Aquaculture Europe 2021

October 4 - 7, 2021

Funchal, Madeira

Add To Calendar 06/10/2021 11:50:0006/10/2021 12:10:00Europe/LisbonAquaculture Europe 2021IMPACT OF THERMAL SHOCKS DURING INCUBATION ON EGG DEVELOPMENT AND JUVENILE PERFORMANCE IN DIPLOID AND TRIPLOID ATLANTIC SALMON Salmo salar SIBLINGSCongress HallThe European Aquaculture Societywebmaster@aquaeas.orgfalseDD/MM/YYYYaaVZHLXMfzTRLzDrHmAi181982

IMPACT OF THERMAL SHOCKS DURING INCUBATION ON EGG DEVELOPMENT AND JUVENILE PERFORMANCE IN DIPLOID AND TRIPLOID ATLANTIC SALMON Salmo salar SIBLINGS

C. Howard*, J. Taylor, M. Bekaert, B. Craig, M. Mommens, M. Medina, H. Migaud

Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, Scotland, UK      

E-mail: callum.howard@stir.ac.uk

 



Introduction

Triploidy remains the only accepted method of producing sterile salmon for human consumption in Europe (Benfey, 2016). Triploids are historically believed to be inferior to diploids (Leclercq et al., 2011; Benfey, 2016), however new knowledge on triploid biology led to improved husbandry and nutrition and subsequently performance of triploid stocks (Fraser et al., 2013; Taylor et al., 2013). Triploids require lower egg incubation temperatures than diploids for optimal bone health (Fraser et al., 2015; Clarkson et al., 2020) and they are more sensitive to higher temperatures later in life (Atkins & Benfey, 2008; Hansen et al., 2015). This study aimed to study the impact of acute thermal shocks during egg incubation and explore how these impact the transcriptome, epigenome, and performance later in life. Such new fundamental knowledge will contribute to understanding how early life history may impact on long term phenotypes and support the development of ploidy specific husbandry in triploid salmon produced commercially. 

Material and Methods

A total of 7,200 Atlantic salmon eggs were stripped from a single female (Aquagen) and split into 2 batches. After fertilisation by a single male, 1 batch was triploidised using hydrostatic pressure (9500 psi for 6.25 min at 8°C, 37.5 min post-fertilisation) and the other was handled similarly but not triploidised. Both batches were incubated at 4 °C until eyeing (357 °/days) at which point they were transferred to the Institute of Aquaculture (IoA), University of Stirling, Scotland. Eggs were split into 24 tanks (300 eggs per tank) and after 24hr acclimation at 6 °C, three thermal shock treatments consisting in either 1 hr, 6 hr or 1 hr daily for 5 consecutive days at 10 °C were applied in triplicate with a control (egg handling but no thermal shock). During the thermal shock the eggs were subjected to an acute temperature shock from 6 to 10 °C and then back down to 6 °C. After the shocks, eggs were taken back to the tank, the temperature remained at 6 °C until just before first feeding at which point it was raised to 12 °C (1 °C/day). Fish were grown out for 7 more months. To test for the impact of the early temperature shock (thermal programming and memory), fish were challenged to an increase temperature of 16 °C (1°C/day increase) for three weeks. Feed intake was recorded daily in each tank throughout the experiment. Finally, to test for fish immune response, a PAMPS challenge (I.P. injection of 5 µg/g of Poly I:C, n=3, 6 fish per treatment with an additional 6 control fish injected with PBS) was performed.

Samples (eggs) were taken before and after shocks (7 days) for Reduced representation bisulfite sequencing (RRBS) and RNA-seq analysis to analyse the effects of the thermal treatments on both genome-wide methylation and transcriptomic profiles. Growth performances were analysed and X-rays were taken from 48 fish per tank for deformity analysis. Blood samples were taken before and after the thermal challenge for stress biomarker analysis. Liver samples were taken before and after thermal challenge for RNA-seq. Head kidney samples were taken before and after (24 hrs) Poly I:C injection for qPCR analysis of immune related genes.

