World Aquaculture - December 2014

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• WORLD AQUACULTURE • DECEMBER 2014 21
Sludge Management
The perception of most farmers (64 percent) is that sludge does
not accumulate in raceways because it is carried out with the flowing
water. Thirty two percent of surveyed farmers declared that they
remove sludge from their tanks and dispose of it. Two said that they
simply dump it in the river. One farmer collects sludge and uses it to
fertilize agricultural crops.
Farmers allow sludge to accumulate in raceways and discharge it
all at once because this is the least labor and time consuming method.
Most farmers lower raceway water level after harvesting, increase
water flow rate and allow sludge to exit ponds and raceways and flow
into the Assi River. Nearly all (96 percent) of farmers do not gauge
the flow rate of water that runs through their raceways. Continual
sludge removal of sludge is better because sludge accumulation can
cause stress in fish and poor water quality (Cripps and Bergheim
2000). Continual removal of sludge was performed by only 32
percent of surveyed farmers.
Use of Chemicals and Therapeutants
Nearly all (96 percent) of surveyed farmers stated they clean and
sterilize tanks between crops. Potassium permanganate (KMnO4)
was mentioned most often (by 79 percent of farmers) as a sterilization
chemical. Most trout farmers apply potassium permanganate to
their tanks when they lower water levels after harvesting. Salt and
quicklime are other products applied to raceways between crops. Salt
was mentioned by 47 percent of farmers and 23 percent say they use
quicklime for their ponds. Many farmers do not know the difference
between permanganate, salt or quicklime as therapeutants.
To clarify, farmers use chemicals if they thought there was a
need, but generally do not use them. They followed cleaning and
sterilizing protocols mainly because other farmers do so. Some
farmers even use potassium permanganate as a drug and apply it
while fish are cultured. Such a treatment is an approved parasiticide
used elsewhere but flow rate and drug concentration are managed
strictly. Excessive use of potassium permanganate can harm fish and
low dosages are inconsequential to the parasites. In addition, farmers
often treat sick fish with permanganate without knowing if the
disease is viral, bacterial or parasitic.
Drugs used to treat the fish included Avytril (enrofloxacin,
fluorquinolone) and tetracycline, each used by 19 percent of the
farmers. However, those 38 percent are not the only farmers giving
drugs to their fish. Farmers generally do not know the names of the
medicines they use and some declare that they receive drugs them
with no label on the bottles.
A potential catastrophe in the making is farmers treating all
diseases with antibiotics (namely enrofloxacin and oxytetracycline),
without knowing if the disease was bacterial and with disregard
to the possible environmental harm of antibiotics. For instance,
enrofloxacin is not approved by the United States Food and Drug
Administration (Koc et al. 2009) and oxytetracycline inhibits
nitrification, a necessary detoxifying process in natural waters
(Klaver and Matthews 1994). Also, oxytetracycline was found
to be “so stable that a half-life cannot be determined” (Shao
2001). Thus, antibacterial drug residues may remain in ponds and
can be transferred from raceway to raceway and into the Assi
River. Antibiotic residues in cultured fish could adversely affect
consumer health, and indiscriminant antibiotic use can promote the
development of drug-resistant bacteria that may also affect humans
(Grave et al. 1990, Wu 1995, Beardmore et al. 1997, Shao 2001,
Zhang et al. 2010).
“Knowing how to deal with disease outbreaks can mean the
difference between a successful business or going broke,” stated
Cain and Garling (1993). Farmmanagers rarely ask for technical
assistance from experts when there is a disease outbreak. Farm
managers along the Assi River mainly copy practices from other
farmers, without trying to find the scientific explanations behind
them. For instance, when NGOs provided farmers with non-labeled
drug bottles, farmers used those for any symptoms they noticed
on rainbow trout, irrespective of the drug. They know that these
treatments are ineffective and possibly harmful and thus hide the
medications they use. We were unable to obtain a list of drugs
distributed to trout farmers by the local NGO.
An Estimate of Aggregate Ammonia Loading from
Trout Farms
In addition to the farming skills a trout farmer should have,
he/she should also understand the environment. The farmer must
be a biologist and ecologist. He should understand the relationship
between the position of the farm on a stream and water quality
entering the raceways. Aquaculture, similar to any agriculture
practice, can be environmentally unfriendly if not properly managed.
The carrying capacity of any system should be estimated and
production levels of an industry controlled accordingly. There are no
estimates of sustainable trout production quantities for the Lebanese
portion of the Assi River so a preliminary estimate was made. The
estimate is based on farmers’ expectations of overall rainbow trout
production for the 2010 season (2,196 t). Assuming a FCR of 1.3, then
2,196 t of fish requires 2,855 t of feed. The feed used by fish farmers
contains 45 percent protein. For fish feeds containing a high level of
protein, the net protein utilization (NPU) is 40 percent. Hence, total
ammonia nitrogen (TAN) released into the Assi River from 2,855 t
of aquafeed would be:
TAN = (1.0 – NPU) × (protein / 6.25) × 1000
TAN = (1.0 – 0.4) × (0.45 × 2,854.93/ 6.25) × 1000 = 123,300 g
( C O N T I N U E D O N P A G E 2 2 )
TABLE 2. Range of water quality parameters along
the Lebanese portion of the Assi River during
August, September and October of 2012.
WATER PARAMETER RANGE
Conductivity (µs/cm) 303 – 368
Temperature (C) 15.1 – 16.2
Oxygen (mg/L) 7.72 – 9.78
pH 8.0 – 8.2
Alkalinity (mg/L) 200
Hardness (mg/L) 200
Ammonia-N (mg/L) 0.02 – 0.35
Nitrite-N (mg/L) 0.0
Nitrate-N (mg/L) 0.37 – 0.84
Phosphorus (mg/L) 0.06 – 0.18