9.6 Organically Farmed Fish
Intensive aquaculture systems are aimed to produce high fish densities in order to
increase the productivity. However, reduction on feed intake and fish growth is
caused by earlier fish reproduction. This is true when we are talking about Tilapia
(Oreochromis niloticus L.). This affects the final yield and therefore the farmer
economic income. This problem can be reduced via male sexual induction
immediately after the eggs eclosion. Steroid hormones, steroid analogs, or nonsteroid compounds have been widely used in male sex reversal of various tilapia
species. The percentage of sex-reversed males depends mainly on the type of
hormones dose, timing and duration of administration, fish species, and size/age of
larvae. These practices have big advantages because the fast fish growth allows us
to obtain a more profitable production and increase the farmer profit (El-Sayed
2006). Aquaculture activity recently has adopted a new perspective called
‘‘Responsible Aquaculture,’’ which states that farmers should know the quality of
wastewater discharged into rivers or seas. However, in México this is not possible,
because most of the farmers work in rural conditions, so they ignore the levels in
water and its effect in other species (Soto-Zarazúa et al. 2012). Elimination of
hormones, organically fish production, has generated some disadvantages on
production such as; low rates of specific growth, mixed culture (male:female), and
as the final result, increase in cost. The low rate of specific growth is a big problem
for aquaculture because it implies a long time for harvest, 3 or 4 months adds.
During this time, farmers need to invest in fishmeal, water, space. Besides,
organically farmed fish have nutritional fishmeal requirements for which acceptable organic alternatives are not currently available. Then, a lot of research needs
to be made on this topic. Fish culture under greenhouse has been probed in order to
increase production without hormones. The result showed that it is possible to
increase the specific growth of fish on greenhouse culture but two problems were
founded: (1) High production on algae and (2) alteration on metabolism.
9.6.1 High Production on Algae
In an experiment conducted under greenhouse conditions environmental temperature variation was between 5 and 40 °C, and temperature inside the tanks shows a
variation of 10 °C, between 20 and 30 °C. Those are recommended range for
Tilapia culture (Timmons et al. 2002). So it can be said that cultivation under
greenhouse diminish the effect of this factor and is helpful tool for water temperature control. However, this range of temperature is a nice condition for algae;
as a consequence, a high growth was found inside the tanks. During the day, a
saturation of dissolved oxygen is reached, but during the night the oxygen
decreases leaving fish in hypoxia conditions, Fig. 9.2 shows some days in the
production cycle mortality of 100 % was found in many tanks.
282
G. M. Soto-Zarazúa et al.
Intensive aquaculture systems are aimed to produce high fish densities in order to
increase the productivity. However, reduction on feed intake and fish growth is
caused by earlier fish reproduction. This is true when we are talking about Tilapia
(Oreochromis niloticus L.). This affects the final yield and therefore the farmer
economic income. This problem can be reduced via male sexual induction
immediately after the eggs eclosion. Steroid hormones, steroid analogs, or nonsteroid compounds have been widely used in male sex reversal of various tilapia
species. The percentage of sex-reversed males depends mainly on the type of
hormones dose, timing and duration of administration, fish species, and size/age of
larvae. These practices have big advantages because the fast fish growth allows us
to obtain a more profitable production and increase the farmer profit (El-Sayed
2006). Aquaculture activity recently has adopted a new perspective called
‘‘Responsible Aquaculture,’’ which states that farmers should know the quality of
wastewater discharged into rivers or seas. However, in México this is not possible,
because most of the farmers work in rural conditions, so they ignore the levels in
water and its effect in other species (Soto-Zarazúa et al. 2012). Elimination of
hormones, organically fish production, has generated some disadvantages on
production such as; low rates of specific growth, mixed culture (male:female), and
as the final result, increase in cost. The low rate of specific growth is a big problem
for aquaculture because it implies a long time for harvest, 3 or 4 months adds.
During this time, farmers need to invest in fishmeal, water, space. Besides,
organically farmed fish have nutritional fishmeal requirements for which acceptable organic alternatives are not currently available. Then, a lot of research needs
to be made on this topic. Fish culture under greenhouse has been probed in order to
increase production without hormones. The result showed that it is possible to
increase the specific growth of fish on greenhouse culture but two problems were
founded: (1) High production on algae and (2) alteration on metabolism.
9.6.1 High Production on Algae
In an experiment conducted under greenhouse conditions environmental temperature variation was between 5 and 40 °C, and temperature inside the tanks shows a
variation of 10 °C, between 20 and 30 °C. Those are recommended range for
Tilapia culture (Timmons et al. 2002). So it can be said that cultivation under
greenhouse diminish the effect of this factor and is helpful tool for water temperature control. However, this range of temperature is a nice condition for algae;
as a consequence, a high growth was found inside the tanks. During the day, a
saturation of dissolved oxygen is reached, but during the night the oxygen
decreases leaving fish in hypoxia conditions, Fig. 9.2 shows some days in the
production cycle mortality of 100 % was found in many tanks.
282
G. M. Soto-Zarazúa et al.