Heteroclarias: High density with exceptional FCR

At target density of 330 kg fish per cubic meter at harvest in a closed Recirculating Aquaculture System (RAS), research suggests the Feed Conversion Ratio (FCR) would likely increase compared to lower densities, estimated at around 0.80. This means fish would convert feed less efficiently due to higher competition and stress at such high densities. It is still an exceptional low score. You need 800 g feed to produce 1 000 g fish.

Key Points

• Research suggests FCR increases at stocking densities above 200 kg/m³ for African catfish in RAS, with estimates around 0.80 at 330 kg/m³.
• It seems likely that at your target density of 330 kg/m³, FCR would be higher than at 200 kg/m³ (around 0.75), due to increased competition and stress.
• The evidence leans toward FCR worsening at very high densities, but an unexpected detail is that FCR can be better at moderate high densities (200 kg/m³) than at lower densities (100 kg/m³, FCR ~0.77).

Background on FCR and Density
FCR measures how much feed is needed per unit of fish weight gain, with lower values being better. At densities above 200 kg/m³, studies show FCR tends to rise, impacting feed efficiency. Your interpretation of 300 kg as 30% assumes fish weight equals water volume, but in reality, fish displace water, which may affect calculations.

FCR at Your Target
Based on a study of African catfish at densities of 100, 200, and 400 kg/m³, FCR was 0.77, 0.75, and 0.83 respectively. At 330 kg/m³, interpolating between 200 and 400 kg/m³, FCR is estimated at about 0.80, higher than at 200 kg/m³. This suggests a 0.05 increase from 0.75, indicating less efficient feed use.

Unexpected Detail
Interestingly, FCR is better at 200 kg/m³ (0.75) than at 100 kg/m³ (0.77), showing a U-shaped curve where moderate high density can optimize feed efficiency before worsening at very high densities like 330 kg/m³.

For more details, check Effects of Stocking Density and Proportional Up-Scaling.

Detailed Analysis of FCR Changes with Stocking Density in African Catfish at High Densities in Closed RAS Systems

This note provides a comprehensive examination of how the Feed Conversion Ratio (FCR) changes with stocking density in African catfish (Clarias gariepinus), particularly at high densities such as the user’s target of 330 kg/m³, in a closed Recirculating Aquaculture System (RAS) with otherwise optimal conditions, such as water temperature. The analysis is grounded in available online resources and aims to address all aspects of the inquiry, offering a professional and detailed perspective.

Background on FCR and Stocking Density

FCR is a critical metric in aquaculture, calculated as the amount of feed given divided by the weight gain of the fish, with a lower FCR indicating better feed efficiency. Stocking density, typically measured in biomass per unit volume (kg/m³) or number of fish per unit area/volume, significantly influences fish growth, welfare, and feed utilization. In RAS, high-density farming is common to maximize production, but it can affect FCR due to competition, stress, and water quality dynamics, even under optimal conditions like maintained water temperature.

The user mentioned a target density of 330 kg fish/m³ and interpreted “over 30% catfish” as densities above 300 kg/m³, based on the assumption that 300 kg fish weighs the same as 300 liters of water, implying water density is 1000 kg/m³, so 30% of 1000 kg is 300 kg/m³. This interpretation suggests that fish biomass is 30% of the water mass, which may be incorrect, as fish displace water and their density in water affects the calculation. However, for this analysis, we proceed with the user’s assumption.

Effect of Stocking Density on FCR in African Catfish

Research suggests that FCR generally worsens (increases) with increasing stocking density, particularly at very high levels, due to increased competition for resources and potential stress. However, the relationship is not always linear, and there may be an optimal density where FCR is minimized. Studies on African catfish in RAS systems provide insights into this dynamic.

A study published in Fishes Effects of Stocking Density, Size, and External Stress on Growth and Welfare of African Catfish (Clarias gariepinus Burchell, 1822) in a Commercial-Scale Recirculating Aquaculture System (RAS) investigated semi-intensive (100 kg/m³), intensive (200 kg/m³), and super-intensive (400 kg/m³) stocking densities over 23 weeks. The FCR for these densities was reported as follows:

This table shows that at 200 kg/m³, FCR was the lowest (0.75), better than at 100 kg/m³ (0.77) and significantly worse at 400 kg/m³ (0.83). This suggests an optimal density around 200 kg/m³ where feed conversion is most efficient, with FCR worsening at very high densities due to poorer growth performance, likely from increased competition and stress, even with optimal water conditions.

