Optimal swimming speeds reflect preferred swimming speeds of brook charr (Salvelinus fontinalis Mitchill, 1874)

Several measures have been developed to quantify swimming performance to understand various aspects of ecology and behaviour, as well as to help design functional applications for fishways and aquaculture. One of those measures, the optimal swimming speed, is the speed at which the cost of transport (COT) is minimal, where COT is defined as the cost of moving unit mass over unit distance. The experimental protocol to determine the optimal swimming speed involves forced-swimming in a flume or respirometer. In this study, a 4.5–m-long tilted raceway with gradually increasing upstream water speed is used to determine a novel, behaviourally based swimming parameter: the preferred swimming speed. The optimal swimming speed and the preferred swimming speed of brook charr were determined and a comparison of the two reveals that the optimal swimming speed (25.9 ± 4.5 cm s−1 or 1.02 ± 0.47 bl s−1) reflected the preferred swimming speed (between 20 cm s−1 or 0.78 ± 0.02 bl s−1 and 25 cm s−1 or 0.95 ± 0.03 bl s−1). The preferred swimming speed can be advantageous for the determination of swimming speeds for the use in aquaculture studies

The production of triploid landlocked Atlantic salmon (Salmo salar L.) and their potential for aquaculture

Heat shocks of 5 minutes at 32°C or hydrostatic pressure shocks of 3 or 6 minutes at 7.0 x 10⁴ kPa (10,150 p.s.i.), when completed within 20 minutes of fertilization at 10°C, were found to induce 100% triploidy with 70-90% survival (relative to controls) in eggs of landlocked salmon (Salmo salar L.). The identical heat shock yielded substantially lower numbers of triploids when applied 25 to 45 minutes after fertilization. Pressure shocks of longer duration (9 to 15 minutes at 7.0 X 10⁴ kPa) or higher magnitude (6 minutes at 7.9 X 10⁴ to 10.5 X 10 4 kPa) resulted in 100% mortality prior to hatching. The duration of the effective period within which heat shocks could be used to induce triploidy was found to be temperature dependent, being longer at 6.5°C than at 10°C. Attempts to induce polyploidy with cytochalasin B were unsuccessful. -- Karyotyping was not a useful method for the routine identification of triploids because it was time-consuming and inconsistent. The use of a microspectrophotometer to measure the DNA content of Feulgen-stained erythrocytes, although time-consuming, clearly distinguished triploid from diploid fish. Blood cell sizing by means of a Coulter Counter Channelyzer was a highly effective alternative to screen for triploids, being both fast and accurate. This technique was routinely used to identify triploid individuals. The use of various erythrocyte dimensions measured from blood smears was a valid method for indentifying triploids, but was also time-consuming. No mosaic polyploids were found, and the existence of such fish is questioned. -- Triploid fish had a greater mean erythrocyte volume (MCV) but lower erythrocyte count than diploids; the haematocrit was thus the same in diploids and triploids. Although the total blood haemoglobin content and the mean corpuscular haemoglobin concentration (MCHC) were lower in triploids than in diploids, the mean corpuscular haemoglobin content (MCH) was higher than that of diploids. The increase in triploid MCV was mainly due to an increase in cell length; there was only a minor increase in cell width and no increase in cell height. The nucleus of triploid erythrocytes occupied a greater percentage of the corpuscular volume than did the diploid nucleus. Mean cytoplasmic haemoglobin concentration was found to be the same for diploids and triploids when this was taken into account. -- The rates of oxygen consumption by diploid and triploid fish were the same, as was the oxygen tension at asphyxiation. Growth rates (measured as change in weight with time) prior to spawning were the same for diploids and triploids, but diploids were consistently shorter in fork length, thus having a higher condition factor. The gonadosomatic index (GSI) of diploid females was 13 times greater than that of triploid females, but the GSI of diploid males was only 1.9 times greater than that of triploid males. Triploid ovaries had the appearance of gonads, but triploid testes were well-developed. Gonad histology revealed that diploid ovaries were packed with hundreds of previtellogenic oocytes (stages 1-4), whereas triploid ovaries contained mostly undifferentiated oogonia. Every triploid ovary examined, however, contained at least one oocyte having the typical diploid appearance, indicating that triploid females were not sterile. Triploid testes contained all the elements present in the diploid testes, but development appeared to be delayed in comparison to that of the diploids. -- It is concluded that triploid females may be of benefit to salmonid aquaculture, but that further studies of growth and maturation are required

