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20 Ton Tilapia Farm – Part 4 – Mortality

In our previous stage Production Staging, we worked through the biosecurity, growing stages, and growth of our fish in our farm design.  Now we go into detail mortality losses, intentional and unintentional, and how they impact our 20 ton Tilapia farm design.  This is where inexperienced designers make a fundamental mistake.  One I will help you avoid in your planning. In any farm we can expect that some fish are going to die.  As much as conscientious farmers do not like animals dying in their care, it is a fact of commercial fish farming.  One of my friends like to quote a very old fish farming statement “you are not a fish farmer until you have killed a million fish”.    I strongly disagree with him on this one, but the statement does have some truth to it. Losses on our farm are a big concern.  There are unintentional ones which are driven by species where carnivorous fish like to “protein share” or attempt to eat each other and they will have a higher mortality rate.  Young fish of all species suffer from higher losses, the smaller the larger the losses and most young ones are agressive toward available feed.  These tend to be out of our control and would be considered “natural”. The unintentional losses that are not natural are system and management related.  Generally the higher the skill the less losses but experience will not guarantee no losses but an experienced fish farmer will suffer less than those inexperienced.  Your experience may be something to consider when designing your farm and be realistic. Just because you grew a few fish in your backyard, does not make you an aquaculturist.  While it will give you a head start on those that have never grown fish, at a commercial level, especially at higher density, it counts for very little.  That may be a hard truth to swallow for some, but put that aside especially in your first year and expect to lose fish at a higher rate. The density at which you operate the farm will impact on your losses as well.  Not just the risk of disease but the general stress of the fish is much higher and your response time to critical issues is much shorter.  Take this into consideration when designing your farm.  You can certainly design it to operate at a higher density than you may be comfortable with and I recommend doing just that.  However in your first season you will want to run at a lower density to get your husbandry skills up, if they are lacking or consider hiring someone with the experience your farm needs.  Again I will remind you, it takes skill to grow fish commercially, please do not fool yourself, as I have seen some do, into thinking it is easy.  Any successful fish farmer will tell you differently. Experience Sidebar: One of our clients quite a few years ago, had never farmed fish (they are successful broad acre farmers), they gained 2 full weeks experience on a commercial farm before we built theirs.  We then extensively trained them on their own farm.  The farm was stocked with fish we had already partially grown at a reasonably safe density. I receive a call late at night from our client saying their fish are dying.  So I jump in my car and head out to the farm in the middle of the night (trust me you will have many sleepless nights in your first year).  We knocked out a tank of fish to take a closer look.  A large percentage of them had bite marks on their bum and were suffering from a bacterial infection which had spread into a fungus infection.  The fish were dropping like flies. We had to treat the 12,000 kg of fish immediately, in the middle of the night and I spent the remainder of the night in a swag in the fish shed.  The next day we had to determine what the cause of this was.  So I observed our new farmers in their daily routines… and one thing stood out like a Rhino in a playground. They were feeding a tank with 750 kg of fish (predators), one pellet at at time.  You can imagine what that looks like to the fish.  One pellet (large ones) hitting the surface of a tank full of ambush predators.  One fish gets the pellet then the others all start to attack each other.  To cut this story short, no matter the treatment they lost all of the fish and they are buried way up the back.  Then they had to start all over again, putting them 12 months behind.  They are still in operation today but a hard and expensive lesson learned. So the moral of this story is, even with intensive on farm training and some hand holding from experienced operators like us, it was not enough to avoid such a simple mistake.  Something to consider when you attend a 5 day “workshop” on aquaponics presented by people that have never grown anything commercially in their life…. Let’s get back to the mortality on our farm.  We know from the size of the fish, the weeks in production and our annual production we need 3846 fish at our final harvest.  When we work that backwards and apply our estimate losses (intentional and unintentional) in each stage we need to stock 5453 fish in each cohort.  Remember that we want to be sure we reach our yearly production goals and to stock with only  the fish required may see you with a short fall at the end of the year.  Your suppliers and your financial estimates will not be happy with that. However, again we are balancing between reality and our estimates.  The mortality estimates must be consider within reason but they should not overly impact your cost with a negative outcome.  For example, let’s assume we are paying $0.50 per fingerling.  If we have an overall loss of 29.46% (round it to 30%) our end cost for each kg produced will increase with it. In this example at $0.5 per fish our cost each cohort is $2,730 and we will have 10.4 of them in a year giving us a fingerling supply cost of $28,400 per year.  We are producing 20,000 kg per year and our cost center, which we will cover in detail later, is 1.42 per kg just for the fingerlings alone even though each fish only cost us $0.5 each.  If all the fish survived it would only cost us $1 per kg.  So you can see a 30% mortality will cost you an additional 42% for that supply line or an additional $8400 per year operational cost. The Common Errors This error is something I see a lot with budding designers.  They design their system, for example, to cope with the load of 10,000 fish at X grams weight.  They then assume they will lose a percentage of those fish, which may be expected, then add that percentage to the amount they put in the system.  Then discover, their mortality was much lower than predicted and their system design could not cope with the additional biomass. When the life support systems peaked, they had “mysterious deaths”.  You can see how this oversight can land you in a world of hurt. The other side to this error is design and stock the harvest numbers you need.  Nothing worse than designing a 20 ton per year farm, stock it with only the fish numbers you need, lose 30% of them and end up only producing 14 ton which is way short.  The impact to your bottom line can be difficult to recover from especially the larger the farm gets. The mortality estimates are only to be sure you reach your production goals and not fall short.  They are only used in the design for each stage if you plan to intentionally cull the balance of the fish mortality between stages.  Culling intentionally is common practice to “weed” out the runts in the stock that just wont grow well no matter the amount of feed you throw at them.  Most of the time this is done following grading out of quarantine or in the first stage after depending on the production staging on the farm. It is not uncommon to get poor genetic stock mixed in the batches.  In carnivorous fish, these are quickly “weeded out” by the faster growing fish through “protein sharing”.  This is why it is essential to track losses in all stages and tank and keep good record of these for culling calculations later. If you are not culling.  I know that sounds harsh, but to feed fish that will not grow and take up space and energy for the fish that will sometimes makes no fiscal sense.  However, culling may not be needed, although you will be culling around 10 per week to take measure and check the health of the rest of the stock, so definitely include this in your calculations.  In our scenario, that checking of stock will amount to 350 fish or around 5 to 6%.  If this is your farm and you plan not to cull be careful with your mortality estimates and design the farm to the maximum loading ignoring the losses in your design. When you have shared life support for each stage, like in our case, once the fish leave the quarantine, the number leaving their is the design number you will use regardless of any small losses through the grow out stages.  We will look into this a little closer when we cover the detailed feeding schedule before the biological design. Next we will look at the stocking calculations which will determine our tank sizes and later our life support systems….

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