Smoltification (also known as Parr-Smolt transformation) is a complex series of physiological changes where juvenile salmonid fish adapt from living in fresh water to living in seawater. Fish transfer during the appropriate ‘smolt window’ provides the best opportunity for successful seawater adaptation.

Smoltification index

The most important physiological change during smoltification is the increase in hypo-osmoregulatory ability. It is due to anatomical changes in gills, kidney, and gut accompanied by physiological changes. These changes can be assessed using clinical chemistry.

Using algorithm-based AI modelling, WellFish Diagnostics is developing a new method to assess the optimum smolt transfer window based on the expression of a suite of clinical chemistry biomarkers related to a range of physiological changes that occur during smoltification.

Generally, blood samples are collected 6, 4, 2, weeks and on 7 and 2 days before the planned transfer date, but this can be tailored to meet your needs. Samples are analysed upon receipt at the lab and the data presented via our secure login customer portal within 24h, enabling rapid decision making. Results can also be submitted from saltwater tests to ensure optimal osmoregulatory function.

Atlantic Salmon Par Salmo Salar 800
Atlantic salmon

Chloride & osmolality Levels

The first week in saltwater is crucial for the survival of salmonids. This is when high mortality rates can occur, mainly due to osmoregulatory challenges. Saltwater causes increase in plasma ion level followed by tissue dehydration. Smoltification ensures physiological changes in osmoregulation mechanisms of anadromous fish to overcome this problem.

Electrolyte levels and in particular chloride and total osmolality in blood serum/plasma are used to indicate smoltification and readiness to transfer to seawater pens. In particular, results for chloride can indicate any osmoregulatory challenges. As well as our Smoltification Index, we present levels of individual electrolytes, graphed over time to help identify the optimal window for smolt transfer.



Health monitoring

Blood samples can be routinely submitted for health assessment of both parr and smolt from freshwater lochs, flow through and recirculation systems. This can be particularly useful for the early identification of furunculosis caused by the presence of the pathogenic bacterium Aeromonus salmonica.

More and more farms are relying on Recirculating Aquaculture Systems (RAS) for smolt production with a marked increase in the number of cases diagnosed with Nephrocalcinosis, traditionally diagnosed based on histological detection of calcium like deposits along with macroscopic detection during necropsy. Water quality and CO2 levels have been identified as risk factors. As part of the suit of biomarkers, levels of calcium and carbon dioxide (bicarbonate) in the blood can be used to detect the early onset of Nephrocalcinosis, monitor its progression and test the efficacy of remedial actions.


Data presentation

As with the clinical chemistry data generated by WellFish Diagnostics, the data generated the freshwater and smoltification phase is presented via our secure, customer specific, intuitive website portal. Results are graphed and presented for a single timepoint and over time to enable trends to be identified.

Fish health and smoltification information generated by our bespoke AI model are also presented graphically with all data available via a spreadsheet to facilitate integration into your fish health management system.

Contact WellFish Diagnostics for more information.