Testing of NKA expression by mobile real time PCR is an efficient indicator of smoltification status of farmed Atlantic salmon

Abstract

Assessment of seawater readiness of freshwater salmon smolts is a crucial husbandry step with economic implications in salmon aquaculture but current methods rely on delayed centralised enzymic activity measurement. The efficiency of a qRT-PCR assay for sodium potassium ATPase (NKA) α1a mRNA was tested in a 3-year study on 19 hatcheries across Scotland incorporating environmental factors such as temperature and metal contamination. The NKA qRT-PCR assay was transferred to a mobile laboratory and on-site testing was carried out at 3 hatchery sites. For the first two years standard enzymatic and gene expression assays had similar success rates in detecting smoltification (NKA activity 60%, qRT-PCR 57%). In the third year, all but one site were determined as sea water ready by qRT-PCR but only at 4 by enzymatic testing. On site testing with mobile qRT-PCR was successfully performed on four farm sites. Altogether, high sensitivity was shown for the in lab (98.9%, SE 0.24) and mobile (93.43%, SE 0.119) assays when tested using a quantitative RNA standard. Some indication for obscured smoltification assay results due to environmental increased heavy metal contamination was observed. Our results prove it is possible to test a smoltification marker on site and provide results on the day of testing during the smolt period allowing for informed decisions on seawater transfer.

New wine in old bottles: Modification of the Na+/K+‐ATPase enzyme activity assay and its application in salmonid aquaculture

“…Nevertheless, differential expression of NKAα-subunits or other ion transporters in all three osmoregulatory organs may provide useful biomarkers at the gene or protein level, particularly since the technology has become automated and more cost effective in recent years. However, the caveat with measuring mRNA abundance is that transcripts are often very sensitive and small changes in the environment, particularly ion composition, salinity and other water quality parameters [46][47][48] may result in changes in NKA-α1b/α1a ratios that not necessarily reflect a true smolt development. Furthermore, differential NKA isoform transcript expression may not reflect translation into protein and the activity of the mature enzyme, which limits the predictive power of mRNA expression as molecular markers.…”

Insight into real-world complexities is required to enable effective response from the aquaculture sector to climate change

“…Temperature and oxygen are important parameters for hatcheries and early stages [70][71][72][73], and it is important that conditions are kept within optimal ranges, and gradual temperature increases as well as heatwaves could affect inlet water quality. Changes in rainfall may also affect inlet water quality, for example runoff could lead to increased suspended solids [70], or metal contamination [74].…”

“…Increased temperatures and poor water quality may stress fish, impair development, and result in deformities [93][94][95][96][97]. Metal contamination in inlet water from precipitation/runoff affects the development of smolts and causes issues for seawater transfer [74,98,99].…”