288 Organic waste recycling: technology and management
Figure 6.14 Observed versus predicted fish weight for septage-fed pond; SD = 1, 5; COD
loadings = 150 kg/(ha-day)
Fish culture and stocking density
Polyculture of fish (such as herbivores and carnivores) is not advisable in waste-
fed ponds because of public health considerations due to direct contact of all
these fish to the wastewater, even though it utilizes all part of the aquatic
environment. It is not practical to design a waste-fed pond to rear different
species of fish because their tolerance levels to low DO are different. Also the
carnivores might predate the herbivores, thus hampering the potential growth of
the herbivores.
Fish sex is an important factor when yield needs to be increased. Due to
genetic reasons, male tilapia generally grows faster than their female
counterparts (Guerrero, 1982). Monosex male culture of tilapias gives faster
growth and eliminated unnecessary reproduction, which can take place during
the culture period. Besides the increased yields, the produced male tilapias
would be of the same size, easier to be harvested and marketed. Monosex
tilapias can be obtained by:
r^2 = 0.98
+ Data from Equation 6.6
Data from experiment 2 of
Edwards et al. (1984)Predicted fish weight (g) +Observed mean fish weight (g) *