2. Growth in Finfish
Like all animal and plants, the growth of individuals will vary due
to various genetic and environmental factors. Therefore, even if
the fish are the same age, it is almost impossible to grow all the
fish in your culture units at the same rate and same size.
This difference in size can cause a number of issues in
aquaculture, in many cases the larger individuals may consume
a greater proportion of food or other resources leading to their
faster growth and even more uneven growth and other issues
such as cannablism of smaller individuals. It can also cause
issues when harvesting with uneven size of product for market.
3. Managing growth is important in aquaculture and needs to be monitored regularly so
that corrective measure can be taken if growth is not adequate or uneven. The main
factors affecting growth include:
● Temperature
● Feed
● Stress
● Genetics
● Early maturation (a problem in salmonids, and some tropical species)
● Stocking density
By adjusting these factors we can slow or increase growth to meet production
expectations. In terms of uneven growth, it is common to grade fish regularly to
remove larger or smaller fish to ensure a more evenly sized group.
Growth in Finfish
4. Growth in Finfish
Fish growth can be determined by weight or
length checks, either measure can be used
depending on life stage or type of fish.
Fry/fingerlings or hatchery stock that are small
are often described using length measurements.
However, in grow-out and larger sized fish, we
generally use weight as the indicator
This is discussed in detail in Session 15
Handling and Harvesting of Stock.
5. Temperature Effects on Growth
Temperature is one of the most important controlling factors. Maintaining the optimal
temperature for a species is important for proper metabolic function, health and
growth. Growth and metabolic function is sub-optimal as temperature varies from
optimal; with low temperatures slowing feeding activity and metabolism, and high
temperatures metabolism and growth will increase.
However at elevated temperatures, more oxygen is consumed and more waste by-
products are produced – these may become limiting and compromise growth.
Bacterial and other micro-organism activity will also increase with temperature and
lead to increased risk of opportunistic infection
6. Feed Effects on Growth
Food provides the building blocks for growth and the energy needed for metabolism
and bodily function. The food used must provide all the necessary nutrients for this
and the correct nutrient profile is vital and good quality, well formulated feeds are
critical for good growth and FCR. Some of the things to consider include:
● Different diets are needed for different climatic conditions and temperatures
● Diets are generally species specific and may give poor performance in other
species
● Uneaten food breaks down to reduce water quality reducing growth
● Uneaten or wasted food costs money!
7. Stress Effects on Growth
Species that are widely farmed are generally domesticated and tolerate handling
stress better then new species. Special care may be needed for new aquaculture
species, particularly when using wild broodstock as they have not adapted to
captivity and may stress. Selective breeding programs for high growth rates selects
for fish that tolerate culture stresses better.
Maintaining a good culture environment, as well as adequate nutrition is important in
maintaining a healthy immune system so that the fish is able to fight off any stress.
8. Genetic Effects on Growth
As with other organisms fish growth generally has a genetic component, with growth
rates and size of fish being inheritable. Like most other domestic animals, selective
breeding can be used to breed fish with higher growth rates, larger size or immunity
to disease. Selective breeding is probably most evident in ornamental fish, many of
which have been selectively bred over generations to provide brighter colours and
different body shapes.
However, genetic breeding programs are expensive and can take a long time to
achieve and we are only just beginning work on many species. It should also be
noted culture environment can mask genetic traits and may be difficult to select for.
9. Early Maturation Effects on Growth
Early maturation indicates fish that are
sexually mature at a young age (precocious)
and can have a major impact on growth of
fish and farm productivity. This is a problem
in Salmonids and some overseas species
(eg Tilapia) and result in:
● Poor growth and FCR
● Increased gonad growth (wasted energy)
● Reduced flesh quality
● Changes in body shape, skin and flesh
colour.
● Aggressive behaviour to others.
10. Early Maturation Effects on Growth
There are many ways that early maturation can be managed, these include:
● Triploidy - gametes are manipulated so that there are 3 sets of chromosomes.
This results in fish being sterile but are still able to grow
● Sex reversal or monosex populations – various genetic and chemical means are
used to treat fish so that they change sex and are then used to breed.
● Reducing feeding during critical periods in the production cycle,
● Altered photoperiod or light regimes.
● Lower temperatures decreases spawning behaviour.
11. Stocking Density Effects on Growth
The stocking density(kg fish/m3 of water) of fish can have a significant effect on the
growth of fish. It is still largely a trial and error decision, with a range of factors
effecting management decisions including:
● Culture unit design,
● Water quality and flow rates,
● Temperature range,
● Species and size of fish,
● Feeding regime (ie quality, distribution),
● Staff husbandry skills.
12. Stocking Density Effects on Growth
Overstocking generally leads to poor growth
and highly variable size range due to the
inability to provide sufficient ration to all fish,
poor water quality - particularly DO, and
can lead to stunted growth in ornamentals.
Understocking generally leads to better
growth, but wastes valuable growing space
and feed due to poor feeding response. The
‘art’ of aquaculture is maximising the yield in
terms of growth and the number of fish in
the system.
13. Managing Growth
As can be seen from this discussion,
managing growth of fish is complex.
Factors including the physiology of fish,
water quality, and culture unit
characteristics all need to be considered.
Trial and error may be used to fine tune
densities for particular farms, or seasons.
Improved feeding technology (ie feeds
and distribution) have helped
enormously to overcome these
problems.
14. Managing Growth
Uneven growth or growth dispensation is likely to continue to be a problem for most
farmers. Therefore there is a need to continually fine tune management, and
selective breeding of better performing genetic strains.
Note the vast improvements in chicken and pig farming over the last 20 years
(chicken grown to market size in 6 weeks with FCR better than 1:1). Is Aquaculture
likely to experience the same improvements over next 20 years?
