lecture 3 factors effecting productivity

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

•


Fish-Associated Factors (intrinsic factors)

Stress response:

• everyday hatchery practices –

• Decreases in circulating ascorbic acid (vitamin C)

• Increase in plasma cortisol


Other fish-associated factors Ammonia-nitrogen:

• Natural byproduct of protein metabolism. • Ammonia (NH4

+) is generated –

• Ionized NH4+ is non-toxic to fish –

•



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.


Environmental Requirements:

Coldwater species•

• Maximal growth rate –

Coolwater species

• S.E.T. is generally between 15oC and 20oC•


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


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


Growth Rate Potential (GRP):

• The maximum growth rate that may be achieve and is measured as increases in length, weight or both.

•


• 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.



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.


Cannibalism: •

• Can be minimized by frequent grading and diligent feeding practices.

Oxygen Uptake:

• Rate of oxygen uptake across the gill lamellar membranes is important



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.


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 -


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.

•


Alkalinity and Hardness

• Hard water (>250mg/l alkalinity)

• Soft water (<100mg/l alkalinity)

•


Contaminants

• Water must be free of municipal, industrial, and agricultural contaminants.

• Natural heavy metals must be below 1 mg/l.

•


Solids

•

• Net results of suspended/settleable solids is generally a reduction in growth rate and increased food conversion rates.


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.


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.


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.


lecture 3 factors effecting productivity

Education

fish factors

waterchemistry factors

dependent onmany factors

fish species

rate of oxygen uptake

water osmolalityiv

maximum growth rate

quantitydissolved oxygen