The reproductive physiology of triploid Pacific salmonids

Triploidy was induced in rainbow trout, Salmo gairdneri Richardson, by heat shock (10 min at 26, 28 or 30°C, applied 1 min after fertilization at 10°C) and in pink salmon, Oncorhynchus gorbuscha Walbaum, and coho salmon, 0. kisutch Walb., by hydrostatic pressure shock (1, 2, 3 or 4 min at 69,000 kPa, applied 15 min after fertilization at 10.5°C). Triploid individuals were identified by the flow cytometric measurement of DNA content of erythrocytes stained with propidium iodide. Gonadosomatic index was reduced to a much greater extent in triploid females than males. Triploid ovaries remained very small, and contained virtually no oocytes. Triploid testes became quite large, but few cells developed beyond the spermatocyte stage. Triploid male rainbow trout had significantly lower spermatocrits than diploids, and their spermatozoa were aneuploid. Growth rates were the same for diploid and triploid rainbow trout, but triploid female pink salmon were smaller than maturing diploid females and diploid and triploid males of the same age. Triploid males of both species developed typical secondary sexual characteristics and had normal endocrine profiles for plasma sex steroids and plasma and pituitary gonadotropin, but their cycle was delayed by about one month. Triploid females developed no secondary sexual characteristics and showed no endocrine signs of maturation, even at the level of the pituitary. Vitellogenin synthesis was induced in immature diploid and triploid coho salmon by the weekly injection of 17β-estradiol. Plasma vitellogenin and pituitary gonadotropin levels were significantly elevated over levels of sham-injected fish, whereas plasma gonadotropin levels were slightly depressed. There was no significant difference between diploids and triploids for any of these results, indicating that normal vitellogenesis is not impaired by triploidy per se. It is concluded that triploids of both sexes are genetically sterile, but that only triploid females do not undergo physiological maturation. Triploid testes develop sufficiently for their steroidogenic cells to become active, which is not the case for triploid ovaries. The occasional cells that pass through the normal meiotic block develop to full maturity in triploid males but not in triploid females, probably due to the absence of the appropriate stimulus to initiate and maintain vitellogenesis. Although triploids of both sexes should make valuable tools for basic research on reproductive physiology, only the females will be useful for practical fish culture to avoid the economically detrimental effects of maturation in fish destined for human consumption.Science, Faculty ofZoology, Department ofGraduat

Growth and Gonadal Development in Triploid Landlocked Atlantic Salmon (Salmo salar)

There was no difference in weight between diploid and triploid landlocked Atlantic salmon (Salmo saiar) measured over a 9-mo period, but triploids were consistently longer (FL) and thus had a lower condition factor than diploids. The gonadosomatic index (GSI) of triploid females was only 7.7% that of diploid females, while the GSI of triploid males was 52% that of diploid males. Triploid ovaries had the external appearance of undeveloped gonads, but every triploid female did in fact produce a small number of oocytes (from 1 to 12, versus several hundred oocytes in each diploid female). Triploid testes were well developed but contained few spermatids and no spermatozoa. Diploid testes, on the other hand, were in advanced stages of spermiogenesis. None of the triploid males reached spermiation

