Deriving value from otherwise sunk costs

As the old farming adage goes “Where there is livestock, there is deadstock.” 

Though we should always strive to optimize fish husbandry, establish and institute biosecurity protocols, and regularly monitor the health of our animals, some fish will not make it to market. These mortalities (commonly called “morts”) add to the cost of production. 

Depending on how many fish have died and how much has been invested in them, the cost of mortalities can be significant, and there can be severe impacts on an operation’s ability to achieve production goals and commitments to customers. In most cases, these costs cannot be recouped. However, by tracking and trending mortality numbers and classifying them based on their suspected cause of death, we can gain a better understanding of the health of our fish, prevent further loss, and derive some value from them. 

At the core of mortality management is regular (daily) monitoring of our livestock. Not only do we need to keep a close eye on the fish swimming in the water, we also need to observe and collect the morts; this is true for all stages of production, from early rearing troughs in a hatchery, to large tanks and cages. 

Mortality monitoring and collection has typically been a much greater challenge in cage-culture than in land-based facilities, where tanks are generally smaller and mortalities are more easily observed and collected. Traditionally, utilizing divers and “mort socks” or nets has been the way morts have been monitored and collected in cages, though it is impractical and too expensive to do this daily. 

These mort dives result in bringing up fish of varying states of decomposition through the water column and schools of swimming fish to the surface. Most of these morts are far too decomposed to examine and derive much meaningful information from. Although divers still play an important part in many cage operations, an increasing number of tools and technology are available to fish farmers to help better address these challenges with mortality management. 

Underwater cameras are an important tool for fish health monitoring, particularly in large tanks and cages. Many cameras can now be easily adjusted to different depths and angles, giving farmers a full view of their cages with the click of a button. Mortality retrieval systems have also enabled aquaculture operations to regularly collect their morts. There are also remote operated underwater vehicles (ROVs) available on the market to help monitor and collect mortalities. Although these technologies can be expensive and contribute to the cost of production, missing early cues to developing fish health problems can cost far more.

The importance of daily mortality collection cannot be overstated. Removing mortalities from your rearing system as soon as possible decreases their negative impacts on fish health, including the possible spread of pathogens and effects on water quality. The timely removal of morts also optimizes their physical condition, allowing for a more informative and valuable post-mortem examination. The daily collection of mortalities is essential for proper fish health management and biosecurity, and the ability to do so should be considered an absolute necessity by fish farmers. 

There will of course be situations out of a farmer’s control when mortality retrieval cannot occur, such as bad weather or machine/generator breakdowns; this is understandable but should be limited as much as possible. To put it bluntly, mortality collection should be considered as important as feeding your fish, and should not take a back seat. Furthermore, allowing your fish to decompose to the point that they float to the surface or rot through the cage should never be seen as a viable alternative to timely mort collection. 

In addition to collecting morts daily, it is critical to record the number of mortalities and to code or classify them based on a post-mortem examination. Even a basic post-mortem exam will give you some indication as to what that fish died (or did not die) from. This exam should include an external evaluation of the mort, including overall appearance, size, body condition, gill condition, skin and fin condition, etc. If the fish is large enough to do so (generally over 10-20 grams), cutting them open is recommended. This information can be tracked and trended, and can help inform management decisions and anticipate fish health issues based on previous mortality patterns. 

Some common classifications include “fresh” or “silver” for fresh morts with no obvious cause of death or signs of disease, various environmental causes (e.g. low oxygen, plankton, diatoms, pollen, etc.), specific predators (e.g. racoon, mink, heron, sea lion, etc.), “poor-performer” for fish that are smaller than the population, not growing or performing well, “fungus”, “mechanical” (for physical damage), any specific disease which has been previously diagnosed by a veterinarian (e.g. bacterial coldwater disease, Tenacibaculosis, bacterial kidney disease, etc.), and “non-codable” for any mortality too decomposed to assess. 

Most, if not all, aquaculture data management systems include a mortality coding option. Specific codes will vary depending on the system and can be adjusted and optimized by producers to best fit their operation. Although you want to have as extensive of a classification list as is practical, having too many classifications can make the process inefficient, confusing, and frustrating for farm staff. 

Your veterinarian would be happy to work with you to develop a practical and effective mortality classification system which is relevant to your operation. By performing post-mortem examinations, classifying morts and tracking this data, we can derive value from an otherwise sunk cost of production.  

Dr Mykolas Kamaitis is a private practice aquaculture veterinarian and owner of Belwood Lake Veterinary Services in Ontario, Canada. He previously worked in the salmon industry in British Columbia as a vet and Fish Health Manager with Mowi Canada West. During his time at Mowi, Mykolas developed a strong background in production medicine and continues to take a preventative and production-focused approach to fish health management. He was named president of the Association of Aquaculture Veterinarians of British Columbia (AAVBC) in 2018 and continues in the role to this day.