Table 3.

List of environmental variables and management practices obtained from Nile tilapia production units between 2012 and 2013 in Yucatán State

Management practices (n = 32)	Low technology farms	Medium to high technology farms
Environmental variables (7)
Fish age (months)	2–4.5	2.5–6.0
Mean annual production (kg)	200–500	1,000–25,000
Water supply	<1 km	>1 km
Number of tanks on the farm	1–4	5–13
Tank capacity (m3)	4–6.5	12–16
Fish density per tank	950–4,500	5,000–10,000
Number of workers	1–2	4–9
Nearby communities	<1 km	>1 km
Fingerlings source	Campeche	Campeche – Tabasco
Type of tanks	Concrete – geomembrane	Concrete – geomembrane
Epidemiological outbreaks	Parasites, bacteria, fungi	Parasites, bacteria
Prophylactic treatments	No	Salt, Crustabay
Quarantine area	No	Yes
Vector presence	pigs, cattle, poultry, dogs and cats	Sometimes dogs
Guardhouse	No	Yes
Footbaths	No use	Yes
Tank cleaning	No disinfection	Virkon, chlorine
Bathroom	Latrine / No use	Bathroom
Disinfection of equipment	No disinfection	Virkon, chlorine
Warehouse	Galley / Lacking	Cement
Drug use	No	Antibiotics
Incineration of organisms	No	Burying and incineration
Education level of workers	No education	Elementary school, sometimes preparatory
Drainage	No drainage	With drainage
Communication	Roadless	With road
Livestock areas	Poultry and pigs	Poultry
Agricultural areas	Yes	Yes
Accumulation of garbage	Yes	No
Accumulation of dead animals	Yes	Sometimes
Water exchange rate	Monthly and fortnightly	Weekly and fortnightly
Water discharge treatment	No	Sometimes
Other land uses	Husbandry and livestock	Sometimes livestock
Nitrates (mg/l)	4.21–7.57	0.10–5.0
Nitrites (mg/l)	0.002–2.97	1.83–3.10
Ammonium (mg/l)	1.85–3.38	0.01–1.68
Salinity (ppt)	0.30–0.70	0.83–2.11
Dissolved oxygen (mg/l)	1.98–7.68	7.78–13.61
Conductivity (μS/cm)	1044–1698	1831–4364
Temperature (T °C)	23.10–31	28.92–32