with the inhibited muscle protein degradation

Supranutritional dietary selenium (Se) has been demonstrated beneficial for fish health, however, its effects on fish flesh quality remain unclear. This study investigated the effects of supranutritional dietary Se on the flesh quality of rainbow trout (Oncorhynchus mykiss) and their potential mechanism. Fish were fed a basal diet supplemented with or without graded Se yeast for 10 weeks. Results showed that Se supplementation significantly increased fillet crude protein and enhanced fillet water‐holding capacity as well as fillet firmness. Supplementing with both 2 and 4 mg/kg Se significantly downregulated the expressions of two autophagy–lysosome‐related genes (autophagy‐related 12‐like and gamma‐aminobutyric acid type A receptor‐associated protein‐like 1) in fish muscle, while supplementing with 4 mg/kg Se also significantly downregulated the expression of two ubiquitin–proteasome‐related genes (muscle RING finger 2 and F‐box protein 25). Correlation analysis indicated that the improved fillet quality parameters were closely correlated with the expressions of these differentially expressed genes. This study revealed that dietary Se was effective for the improvement of rainbow trout flesh quality, and the improved fish flesh quality was associated with the inhibited protein degradation in fish muscle.     

Seasonal changes in muscle structure and flesh quality of 0+ and 1+ Atlantic salmon (Salmo salar L.): impact of feeding regime and possible roles of ghrelin

Growth performance, muscle cellularity, flesh quality, and plasma ghrelin were investigated in 0+ and 1+ farmed Atlantic salmon (Salmo salar L.) from 40 g to 4.3 kg. Reduced meal frequency was introduced in both smolt groups from ~1.5 kg; one meal per second day (<5 °C) to one daily meal (>5 °C), while control groups were fed one to three daily meals. Results show that 0+ salmon had higher final fibre number and density, pigment content, red colour intensity, firmer flesh, and lower fillet fat content than 1+ salmon at 4.3 kg, affected by season and smolt type. Muscle fibre recruitment was an important determinant of fillet firmness and colour, possibly influenced by the prenatal temperature regime. Fish fed reduced meal frequency showed temporal reduced feeding ration, but growth performance was not compromised in any smolt groups at harvest. However, fillet fat, gaping, and colour decreased by less frequent feeding, with permanent effects in 1+ salmon for gaping and fat. Reduced meal frequency is therefore considered to be a promising tool for managing important flesh quality attributes in salmon without compromising growth performance. It is also suggested that ghrelin stimulates short‐term appetite, and perhaps also in the longer term.