Factors Affecting Productivity Variables related to the productivity of the system: 1.Fish-associated factors 2.Water-associated factors 3.Pond-associated factors 4.Nutrition-associated factors 5.Management-associated factors

Example: Increase of water temperature by 2 o C 1. 2.The oxygen demand (metabolic rate) increases 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 (NH 4 + ) is generated – Ionized NH 4 + 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 –

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 15 o C and 20 o C Factors Affecting Productivity

Warmwater species Fish whose S.E.T. is generally > 20 o C 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.

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.

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. Factors Affecting Productivity