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January | February 2012

Feature title: The effects of dissolved oxygen on fish growth in aquaculture

The International magazine for the aquaculture feed industry

Commercial aquaculture is growing worldwide except in Africa where production is still low. With fisheries reaching a

stagnating phase, the world and more so Africa will have to look to aquaculture in the future to provide fish products that will likely be needed. In view of this, a study on water quality management was done which specifically looked at the effects of dissolved oxygen saturation on fish growth. The study was done through a review of literature and a case study using Atlantic halibut. In the case study, halibut of 20-50 g in weight were reared in replicate at 60 percent, 80 percent, 100 percent, 120 percent and 140 percent oxygen saturation levels in a tank recirculation system.

The effect of oxygen saturation levels on growth and feed conversion ratios were taken after two weeks. The results showed that oxygen saturation level had a positive effect on the growth and feed conversion ratio when it was set at 80 percent to 120 percent saturation. At 140 percent the growth was slightly lower and the feed

conversion ratio was higher at 60 percent and 140 percent compared to the other groups. The conclusion was that oxygen saturation level has an effect on growth and feed conversion ratios of fish, and in the case of Atlantic halibut, the growth rate is higher when the oxygen level is between 80 percent and 120 percent. The feed conversion ratio for halibut was lower at 120 percent oxygen saturation.

Gas exchange and oxygen concentration in water

Oxygen as a gas has a low solubility in water. In addition, the amount of oxygen contained in water varies with temperature and

salinity in a predictable manner. Less oxygen can be held in fully air-sat-urated warm seawater than fully air-saturated cold freshwater. While the oxygen content of the water sets the absolute availability of oxygen in the water, it is the oxygen partial pressure gradient that determines how rapidly oxygen can move from the water into the fish’s blood to support its metabolic rate.

This is because oxygen moves by diffusion across the gills of fish. According to Fick’s law of diffusion, the gill area determines the rate of diffusion of oxygen across the gills, the diffusion distance across the gill epithelia, the diffusion constant and the difference in partial pressure of oxy-gen across the gills (Crampton et al. 2003).

Consequently, partial pressure of oxygen is the most appropriate term for expressing oxygen levels in aquaculture water.

However, oxygen concentration is the more commonly used term and, for a

given temperature and salinity, the par tial pressure of oxygen and oxygen content in water are linearly related. Another suit-able method for expressing oxygen levels in aquaculture is percent air saturation (often reduced to just percent satura-

The effects of dissolved oxygen on fish growth in aquacultureby Yovita John Mallya, Kingolwira National Fish Farming Centre Fisheries Division, Ministry of Natural Resources and Tourism, Tanzania

"The effect of oxygen saturation levels

on growth and feed conversion ratios

were taken after two weeks. The results

showed that oxygen saturation level

had a positive effect on the growth

and feed conversion ratio when it

was set at 80% to 120% saturation"

Consequently, partial pressure of oxygen is the most appropriate term for expressing oxygen levels in aquaculture water.

However, oxygen concentration is the more commonly used term and, for a

The effects of dissolved oxygen on fish growth in aquaculture

10 | InternatIonal AquAFeed | January-February 2012

FEATURE

January-February 2012 | InternatIonal AquAFeed | 11

Figure 1

Figure 2: Diagram showing the structure for respiration (gas exchange) in fish. (Source: Microsoft Encarta.1993-2002. www.kwic.com 2008-02-08)

IAF12.01.indd 10 10/01/2012 15:55

tion), which is directly propor tional to the par tial pressure and is repor ted on most oxygen probes that have built in algorithms for temperature and salin-ity (Bergheim et al. 2006). In this study percent saturation was used.

Oxygen uptake in and carbon dioxide release from the fish

During respiration fish, like other animals, take in oxygen and give out carbon dioxide. The process is done by using gills in almost all fish although some can also use the skin and some have lung like structures used in addition to gills. When a fish respires, a pres-surised gulp of water flows from the mouth into a gill chamber on each side of the head. Gills themselves, located in gill clefts within the gill chambers, consist of fleshy, sheet like filaments transected by extensions called lamellae. As water flows across the gills, the oxygen within them diffuses into blood cir-culating through vessels in the filaments and lamellae. Simultaneously, carbon dioxide in the fish’s bloodstream diffuses into the water and is carried out of the body (see Figure 1).

