Factors contributing to low embryo survival in Atlantic salmon (Salmo salar)

Factors contributing to low embryo survival in Atlantic salmon (Salmo salar)

Summary

Over the past decade there has been a decline in embryo survival in Maine’s hatchery reared Atlantic salmon, Salmo salar, for which causes are unknown. Due to the decline in embryo survival, hatcheries are no longer able to predict their yearly output preventing the sale of surplus eggs as an additional source of revenue. Causative factors for reduced embryo survival will be investigated in this project by measuring egg and maternal plasma hormone concentrations of estradiol (E2), 11-ketotestosterone (11-KT) and testosterone (T) and correlating these hormone concentrations with embryo survival. Hepatic and ovarian genes involved in toxin regulation and steroidogenesis will be measured as well as Ethoxyresorufin-O-deethylase (EROD) activity which provides an indication of contaminant exposure from xenobiotics.

Blood, liver, ovary and egg samples have been collected from 350 female broodstock Atlantic salmon during two spawning seasons from three Maine hatcheries. E2, 11-KT and T have been quantified in the plasma and eggs of each sampled female using radioimmunoassays or enzyme immunoassays. Positive correlations were found between the plasma hormones E2 and 11-KT with embryo survival whereas plasma testosterone, as well as E2, 11-KT and T measured in the egg, do not show any correlation with embryo survival.Anecdotal evidence at State hatcheries has suggested that adding calcium to the diet improves embryo survival in trout, therefore plasma and egg calcium concentrations were measured for each female; results show no correlation with embryo survival and calcium concentrations in the plasma or egg.Hepatic and ovarian gene expression for each female is currently being analyzed.

Objectives/Performance Targets

• Determine if maternal hormone concentrations correlate with embryo survival in cultured Atlantic salmon.
• Determine if maternal deposition of hormones into the egg correlates with embryo survival.
• Determine if egg calcium concentrations correlate with embryo survival.
• Determine if maternal deposition of calcium into the egg correlates with embryo survival.
• Determine if the expression of key genes involved in the production of steroid hormones correlates with embryo survival
• Analyze two biomarkers of contaminant exposure and determine if they correlate with embryo survival.
• Convey our findings to salmon hatcheries throughout the Northeast

Statistical analyses are currently being performed on the first four objectives listed above using the JMP software package. EROD activity has been measured as a biomarker of contaminant exposure showing no significant correlation with embryo survival. RNA is currently being extracted in tissues in order to look at gene expression.

Accomplishments/Milestones

September & October: Measured EROD activity in maternal livers

November & December: Learned how to extract RNA; extracted RNA from maternal livers and ovaries

 My project has progressed as expected in regards to the lab work and statistical analysis, however, I had expected to have already sampled more salmon females from this year’s spawning season, as described in the project’s original timeline. The hatchery should be ready in January for sampling. The accomplished lab work includes measuring EROD activity in the maternal livers as well as preparing liver, ovary and egg samples for gene expression by extracting RNA.

Another unexpected change to the project is if I will be able to measure FSH and LH levels in the maternal plasma. I expected to be able to collaborate with an expert at measuring FSH/LH in salmonids, however, the collaborator’s supplies were exhausted for analyzing my samples and therefore both assays could not be performed. This summer the collaborator will look into making more supplies in order for my samples to be analyzed. My advisor has suggested that I look into the methods for measuring FSH/LH in hopes of successfully performing the assays in our own lab just in case plans fall through with our collaborator.

Impacts and Contributions/Outcomes

The proposed objectives in this project have the ability to affect Atlantic salmon farming practices by saving time and money through creating more efficient spawning protocols as well as provide extra revenue through the sale of surplus eggs and fry.

 I have accepted an offer to present my project at the Bi-annual Salmonid Hatchery Roundtable in Belfast, Maine. I have also submitted the project’s abstract to the World Aquaculture Society (WAS) in hopes of presenting at their 2014 conference in Seattle, Washington. I received an email in December from WAS informing me of my abstract’s acceptance to the conference.

Collaborators: