Lecture 3 factors effecting productivity
Post on 25-Jun-2015
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Example: Increase of water temperature by 2oC 1. 2. The oxygen demand (metabolic rate)
increases3. 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 increases3. 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
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 –
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
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.
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
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.
•
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 rate1. May increase growth rate2. Could have negative impacts on fish if not done within the limits of the system.
Factors Affecting Productivity
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