Production of female triploid coho salmon

The aquaculture production of all-female triploid (sterile) populations is recognized as being of potential advantage for many species of fish where sexual maturation is not desired. All-female triploids have been produced by inducing triploidy in eggs that had been fertilized with monosex female sperm. However, monosex stocks to produce this type of sperm are currently available only for a limited number of economically important species. To circumvent this problem, an alternative method would be the direct fertilization of tripoid embryos. In Pacific salmon, pressure shocks applied shortly after fertilization have consistently resulted in high yields of tripoids, and feminization by direct estrogen treatment has also been shown to be highly effective if applied shortly after hatching. In this study, coho salmon eggs were made triploid by a pressure shock of 633 kg/cm2 for 4 min, applied 20 min after fertilization and incubation at 10 °C. Some of the resulting embryos were then feminized with estradiol-17β in single 2-hour immersion treatments at 400 μg/liter, administered 1 and 8 days after hatching. Six months later, when the fish were juveniles, analysis of the DNA content of erythrocytes by flow cytometry revealed a 100% induction of triploidy, while histological examination of the gonads showed 82% females, which were completely devoid of oocyte development and thus genetically sterile. These manipulations reduced survival during early stages of development but survival became stable later. Together, these results suggest that the production of sterile fish by direct feminization of induced triploids could be of particular advantage for those species in which all-female stocks are yet not available or difficult to obtain

The effect of triploidy on juvenile Atlantic salmon (Salmo salar) response to varying levels of dietary phosphorus

Although triploidy induction is a reliable method for producing sterile fish for aquaculture and fisheries management, little is known about how triploidy influences nutrition and bioenergetics of fish. The aim of this study was to determine whether triploidy affects nutrient uptake and body composition in fish, using juvenile Atlantic salmon (Salmo salar) as the test species and varying the levels of dietary phosphorus. Triplicate groups of sibling triploids and diploids (45. g initial weight) were fed isocaloric diets with 0.76, 0.99 and 1.39% total phosphorus in a 12-week growth trial, followed by a feed digestibility trial with diets having 0.67, 0.93 and 1.15% total phosphorus. Triploids had a higher growth rate and lower condition factor than diploids during the growth trial, with no difference in feed conversion ratio. Whole-body lipid and energy levels, as well as nitrogen and energy efficiency ratios, were higher in the triploids, but ash and moisture levels were lower. Triploids initially had lower plasma phosphorus levels than diploids, but on the final sampling day there was no difference between ploidies in levels of plasma phosphorus, bone ash and phosphorus within the bone ash. Apparent digestibility coefficients for phosphorus, ash and dry matter were not significantly different between triploids and diploids. The observed effects of triploidy on growth and body composition therefore cannot be attributed to phosphorus utilization and metabolism.Peer reviewed: YesNRC publication: Ye

Gynogenesis and sex determination in Atlantic halibut (Hippoglossus hippoglossus)

Gynogenesis refers to a process of uniparental inheritance whereby the resulting offspring retain only maternal DNA. It has been used to identify sex-determining mechanisms in fish and to produce all-female populations for aquaculture. The objective of this study was to develop a protocol for the production of gynogenetic Atlantic halibut for both these purposes. Various milt concentrations (1:20, 1:40 and 1:80 dilutions in seminal plasma) and UV doses (0\u20131382 mJ/cm2) were tested for providing genetically inactivated, yet motile, spermatozoa for the production of gynogenetic haploids. Spermatozoon motility, assessed both as duration of swimming and percentage of motile spermatozoa, declined with increasing UV dose. Haploidy in developing embryos was determined either visually (\u2018haploid syndrome\u2019) or by genetic analysis using microsatellite DNA. The optimum milt treatment for the production of haploids was 1:80 dilution followed by a UV exposure of 65 mJ/cm2. Retention of the second polar body for the production of gynogenetic diploids was achieved by exposing newly activated eggs (15 min post-activation at 5\u20136 \uc2\ub0C) to hydrostatic pressure of 8500 psi for 5 min. These treatments were combined to produce a population of gynogenetic diploids that was subsequently demonstrated to be comprised solely of females, thereby demonstrating that female is the homogametic sex in this species. It should therefore be possible to produce all-female populations of Atlantic halibut for commercial culture through gynogenesis or by crossing hormonally masculinized genotypic females to normal females.Peer reviewed: YesNRC publication: Ye