Another study, van de Nieuwegiessen et al., 2009, mentioned in Proportional up scaling of African catfish (Clarias gariepinus Burchell, 1822) commercial recirculating aquaculture systems disproportionally affects water quality and fish performance, suggested that stocking densities up to 500 kg/m³ showed no adverse effects on growth, mortality, or welfare indicators, with FCR reported as about 0.80–0.97. However, this is a general range and not specific to 330 kg/m³.

A review paper Effect of stocking density on fish growth and feed conversion ratio: A review concluded that high stocking density can decrease growth and negatively impact FCR, supporting the general trend observed in the African catfish study at 400 kg/m³. The review highlights that stress from overcrowding, even with optimal water quality, can lead to higher FCR due to reduced feed intake efficiency and increased energy expenditure on stress responses.

Interpretation of User’s Target Density and “Over 30% Catfish”

The user’s target is 330 kg fish/m³, and they interpret “over 30% catfish” as densities above 300 kg/m³, based on assuming 300 kg fish equals 300 liters of water, implying water density is 1000 kg/m³, so 30% of 1000 kg is 300 kg/m³. This interpretation suggests that fish biomass is 30% of the water mass, which may be incorrect, as fish displace water and their density in water affects the calculation. However, for this analysis, we proceed with the user’s assumption.

Given this, 330 kg/m³ is above the optimal density of 200 kg/m³ identified in the Fishes study, and closer to the 400 kg/m³ where FCR was 0.83. To estimate FCR at 330 kg/m³, we can interpolate between 200 kg/m³ (FCR 0.75) and 400 kg/m³ (FCR 0.83). The difference in density is 200 kg/m³, and FCR increases by 0.08. Per kg/m³, FCR increases by 0.0004. From 200 to 330 kg/m³, that’s an increase of 130 kg/m³, so FCR would be 0.75 + (130 * 0.0004) = 0.75 + 0.052 = approximately 0.802, or around 0.80.

Alternatively, considering the percentage increase, from 200 to 400 kg/m³, density doubles, and FCR increases by 10.67%. From 200 to 330 kg/m³, density increases by 65%, so FCR might increase by approximately 65% of 0.08, which is 0.052, again giving FCR around 0.802. This estimation suggests FCR at 330 kg/m³ is higher than at 200 kg/m³, indicating worse feed efficiency.

An unexpected detail is that FCR might be better at moderate high densities (200 kg/m³) than at lower densities (100 kg/m³, FCR 0.77), suggesting a U-shaped curve, which might not be immediately obvious given the general expectation that higher density always worsens FCR.

Considerations for Closed RAS with High Intensity and High Density

In a closed RAS with high intensity and high density, water quality parameters like dissolved oxygen, ammonia, and nitrate are tightly controlled, which can mitigate some negative effects of density on FCR. However, physiological stress, as noted in studies like van de Nieuwegiessen et al., 2009, can still increase cortisol levels at higher densities, potentially affecting feed conversion. The Fishes study supports that even with optimal conditions, super-intensive densities (400 kg/m³) lead to higher FCR compared to intensive densities (200 kg/m³).

At the user’s target of 330 kg/m³, which is high density, FCR is likely to be higher than at 200 kg/m³, around 0.80, based on interpolation. This aligns with findings that FCR increases at densities above the optimal point due to competition and stress, even with optimal water temperature.

Conclusion and Recommendations

In conclusion, research suggests FCR increases at high stocking densities above 200 kg/m³ for African catfish in RAS systems, with mixed evidence on exact thresholds. At the user’s target density of 330 kg/m³, FCR would likely be higher than at 200 kg/m³, estimated around 0.80 compared to 0.75, indicating worse feed efficiency. The evidence leans toward FCR worsening due to competition and stress at very high densities, even with optimal conditions. An unexpected detail is that FCR might be better at moderate high densities (200 kg/m³) than at lower densities, showing a U-shaped curve.

This detailed analysis provides a foundation for further research or consultation with aquaculture experts to refine stocking strategies and confirm FCR impacts at specific densities in RAS setups.

Key Citations

• Effects of Stocking Density, Size, and External Stress on Growth and Welfare of African Catfish (Clarias gariepinus Burchell, 1822) in a Commercial-Scale Recirculating Aquaculture System (RAS)
• Proportional up scaling of African catfish (Clarias gariepinus Burchell, 1822) commercial recirculating aquaculture systems disproportionally affects water quality and fish performance
• Effect of stocking density on fish growth and feed conversion ratio: A review