Results

Diploids exposed to the repeated thermal shock treatment exhibited significantly more premature hatching (<430 °/days) than the control (P=<.001). Thermal treatment did not affect radiological vertebral deformities. In the triploid groups, total feed intake and final weight were higher in the 6 hr and 1 hr treated fish but not significantly so. Total specific growth rate was highest for the 6 hr treatments of both ploidies at both temperatures but not significantly.

Triploids suffered more pins and runts and weighed less at 1st feeding. Triploids also hatched earlier, with all tanks reaching 90% hatch 2 days earlier than any diploid tank.  At both 12 °C and 16 °C, triploids ate more than diploids overall, although this difference disappeared at 16 °C. At the end of the experiment triploids weighed significantly more than diploids. Radiological vertebral deformities were relatively low but were significantly higher in the triploid than the diploids. No cases of aplasia of the septum transversum were observed despite the thermal treatments.

qPCR (PAMPS challenge), RRBS (egg temperature treatments) and RNA-seq (high temperature challenge) analyses are underway and results will be presented at the conference. 

Discussion

The thermal shocks had a limited negative impact on the performance of both ploidies. With the exception of higher premature hatch in the repeatedly shocked diploids and higher egg drop out in triploids, no differences between treatments in terms of deformity or later mortalities were observed. Given the known sensitivity of triploids to higher incubation temperatures (Clarkson et al., 2020), this result is promising and suggests that triploids are reasonably tolerant to short term acute changes from optimal incubation temperatures after eyeing. Whilst there was a significantly higher level of radiological vertebral deformities in triploids, this number was considerably lower than seen in previous studies (Fraser et al., 2015), this is likely due to the fact that the eggs were incubated at 4 °C until eyeing. Whilst there was a higher level of pin fry in triploids, survival between ploidies was comparable. Some evidence of thermal programming was apparent with the triploid 6 hr group final weight being on average 6.5 % higher than the control. Ongoing qPCR, RNA-seq, and RRBS analyses will shed more light onto the epigenetic and transcriptomic impact of the thermal shocks.

Bibliography

Atkins, M. E., & Benfey, T. J. (2008). Effect of acclimation temperature on routine metabolic rate in triploid salmonids. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 149(2), 157-161.

Clarkson, M., Taylor, J. F., McStay, E., Palmer, M. J., Clokie, B. G. J., & Migaud, H. (2021). A temperature shift during embryogenesis impacts prevalence of deformity in diploid and triploid Atlantic salmon (Salmo salar L.). Aquaculture Research, 52(3), 906-923.Fraser, T. W., Hansen, T., Skjæraasen, J. E., Mayer, I., Sambraus, F., & Fjelldal, P. G. (2013). The effect of triploidy on the culture performance, deformity prevalence, and heart morphology in Atlantic salmon. Aquaculture, 416, 255-264.

Fraser, T. W. K., Hansen, T., Fleming, M. S., & Fjelldal, P. G. (2015). The prevalence of vertebral deformities is increased with higher egg incubation temperatures and triploidy in Atlantic salmon Salmo salar L. Journal of fish diseases, 38(1), 75-89.

Hansen, T. J., Olsen, R. E., Stien, L., Oppedal, F., Torgersen, T., Breck, O. & Fjelldal, P. G. (2015). Effect of water oxygen level on performance of diploid and triploid Atlantic salmon post-smolts reared at high temperature. Aquaculture, 435, 354-360.

Leclercq, E., Taylor, J. F., Fison, D., Fjelldal, P. G., Diez-Padrisa, M., Hansen, T., & Migaud, H. (2011). Comparative seawater performance and deformity prevalence in out-of-season diploid and triploid Atlantic salmon (Salmo salar) post-smolts. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 158(1), 116-125.

Taylor, J. F., Sambraus, F., Mota-Velasco, J., Guy, D. R., Hamilton, A., Hunter, D. & Migaud, H. (2013). Ploidy and family effects on Atlantic salmon (Salmo salar) growth, deformity and harvest quality during a full commercial production cycle. Aquaculture, 410, 41-50.