Factors Affecting Productivity
Variables related to the productivity of the
system:
1.
2.
3.
4.
5.
Fish-associated factors
Water-associated factors
Pond-associated factors
Nutrition-associated factors
Management-associated factors
Factors Affecting Productivity
Example:
Increase of water temperature by 2oC
1.
2. The oxygen demand (metabolic rate)
increases
3.
4.
5. The oxygen-based carrying capacity of
the pond decreases
Factors Affecting Productivity
If pond inflow rate is increased:
1.
2. The water velocity increases
3.
4. The oxygen demand increases
•
Factors Affecting Productivity
Fish-Associated Factors (intrinsic factors)
Stress response:
• everyday hatchery practices –
• Decreases in circulating ascorbic acid
(vitamin C)
• Increase in plasma cortisol
Factors Affecting Productivity
Other fish-associated factors
Ammonia-nitrogen:
• Natural byproduct of protein metabolism.
• Ammonia (NH4+) is generated –
• Ionized NH4+ is non-toxic to fish –
•
Factors Affecting Productivity
Behavior:
•Each fish species has a unique life history and
behavior patterns reflect this.
•Must raise fish under situation that does not
inhibit normal behavior patterns
•Fish can adapt to unnatural situations –
Factors Affecting Productivity
Nutritional Requirements:
• Dietary requirements must be satisfied based
on species needs.
• Nutritionally adequate diets are available for
most salmonids and ictalurids.
Factors Affecting Productivity
Environmental Requirements:
Coldwater species
•
• Maximal growth rate –
Coolwater species
•
•
S.E.T. is generally between 15oC and 20oC
Factors Affecting Productivity
Warmwater species
• Fish whose S.E.T. is generally > 20oC
Thermal Death Point –
• In addition to water temperature, other water
chemistry factors must be maintained within
“no-effect” limits
Factors Affecting Productivity
Product Definition:
• Identification of starting dates and management
processes to be implemented
•
• By working backwards, the start date, number and
size of fish can be determined and implemented as
the product definition
Factors Affecting Productivity
Growth Rate Potential (GRP):
• The maximum growth rate that may be achieve and
is measured as increases in length, weight or both.
•
Factors Affecting Productivity
• Allowable Growth Rate (AGR) is the growth rate
that the system will permit and is dependent on
many factors:
i.
Water temperature
ii.
iii. Water osmolality
iv.
v.
Feed quantity
vi.
Factors Affecting Productivity
Disease History:
•If clinical or subclinical episodes of infectious
and non-infectious disease are experienced
productivity may be affected.
•Direct measurement of such episodes and their
relationship on productivity are difficult.
Factors Affecting Productivity
Length:Weight Relationship: (“condition
factor” K=W(g)/L(mm)3 x 10,000)
•
• For accurate data the condition factor should
be calculated at the end of each growth
period by weighing and measuring
individual fish.
Factors Affecting Productivity
Cannibalism:
•
• Can be minimized by frequent grading and diligent
feeding practices.
Oxygen Uptake:
• Rate of oxygen uptake across the gill lamellar
membranes is important
Factors Affecting Productivity
Oxygen Demand:
•Regulated by the metabolic rate, which is
influenced by factors such as water temperature
and age of animal.
•
Factors Affecting Productivity
Fecal Solids:
•
If allowed to accumulate, a reduction in
growth rate will occur due to:
1. Increases in Biological Oxygen Demand
(B.O.D.)
2. Sestonosis – accumulation of solids and other
detritus on the buccal aspect of the gill rakers
3. Lamellar thickening (hypertrophy or
hyperplasia) resulting from physical irritation
4.
Factors Affecting Productivity
Carbon Dioxide:
•Generated as respiratory by-product.
•
Factors Affecting Productivity
Water-Associated Factors (quality and quantity)
Dissolved Oxygen (DO)
•
• D.O. should generally be > 5mg/l for salmonids.
• Saturation levels -
Factors Affecting Productivity
Nitrite-Nitrogen
• Nitrite is the oxidation product of ammonia
nitrogen and is influenced by the bacteria
Nitrosomonas sp.
• The accepted tolerance level of nitrite is 0.55mg/l.
•
Factors Affecting Productivity
Alkalinity and Hardness
• Hard water (>250mg/l alkalinity)
• Soft water (<100mg/l alkalinity)
•
Factors Affecting Productivity
Contaminants
• Water must be free of municipal, industrial, and
agricultural contaminants.
• Natural heavy metals must be below 1 mg/l.
•
Factors Affecting Productivity
Solids
•
• Net results of suspended/settleable solids is
generally a reduction in growth rate and increased
food conversion rates.
Factors Affecting Productivity
Container-Associated Factors:
• Related to the hydraulic aspects of the system,
such as water velocity and water replacement
time.
• Must provide adequate available dissolved
oxygen for the fish and remove waste products
from the rearing area.
Factors Affecting Productivity
Nutrition-Associated Factors:
• Key factor for optimizing growth and producing a
high quality product.
•
• Aquaculturist has a high degree of control over
the nutrition based factors.
Factors Affecting Productivity
Management-Associated Factors:
• Adjustments to the system or growth cycle that
can be implemented by the culturist.
• Example: increase of feeding rate
1. May increase growth rate
2. Could have negative impacts on fish if not
done within the limits of the system.