Several studies have been made in estimating the primary productivity of fish ponds. One of the more important studies in this respect is that of Hepher (1962) who compared the primary production in ponds; at different levels of fertilization. Hepher obtained rates of primary production at different depths in the fish pond. The results obtained by him are included in Fig.10.4. Hepher found that a very high initial fertilization did not result in high primary productivity, but medium level of fertilization, where addition of fertilizers to pond was done every two weeks in smaller quantities were more effective. The productivity depth curves for standard level of fertilization (60 kg superphosphate + 70 kg ammonium sulphate per ha every two weeks) and double this level indicate this (Fig.10.4). Eventhough the double fertilization resulted in higher gross production at the surface total production, considering the whole depth of the pond was higher in pond fertilized with standard fertilization. This has important bearing for fertilization regimes in fish pond. These tests have to be done under existing pond conditions and recommendation made.
Ali (1986) measured depthwise PG in ponds at different times, prior to and after fertilization at Aluu. Ali's results are also presented in Fig.10.4. Ali's values are not as high as those obtained by Hepher (1962) but the effect of time of fertilization on PG is very clear. The results are of importance locally and should be explored further. Ali studied maiden ponds which had not been fully prepared and possibly obtained lower PG values.
Noreiga-Curtis (1979) measured depthwise profile of net primary production and calculated the compensation depth (depth at which R = PN) at different times of the year.
Compensation depth of fish ponds changing with level of primary productivity and standing crop of plankton in Israel (from Noreiga-Curtis, 1979)
g C m-2
cm(R = PN)
crop of plankton dry weight mg/l
|1.3 (2.2)||0.6 (0.6)||Bottom 100(100)||2.0 (1.7)|
|5.3 (5.6)||0.7 (2.3)||60(75)||2.1 (3.1)|
|1.3 (3.5)||5.5 (2.9)||40(50)||1.9 (6.7)|
|4.3 (5.9)||3.5 (3.5)||55(55)||5.6 (10.6)|
Note: Values within and without bracket indicate determinations in 2 separate ponds.
In ponds of 1 m depth the compensation depth ranged between 40 – 60 cm. A fact which comes out from the TableX.1 is that (PN) is related to standing crop of phytoplankton. Oglesby (1977) found that fish yield (FY) can be better correlated with phytoplankton standing crop than with primary productivity. This will be discussed separately under “Plankton”.