There are certain errors that are commonly made by new entrants into the aquaculture industry and I thought it would be useful to highlight these, as a guide to new entrants so that they can avoid these errors, and to remind more experienced farmers to duck these mistakes.
1. STOCKING TOO MANY FISH
Surely the most common error made by new (and less new) fish farmers is to stock too many fish into the tank, cage or pond. We want to grow as many fish as possible and wish to maximise return on our investment, so we push the boundaries a little. The result is as predictable as night following day; oxygen levels are compromised resulting in reduced growth, a poor FCR (feed conversion ratio) and high N-compounds as the filters struggle.
Every cage, pond or tank has an optimal density and if you stock more fish than the optimal density dictates, the growth of the fish will be compromised. Some people logic that, by stocking more than the optimal number of fish, although the individual fish mass is decreased, the biomass will increase (due to the greater number of fish to be harvested). The opposite has in fact been shown to be the case: the total biomass decreases if the fish are overstocked. Furthermore, larger fish often command a higher selling price than smaller fish, again favouring the production of fewer, larger fish. A final thought is that if a problem occurs, such as a very hot day impacting ponds or a power failure in a RAS (recirculating aquaculture system), the tank with the higher density of fish will have more demand for oxygen than the tank at a more moderate density.
The lesson: know what the appropriate density is for the infrastructure you farm and avoid the temptation to stock beyond that point.
2. HARVESTING IMPROPERLY
Yep, you know who you are! You go out there on a pretty spring afternoon and over- harvest your bass. You have removed too many pounds of bass into short a period of time and this causes an imbalance between the bass and forage. The result is stunted and overpopulated forage species and a pond full of trotline bait! Remember that a bass filleted at 5 pounds seldom reached 10 pounds. So if your goal is trophy bass harvest selectively but don’t release all the smaller fish you catch. What about you catfish producers?
You may stock heavily and feed heavily, both of which are OK, but then fail to harvest enough fish to keep the total weight of fish present below 1,000 pounds per surface acre during the warm months. The state is set for an oxygen depletion to occur. When you start recognizing and naming individual fish as they come up to feed, its way past time for a fish fry!
3. TOO MANY TANKS; TOO FEW FILTERS
RAS farmers starting out often place too much emphasis on creating lots of tank space to house the fish with the water management, and consequently the filtration system, only receiving a scant afterthought. Adequate mechanical filtration is essential to remove the suspended and settleable solids from the flowing water, and the biological filter must be both large enough and efficient enough to convert all the ammonia to nitrite, and all the nitrite to nitrate. Failure on either side will result in poor water quality, reduced growth, poor FCR and increased disease susceptibility.
The lesson: have the RAS professionally designed to ensure that the filtration system can maintain the target water quality even when the system is fully stocked.
4. TOO MANY WEEDS
It’s easy to think there is “scum”, there is “moss” and everything else is a “weed.” But herbicides and triploid grass carp are not cheap, so make sure you
know what plants you need to control so you can choose the most effective methods. Many pond owners waste lots of cash each year by guessing at the species of weeds they want to control.
The rumor that you can fertilize your weeds to kill them persists throughout Texas and the southeast. It’s true that a proper fertilizer program increases the
phytoplankton and gives the water a greenish hue, which can block out sun and prevent submerged weeds from getting started. However, if the vegetation is already growing before you fertilize, it will effectively compete for the nutrients in the fertilizer and the result may be an increased population of healthy weeds.
5. TOO LITTLE WATER FLOW
Another common mistake in RAS’ is to have an exchange rate that is too slow. Two related concepts are both important here: circulation and exchange rate. Circulation refers to the velocity of the water movement within the tank, generally referring to a circular tank and the water moving around inside the tank. This is important as it keeps the solid wastes in suspension until they exit via the central bottom drain, thereby ensuring that the tank always remains relatively clean. Larger fish tolerate faster circulation, leading to more efficient cleaning, than smaller fish of the same species.
Exchange rate relates the volume of the tank to the volume of water flowing into the tank per hour and is an important calculation as this dilutes the dissolved organics by replacing the water regularly. We have seen that an exchange rate of 1 tank volume per hour is a good basic guide but this needs to be adapted to many variables including the density of fish, species and fish age.
Both circulation and exchange rate are usually achieved simultaneously by pumping water into the fish tank at an angle that creates a circular flow within the tank, carrying the solid and dissolved organic wastes out through the center bottom drain to the filters.
