Grouper Culture Using RAS - Calculations 2

In my last posting, we finally able to calculate the maximum standing stock (MSS) of our RAS for production of 12mt/year of grouper fishes. We should also be able to calculate the average standing stock (AvStS) of our system by doing the averaging calculation from month 1 of full batches production (i.e month 12 from the beginning of the farmig) to certain period of farming, which is based on my last calculation, I used to up to 16th farming month of full circle production, i.e month 26th. Let we see the table below:

Standing Stock

So, the AvStS will be 6149 kg through out 16 farming months and represent about 51% from targeted production. In my last post we calculated the MSS was at 7264kg or 61% from our targeted production. Bear in mind of these figures, which we will use to find the design peak load (DPL) of our system for most variables in our system i.e. oxygen supply requirement, carbon dioxide production, ammonia-N production, bio-oxygen demand (BOD) and suspended solids production. 

The maximum food given in MSS situation will be 94.43 kg/day while the average maximum food given in average standing stock (AvStS) will be 79.94 kg/day. The oxygen requirement for each kg of food given will be 350g while carbon dioxide produced per kg of food will be 1.2 times higher than the amount of oxygen consumed which is equal to 420g per kg of food given (350g x 1.2 times). Based on these facts, during MSS, the maximum oxygen consumption will be 33.05 kg/day while in average standing stock situation the oxygen consumption will be  27.98 kg/day. We also able to know now that carbon dioxide production in MSS situation will be 39.66 kg/day (350g/kg of feed x 94.43 kg of feed) while in average standing stock situation (AvStS) it will produce 33.57 kg of CO2/day (420g of CO2/kg of feed x 79.94 kg of feed). So, up to now, we already able to calculate our maximum standing stock, average standing stock, feed requirements during MSS and AvStS, the oxygen requirement during MSS and AvStS and lastly we able to calculate the carbon dioxide production in both situations of MSS and AvStS.

In next posting, I wish to share how to calculate the ammonia-N production, BOD and suspended solid going to be produced in our system.

Grouper Culture Using RAS - The Basic Calculations

Last week I visited 2 fish farms that using  recirculating aquaculture system (RAS). Interestingly, both have changed their species to another newly introduced species that having higher price and in demand in the local market. I like their idea of changing the species when the need arise. Having a better priced species is the rule of thumb no 1 in our RAS considerations, but surely is not the only factor that we must consider. More interestingly, they were changing from marine water species to fresh water species. That is the extra benefit of RAS. We may change the “climatic” conditions of our farming system without need to change the location or even the equipments.

What shall we know about RAS before we design it? First, off course the species that we intent to culture, their requirement or acceptable water quality. Please get the information on the acceptable levels of dissolve oxygen (DO), carbon dioxide (CO2), ammonia (NH4⁺ /NH3), nitrite ( NO2 -), nitrate (NO3-), suspended solids (SS) and salinity of our chosen species. Some grouper species have different tolerant towards fluctuation of the quality of some parameters. 

Second, we must quantify the target production over certain farming period (e.g: kg/month, mt/year). By knowing our targeted production, we may calculate the maximum standing stock (MSS), expected oxygen consumption and waste production from our system. We also will be able to calculate the water flow rate, solid and biological  filtrations systems. So, give our system a targeted production, say 12 mt/year.


Third, make a simulation standing stock for our 12 mt/year farm. Are we going to stock our juvenile in batches or all at one go? Say we are going to produce in 12 batches (1 batch/month) at 0.8kg/fish at 90% average survival rate. The survival rates for each month will be different. Normally, the fish survival will be higher when the reach bigger size. The farming period will be 8 month per batch. Therefor, we are going to stock  1280 fish juvenile/batch for each month.   If we are going to use fry of 50g each, in the first month we will have 51 kg of biomass in our system. Next month, with 83% of survival rate and average weight of 70, the same stock will grow becoming 158g each and the total biomass will become 168 kg. At the same time, the 2nd batch will weight 51 kg in biomass making total biomass in the 2nd month will be 219kg. The calculation goes on and on until we reach full 12 batches in the twelve month with biomass of 5034kg. Remember, we are going to sell our yield at the end of 8th month of each batches and restocking new fry in the next month. So, our calculation will results like this:

Standing Stock for 12 mt grouper farm with the Maximum Standing Stock (MSS). Table: Mahmud Ismail.

In order to know the highest standing stock of our system, we simulate the calculation until all batches in full operation. The highest standing stock for our system is 7264 kg which going to take place in the 16th month of operation. This value is called as Maximum Standing Stock (MSS) which indicates the highest load in our production in term of biomass of the fishes, maximum intake of feed and consequently the maximum waste formation. As can be seen, our MSS value is  around 61% of the targeted annual production.


Normally, we feed our grouper fishes around 1.2% to 1.5% of thier body weight per day (for calculation purpose, we use 1.3%). So, during the month 16, our Maximum Feed Consumption (MFC) will be: 7264 x 1.3% = 94.4 kg/day. However, in actual situation, the feeding rates varies according to the size of the fishes, at early stage (smaller size) the feeding rate normally higher then the feeding rate when the fishes are bigger in sizes.  