Function of fish gillsFor most fish species gills work by a

unidirectional flow of water over the epithelial surface of the gill, where the transfer of gases occurs (O2 in, CO2 out). The reason for this unidirectional flow of water is the energetic nature of the system. The energy that would be required to move water into and out of a respiratory organ would be much more than that used to move air because water holds low oxygen due to its low solubility (Groot et al. 1995). The blood flowing just under the epithelial gill tissue usually moves in a counter current flow to that of the water moving over it.

This allows for most of the O2 to be taken in by the blood because the diffusion gradient is kept high by the blood picking up

oxygen as it moves along, but always coming into contact with water that has a higher O2 content. The blood receiv-ing the O2 continues to pick up O2 as it moves along because fresh water is being washed over the epithelial lining of the gills (Jobling 1995). By doing so, the fish ventilate the gills while also taking in oxygen and releasing carbon dioxide (Groot et al. 1995).

However there are two ways fish ventilate their gills: buccal/opercula pumping (active ventilation) and ram ventilation (passive ventilation). In buccal/opercula ventilation the fish pull in water through the mouth (buccal chamber) and push it over the gills and out of the opercula chamber (where the gills are housed). At this time the pressure in the buccal chamber is kept higher than the pres-sure in the opercula chamber so as to allow the fresh water to be constantly flushed over the gills.

In ram ventilation, a fish swims with its mouth open, allowing water to wash over the gills. This method of ventilation is common to fast moving fish, and it enables tuna to keep enough oxygen going to the gill surface while swimming at high speed (Boyd and Tucker 1998). During this time the oxygen is absorbed into the blood while carbon dioxide diffuses out of the blood to the water.

Effect of oxygen on fish growth

Oxygen is impor tant in respiration and metabolism processes in any animal. In fish, the metabolic rate is highly affected by the concentration of oxygen in the rearing environment. As the dissolved oxygen concentra-tion decreases, respiration and feeding activities also decrease. As a result, the

10 | InternatIonal AquAFeed | January-February 2012 January-February 2012 | InternatIonal AquAFeed | 11

FEATURE

IAF12.01.indd 11 10/01/2012 15:55

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growth rate is reduced and the possibility of a disease attack is increased. However, fish is not able to assimilate the food consumed when DO is low (Tom 1998). Overall health and physiological conditions are best if the dissolved oxygen is kept closer to saturation. When the levels are lower than those mentioned above, the growth of the fish can be highly affected by an increase in stress, tissue hypoxia, and a decrease in swimming activities and reduction in immunity to diseases.

However, there is a need to maintain the level of dissolved oxygen at the

saturation level which will not affect its physiological or metabolic activities, so as to have high production in any culture system (Wedemeyer 1996). More than that, one has to keep in mind that the oxygen level requirement depends on the species, but also on fish size and activ-ity of the fish. According to Tom (1998) oxygen require-ments per unit weight of fish significantly decline with increasing individual weight.

In carp this reduction may be expressed by the following ratios: yearling = 1, two-year-old carp = 0.5–0.7, marketable carp = 0.3–0.4. Significant dif-ferences in oxygen demand are also found for different species. Using a coefficient of 1 to express the oxygen requirement of common carp, the comparative values for some other species are as follows: trout 2.83, peled 2.20, pike perch 1.76, roach 1.51, sturgeon 1.50, perch 1.46, bream 1.41, pike 1.10, eel 0.83, and tench 0.83.

Growth There was no significant difference in

growth rate of the Atlantic halibut reared at different oxygen saturation levels (Figure 3) during the first period (SGR1). However, there was a significant difference (p<0.02) in the growth rate of the fish during the second period (SGR2). Then the SGR of fish reared at 100 percent saturation was significantly higher than that of fish reared at either 60 percent or 140 percent saturation.

