Measuring and Calculating Growth Performances in cultured Fish/Shellfish

Definition of growth?

• The irreversible increase in size, mass, or cell number of an organism over time

• The net result of energy intake and expenditure (usually influenced by environmental conditions)

Parameters that exhibit growth?

1. Length (long term changes)

2. Weight (biomass or weight changes)

Importance of Measuring Growth?

1. Assessing the health and welfare of aquatic organisms

2. Evaluating the effects of environmental factors and feed quality

3. Applications in aquaculture management, stock assessment, and conservation

Absolute growth

• The simplest and frequently used methods in describing growth is the absolute increase in units measured

• Simple increase in units measured (weight or length)

• Very shallow and insufficient information (as there is no relation to time)

• Unit = cm or g

Absolute growth rate (AGR)

unit = cm/day or g/day

Relative growth rate (RGR)

• The rate of growth of an organism relative to its initial size over a given period, and reported as percentage increase over time

• unit = % in x days

Instantaneous growth rate (IGR)

• A measure of how quickly an organism grows over a short period, expressed as a percentage of its initial size per unit time

IGR new formula

Specific growth rate (SGR)

Rate of growth of an organism as a percentage of its body weight per day

SGR new formula

Factors influencing growth?

1. Intrinsic factors

2. Extrinsic factors

Intrinsic factors?

• Genetic factors: species, strains, and family differences

• Age and life stage (larvae, juveniles, adults)

Extrinsic factors?

• Water temperature, salinity, oxygen levels

• Feed quality and quantity (nutrition)

• Stocking density and habitat quality

Effects of size?

• The growth rate of fish increases at a declining rate with size or weight

• Anabolic and catabolic processes may be paced at different rates in relation to fish weight, with subsequent effect on fish growth

Example of effect of species and genetics

• Grouper and tilapia

• Grouper (carnivorous) has slower growth

• Tilapia (omnivore) has faster growth

• Due to: digestive system, enzyme production (affecting feed digestibility) and metabolism

Effects of food availability

Scope for growth (SFG) is estimated from the difference between the energy gain (energy absorbed) and energy expenditure (loss via respiration and excretion)

Methods of measuring growth?

Morphometric measurements

• Length: total length, fork length, standard length, and body depth

• Weight: whole-body weight, condition factor, and gonadosomatic index

• Body proportions: using equations like the length-weight relationship (LWR) to estimate growth

Tools and techniques for Measuring Growth

Field and Laboratory Measurement Techniques

1. Calipers

2. Scales

3. Rulers and Measuring boards

Calipers

• Used to measure body dimensions

• Digital calipers provide more precise readings compared to manual versions

• Commonly applied in studies assessing growth variations in cultured or wild fish, crustaceans, and shellfish

Scales

• Used to measure the weight or organisms at different growth stages

• Electronic balances provide high accuracy

• Spring scales are more common in field conditions

• Important for determining condition factor, growth rates, biomass estimation

Rulers and Measuring Boards

• Used for standard length, total length, and fork length measurements in fish

• Measuring boards help standardize fish length measurements and minimize handling stress

• Particularly useful for rapid assessments in fisheries fieldwork

Challenges in Measuring Growth

1. Sampling bias

2. Precision and accuracy

3. Environmental variability

Sampling bias

• Handling variation in individual growth rates

• Seasonal effects

• Selective sampling

Precision and accuracy

• Human and instrumental errors

• Repeated measurements on the same fish

• Marking and identification issues

Environmental variability

• Unpredictable events: disease outbreaks, parasite infestations, or harmful algal blooms can stunt fish growth or cause mortalities, altering expected growth patterns

• Fluctuation in water quality: changes in DO levels, salinity, pH, or ammonia concentrations can impact metabolic rates and growth performances

• Nutritional variability: in both aquaculture and wild populations, food availability plays a critical role in growth