We shall continue later with calculation for oxygen consumption, carbon dioxide, biological oxygen demand (BOD), suspended solid and ammonia productions from this basic knowledge of MSS and MFC. Later, we shall also calculate the water flow requirement as well as the solid filtration system and the biological filter of our farm.  

Grouper Culture Using RAS - The Basic Processes

Without realising it, maybe most of us have been using recirculating aquaculture system (RAS) in our home aquariums for keeping our lovely ornamental fishes. So far, I rarely saw somebody using flow through system for their home aquarium. Did we study our aquarium system and how does it functioned to support the life of our aquarium fishes? If we did, perhaps it will be very easy for us to understand the RAS.

I believe everyone of us have some ideas about RAS, so I want to make the simplest explanation about RAS. The system work in a way where used water being moved into another cleaning system for cleansing purposes before being re-use back in the farming places. However, I used to see some system that do the cleaning process in situ, i.e. inside the farming tank itself. They move the water to some area of the farming tank and do the cleaning process before the water mixed back with the rest of farming water.

Why Go For RAS?
At least there are 5 reasons said in most of RAS textbooks on why people choose RAS for their fish (and aquatic organisms) farming system. Among the reasons is RAS can be operated in the unsuitable site for other type of farming. Since RAS normally a closed system, it will not depending so much on external factors. The internal environment perhaps can be "created" according to our species requirement. Second, it can be use in the area where water resources are poor, either in quantity or quality, either permanent or temporarily. RAS will not depending on external water resources to some extent. Third, it can be operated in the unsuitable climate for certain species. We can create our conducive internal climate in our RAS farm.  Fourth, we can control or have more control over our production.  Fifth, RAS can accommodate to environmental rules and regulations. However, for me, any other reasons such as logistic and market potential could also another reason why RAS was chosen. Personally, I choose the RAS because of the fourth factor, yes, I want to be in full control of my farm which I consider the most important aspect the fish farming management activities. I used to observe some other fish farming systems such as open water (sea, lake, lagoon and river) cages and ponds for groupers, seabass, threadfin, snappers, cobia and pompanos as well with molluscs and crustaceans. To my opinion, the open systems really can makes the management at the mercy of nature.

There will be few processes involved, mainly physical process in moving the used water into the cleaning place and physical, biological and chemical processes in the cleaning parts. We will see what are the processes involved in an recirculating aquaculture system (RAS) later (not including the biochemical processes that going to take place inside the body of our cultured organisms).

Function Of Water In RAS
As in the name of the system, it will recirculate  at least the water in the system (depending on how good the cleaning process of the system take place, otherwise, it will also recirculate some unnecessary element). Since we are keeping our groupers in the enclosed tanks, we must not only look at the water recirculating process   similar to air conditioning process in the a crowded places, but it work almost like the oxygen supply in the hospital intensive care unit. Our fishes will need the water as their living media and as their life support system. The recirculated water should bring along both basic functions, conditioning and life supporting. However, that 's not all the functions of the water in RAS. It will functioned as cleaning media for the system just equally to the same function of the blood in our body.  So, the recirculating of water will cover at least few processes: refreshing of living media, bringing in oxygen and cleaning the system.

The recirculating process in RAS normally done with the use of pumping system. We should discuss about the pumping system in RAS sometime later.

The Removing Of Unwanted Materials

When keeping our groupers in the tanks, they depends solely on the feeds given to them for their growth. We could be fully aware that every time we feed the fishes, there are some amount of the feeds were not eaten by the fishes. It will drop to the bottom of the tank, broken into pieces or swelled due to water absorption and some becoming the suspended solids in the water. At the same time, the fishes will excrete their metabolites through their feces. These will become our first problems, removing solid waste and suspended solid waste .After sometimes, the excess feed and faeces will disintegrated becoming smaller particles and require to be removed with other dissolved organic materials.

The breaking up of the uneaten feed will involve few physical and biochemical reactions or processes.The process of breaking up of feed and feces will require oxygen and this will creating demand for oxygen inside our system. Remember, our grouper fishes also require oxygen for their life and they also excrete carbon dioxide from their respiration process. 

The impact of the fishes on the farming water. Photo: Mahmud Ismail.

The eaten feed will be used by our fishes for growth and getting energy. In order to gain the energy, the feed components will be oxidized which will require oxygen and excrete carbon dioxide. Ammonia is another waste product of the breakdown of the protein in the feed. So, our fishes will consume foods and use oxygen for breathing and oxidation of the feed. The farming water will be the polluted with the uneaten feed, faeces, excretion of carbon dioxide and ammonia.

In the next posting, I will try to elaborate how cleaning processes being done in RASRAS or order from our supplier. Do not build or buy without knowing our real requirement of every components in RAS. We may end up building excessive or undersized components of our RAS. Since RAS is a life support system and life keeping system, anything below standard requirement will be hazardous to our grouper fishes while excessive mean more money needed for our initial investment, something that any investor will try to avoid.