The results of the experiment under different oxygen levels clearly showed that the level of oxygen saturation affects growth. During the second period the SGR was highest at 100 percent saturation. The best FCR was obtained in the groups with the highest growth rate although there was no significant difference in FCR of fish reared at different oxygen saturation levels. The growth of other species of fish is also affected by oxygen saturation such as tilapia (Tsadik and Kutty 1987) and Atlantic salmon (Crampton et al. 2003, Seymour et al. 1992, Forsberg and Bergheim 1996). The growth of Atlantic halibut and Atlantic salmon increases with increasing saturation up to 100 percent saturation. However, these species appear to be more sensitive to oxygen saturation than tilapia ■

12 | InternatIonal AquAFeed | January-February 2012

FEATURE

Figure 3: The graph showing the specific growth rate (SGR) of Atlantic halibut reared at different oxygen saturation levels

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12 | InternatIonal AquAFeed | January-February 2012

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4 | InternatIonal AquAFeed | January-February 2012 January-February 2012 | InternatIonal AquAFeed | 5

Aqua News

IAF12.01.indd 5 10/01/2012 15:54

growth rate is reduced and the possibility of a disease attack is increased. However, fish is not able to assimilate the food consumed when DO is low (Tom 1998). Overall health and physiological conditions are best if the dissolved oxygen is kept closer to saturation. When the levels are lower than those mentioned above, the growth of the fish can be highly affected by an increase in stress, tissue hypoxia, and a decrease in swimming activities and reduction in immunity to diseases.

However, there is a need to maintain the level of dissolved oxygen at the

saturation level which will not affect its physiological or metabolic activities, so as to have high production in any culture system (Wedemeyer 1996). More than that, one has to keep in mind that the oxygen level requirement depends on the species, but also on fish size and activ-ity of the fish. According to Tom (1998) oxygen require-ments per unit weight of fish significantly decline with increasing individual weight.

In carp this reduction may be expressed by the following ratios: yearling = 1, two-year-old carp = 0.5–0.7, marketable carp = 0.3–0.4. Significant dif-ferences in oxygen demand are also found for different species. Using a coefficient of 1 to express the oxygen requirement of common carp, the comparative values for some other species are as follows: trout 2.83, peled 2.20, pike perch 1.76, roach 1.51, sturgeon 1.50, perch 1.46, bream 1.41, pike 1.10, eel 0.83, and tench 0.83.

Growth There was no significant difference in

growth rate of the Atlantic halibut reared at different oxygen saturation levels (Figure 3) during the first period (SGR1). However, there was a significant difference (p<0.02) in the growth rate of the fish during the second period (SGR2). Then the SGR of fish reared at 100 percent saturation was significantly higher than that of fish reared at either 60 percent or 140 percent saturation.

The results of the experiment under different oxygen levels clearly showed that the level of oxygen saturation affects growth. During the second period the SGR was highest at 100 percent saturation. The best FCR was obtained in the groups with the highest growth rate although there was no significant difference in FCR of fish reared at different oxygen saturation levels. The growth of other species of fish is also affected by oxygen saturation such as tilapia (Tsadik and Kutty 1987) and Atlantic salmon (Crampton et al. 2003, Seymour et al. 1992, Forsberg and Bergheim 1996). The growth of Atlantic halibut and Atlantic salmon increases with increasing saturation up to 100 percent saturation. However, these species appear to be more sensitive to oxygen saturation than tilapia ■

12 | InternatIonal AquAFeed | January-February 2012

FEATURE

Figure 3: The graph showing the specific growth rate (SGR) of Atlantic halibut reared at different oxygen saturation levels

No hollow spaces | No cross contaminationExcellent cleaning access | Filtered air inletTemperature control | Moisture control | Cleaning in Place

C L E A N C O N T R O L

Swivel Valve Cooler MkII

c o o l a n d d r y

clean and lean

info@geelencounterflow.com

www.geelencounterflow.com

T +31-475-592315

Geelen Counterflow Holland / USA / Argentina / China

Are you a Perendale bookworm?Perendale Publishers Ltd, the publishers of Grain & Feed MiIling Technology and International Aquafeed, has set up an online Amazon-based ‘Book Shop’ that lets you browse a wide range of recently-published reports and books on related topics. You can now read an extended review before making your selection and purchasing directly from Amazon.

We will undertake to put forward for your consideration the most recent publications and as a result become a reference point for your reading and research.

Of course you will be charged for any books purchased, but you will be dealing directly with Amazon, which has a world-class ordering/payment gateway, packaging and mailing service.

IAF12.01.indd 12 10/01/2012 15:55

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Volume 15 I s sue 1 2 012

the international magazine for the aquaculture feed industry

The effects of dissolved oxygen on fish growth in aquaculture

On-farm feed management practices– for three Indian major carp species in Andhra Pradesh, India

Oxygenation in aquaculture

Developing a plant-based diet- for Cobia Rachycentron canadum

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