Real-time PCR analysis of ovary- and brain-type aromatase gene expression during Atlantic halibut (Hippoglossus hippoglossus) development

Two forms of cytochrome P450 aromatase, acting in both the brain and the ovary, have been implicated in controlling ovarian development in fish. To better understand the expression of these two enzymes during sexual differentiation in Atlantic halibut (Hippoglossus hippoglossus), real-time PCR was used to quantify the mRNA levels of ovary- (cyp19a) and brain-type cytochrome P450 aromatase (cyp19b) genes in the gonad and brain during gonadal development. Both enzymes showed high levels of expression in both tissues in developmental stages prior to histologically detectable ovarian differentiation (38 mm fork length), with increased expression occurring slightly earlier in the brain than the gonad. Cyp19a showed a second peak of expression in later stages (> 48 mm) in the gonad, but not the brain. Cyp19b expression was generally higher in the brain than the gonad. These results suggest that sexual differentiation may begin in the brain prior to gonadal differentiation, supporting the idea that steroid hormone expression in the brain is a key determinant of phenotypic sex in fish. In an examination of sexually immature adults, cyp19a was highly expressed in female gonad while cyp19b was very highly expressed in the pituitary of both sexes. The ratio of cyp19a to cyp19b expression was much higher in ovaries than in testes in the adult fish, so this ratio was analyzed in the developing gonads of juvenile halibut in an attempt to infer their sex. This was only partially successful, with about half the fish in later developmental stages showing apparently sex-specific differences in aromatase expression.Peer reviewed: YesNRC publication: Ye

RNA-Seq Analysis of the Growth Hormone Transgenic Female Triploid Atlantic Salmon (Salmo salar) Hepatic Transcriptome Reveals Broad Temperature-Mediated Effects on Metabolism and Other Biological Processes

This study examined the impact of rearing temperature (10.5, 13.5 or 16.5°C) on the hepatic transcriptome of AquAdvantage Salmon (growth hormone transgenic female triploid Atlantic salmon) at an average weight of 800 g. Six stranded PE libraries were Illumina-sequenced from each temperature group, resulting in an average of over 100 M raw reads per individual fish. RNA-sequencing (RNA-seq) results showed the greatest difference in the number of differentially expressed transcripts (1750 DETs), as revealed by both DESeq2 and edgeR (q |1.5|), was between the 10.5 and 16.5°C temperature groups. In contrast, 172 and 52 DETs were found in the 10.5 vs. 13.5°C and the 13.5 vs. 16.5°C comparisons, respectively. Considering the DETs between the 10.5 and 16.5°C groups, 282 enriched gene ontology (GO) terms were identified (q < 0.05), including “response to stress”, “immune system process”, “lipid metabolic process”, “oxidation-reduction process”, and “cholesterol metabolic process”, suggesting elevated temperature elicited broad effects on multiple biological systems. Pathway analysis using ClueGO showed additional impacts on amino acid and lipid metabolism. There was a significant positive correlation between RNA-seq and real-time quantitative polymerase chain reaction (RT-qPCR) results for 8 of 9 metabolic-related transcripts tested. RT-qPCR results also correlated to changes in fillet tissue composition previously reported in these salmon (e.g., methionine and lysine concentrations positively correlated with hsp90ab1 transcript expression), suggesting that rearing temperature played a significant role in mediating metabolic/biosynthetic pathways of AquAdvantage Salmon. Many transcripts related to lipid/fatty acid metabolism (e.g., elovl2, fabpi, hacd2, mgll, s27a2, thrsp) were downregulated at 16.5°C compared to both other temperature groups. Additionally, enrichment of stress-, apoptosis- and catabolism-relevant GO terms at 16.5°C suggests that this temperature may not be ideal for commercial production when using freshwater recirculating aquaculture systems (RAS). This study relates phenotypic responses to transcript-specific findings and therefore aids in the determination of an optimal rearing temperature for AquAdvantage Salmon. With approval to grow and sell AquAdvantage Salmon in the United States and Canada, the novel insights provided by this research can help industry expansion by promoting optimal physiological performance and health