WWW.WAS.ORG • 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). Farm managers 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 (CONTINUED ON PAGE 22) 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
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