The lesson: know the correct rates for your system and species, and scale the pumping system accordingly.
6. FAILING TO HAVE PH AND TOTAL ALKALINITY TESTED.
This applies only to pond owners whose ponds are on acid soils. Low pH and alkalinity will hamper fish production no matter how much your pond cost to build or how much you spent on your fish. Have a water sample tested and apply agricultural limestone if required.
7. TOO LITTLE AERATION
This goes hand-in-hand with the points above; if there are too many fish in the tank relative to the rate of oxygen replacement oxygen levels will drop, consequently reducing the growth rate of the fish, efficiency of feed usage and increasing vulnerability to disease. In addition, if there is inadequate oxygen (≤4mg/ℓ) then the biofilter bacteria will also fail to efficiently convert ammonia to nitrate.
The lesson: Ensure that there is adequate aeration for the fish and biofilter to function optimally.
8. STOCKING YOUR POND WITH WILD FISH
Many pond owners decide to supplementally stock their ponds with fish from another pond or reservoir. This often results in an imbalance between the forage and sportfish populations, which can lead to poor fishing. Besides, you never know if those wild fish you are bringing in are host to a disease or parasite pathogen. Stick with farm-raised sport and forage fish. You won’t regret it in the long run.
9. USING POOR GENETICS
Tilapia are extremely easy to fish to breed and tilapia farmers are consequently most at fault here. The temptation to grab the first fish you find when your infrastructure is ready to receive fish is great because you want to get farming. However, the most available fish are often inbred and of limited economic value. These fish usually have a slower growth rate and poorer yield (ratio of the fillet to body) than commercial strains.
The maths is simple to do: compare how many fish you can produce from your ponds in 5 years if you use a strain that takes 5 months to reach market mass vs a strain that takes 7 months.
The lesson: Be patient and find the best quality fingerlings you can, both in terms of growth rate and yield.
10. NOT MANAGING THE LIVESTOCK
All too often we find newcomers plan to place fish in their systems in Month 1, leave them there until harvest size and then harvest them for the first time. This strategy is inefficient for several reasons, including, failing to provide an opportunity to remove slow-growing fish, underutilises infrastructure in the early months, fish may not feed well initially as low-density results in vulnerability stress, and it does not group fish according to size so the harvest includes a range of sizes which creates marketing issues.
It is far better to stock the fingerlings into a small container for a limited period – typically 1 or 2 months. They are then harvested, sorted according to size, the slow growers are discarded and the rest are restocked into a larger pond at a reduced number per cubic meter, and given a further period of 1 or 2 months before repeating – harvest, sort and restock.
The lesson: have a plan according to which the tanks, cages or ponds are stocked, harvested. size sorted and restocked, and then work the plan.
11. FAILING TO KEEP HARVEST RECORDS
How are you going to know what to harvest if you don’t know what you have? Even if the barn needs painting, the cows need worming and the pasture needs mowing, you must go fishing and keep catch records to determine the size structures of the species in the pond. This allows you to keep track of which and how may fish should be harvested using Percentage Size Distribution and Relative Weight. And the best thing about harvest records is— they cost you nothing!
12. FEEDING INCORRECTLY
The feed is the fuel that enables the fish to grow. Feed too little and the fish may have fantastic genetics and excellent water quality, but they will lack the fuel that drives their growth. Equally, if you feed too much the fish cannot eat all that is provided, resulting in waste, dirtying of the water and compromising of growth. It is therefore vital to feed the correct amount of feed.
Feed quality is also vital. We have seen in our hatchery that good quality feed results in less size differentiation, much larger fish, greater survival and better water quality than in adjacent tanks being feed poorer quality feed.
The lesson: use high quality feeds only and apply appropriate techniques to ensure adequate feed for excellent growth.
POINTS TO NOTE
Edith Sempebwa Sewali, a fish farmer, advises anyone venturing into fish farming to do the following before they start. Carry out research to know the right place where to get the right quality of fingerlings, where to get affordable feeds and the alternatives as well. Always use the right persons when constructing the ponds. First-time fish farmers should always seek a second opinion from seasoned, successful farmers besides the experts.
When buying fingerlings, one should ensure that they get those, which are at least two months old from the right reputable sources and “seek a guarantee period for replacements in case it is the wrong type or the one other than that requested.
