Biometric relationships and condition factor of Nile tilapia (Oreochromis niloticus) grown in concrete ponds with groundwater

Abstract This study investigates biometric relationships in Oreochromis niloticus (gray tilapia) reared in controlled pond environments at the Centro de Investigación Piscícola (CINPIS), Universidad Nacional Agraria La Molina (Perú), over a 3-year period (2021–2023). Focusing on total length ( $${L}_{t}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>L</mml:mi> <mml:mi>t</mml:mi> </mml:msub> </mml:math> ), standard length ( $${L}_{s}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>L</mml:mi> <mml:mi>s</mml:mi> </mml:msub> </mml:math> ), height ( $$H$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>H</mml:mi> </mml:math> ), and width ( $$A$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>A</mml:mi> </mml:math> ), we developed models to estimate weight ( $$W$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>W</mml:mi> </mml:math> ) based on these parameters, achieving strong model performances with R 2 values between 0.899 and 0.994. The model using $${L}_{t}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>L</mml:mi> <mml:mi>t</mml:mi> </mml:msub> </mml:math> as a predictor of $$W$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>W</mml:mi> </mml:math> proved most accurate with a mean relative error (MRE) of 11.2%, while models incorporating additional dimensions ( $$H$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>H</mml:mi> </mml:math> and $$A$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>A</mml:mi> </mml:math> ) did not enhance predictive accuracy. Comparative analyses show our model aligns with some studies on tilapia, though variations in L-W relationships due to environmental and breeding conditions are evident. Our results affirm the utility of $${L}_{t}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>L</mml:mi> <mml:mi>t</mml:mi> </mml:msub> </mml:math> in non-invasive biomass estimation for aquaculture, while highlighting the limitations of applying these models universally across different conditions and fish populations. Condition factor ( $$K$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>K</mml:mi> </mml:math> ) and relative condition factor ( $${K}_{r}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>K</mml:mi> <mml:mi>r</mml:mi> </mml:msub> </mml:math> ) analyses further demonstrated stable and optimal growth conditions (mean $$K$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>K</mml:mi> </mml:math> ≈ 1.76; $${K}_{r}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>K</mml:mi> <mml:mi>r</mml:mi> </mml:msub> </mml:math> ≈ 1.01) for tilapia under local culture practices. Accordingly, we propose the L-W relationship $$W= {0.0265L}^{2.8469}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>W</mml:mi> <mml:mo>=</mml:mo> <mml:msup> <mml:mrow> <mml:mn>0.0265</mml:mn> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2.8469</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> for estimating the weight of gray tilapia grown in ponds with groundwater. This study provides a basis for the development of biomass estimation methods based on active acoustics or stereo video.