Poster: Survey on use of natural food and supplemental feed in milkfish farms on Panay, Philippines

This poster was presented at "Deutscher Tropentag 2000" – International Agricultural Research – A Contribution to Crisis Prevention, October 11-12, 2000, University of Hohenheim

Survey on the use of natural food and supplemental feed in commercial milkfish farms on Panay, Philippines

Christian Lückstädt¹, Ulfert Focken¹, Relicardo Coloso² & Klaus Becker¹
¹Dept. of Animal Nutrition and Aquaculture
Institute for Animal Production
in the Tropics and Subtropics
University of Hohenheim (480b)
70593 Stuttgart, GERMANY ²Southeast Asian Fisheries Development Center (SEAFDEC)
Aquaculture Department
Tigbauan Main Station
5021 Tigbauan, Iloilo, PHILIPPINES

Introduction

The milkfish (Chanos chanos Forsskål; Fig. 1) is the most important cultured fish species in the Philippines. In 1998, more than 156,000 t were produced here, over 91 % of this in brackishwater ponds. A significant part of this production is achieved semi-intensively in commercial fish farms with supplemental feeding. Investigations on the intake of supplemental feed and natural food by milkfish in small experimental ponds showed that only a part of the supplemental feed was taken in directly by the fish. The present study was aimed at finding out the utilization of natural food and supplemental feed in commercial milkfish ponds using different management systems.

Materials & Methods

Pond monitorings were conducted on Panay Island, in two commercial milkfish farms (Fig. 2) using different culture methods (intensive: fed a compound diet with 19 % crude protein content; semi-intensive: used organic fertilizer instead), between October 1996 and August 1998. Samples of up to 5 fish were caught with a cast net at every hour of the day. Fish were measured, weighed and the stomachs removed. The daily diet intake was estimated by microscopic and gravimetric analyses of stomach contents followed by an application of the Elliott & Persson (1978) model.

Results

Growth parameters and stomach content distribution differed significantly as shown in Tab. 1 and 2. Based on analysis with the Elliott & Persson model, the daily rations for the fed system (intensive) and for the fertilized system (semi-intensive) were estimated to be 1.02 % and 0.71 % BME d^-1 respectively. The data suggested a direct consumption of only 12 % of the given compound feed (3.75 % BME d^-1) in the intensive farm, leading to a wastage of fish feed. However, considerable growth rates were achieved without any pelleted diets in the fertilized system.

Table 1: Growth parameters of milkfish for both culture systems
Intensive (feeding) Semi-intensive (fertilizer)

Number of fish 82 50

Condition factor 20.6^a ±1.1 19.8^b ± 1.1

Weight gain [g] 214.7 188.3

Growth rate [g/d] 2.2 2.4

SGR 1.0^b ±0.2 2.0^a ±0.4

MGR 7.3^b ±1.1 11.8^a ±2.3

SGR (%) = (ln final mass - ln initial mass) / days of culture * 100
MGR (g kg^-0.8 d^-1) = (mass gain / [(initial mass^0.8 + final mass^0.8) / 2]) / days of culture

Table 2: Food components in the stomach of milkfish in mg / kg fish⁺
Intensive (feeding) Semi-intensive (fertilizer)

Compound feed 168 ± 217 -

Algae 57^b ±86 123^a ±99

Crustacea 11 ±22 9 ±17

Diatoma 45 ±52 53 ±61

Others 2^b ±3 49^a ±55

Detritus 360 ±490 240 ±160

⁺ stomach content (dry matter) / fish total weight (wet matter)

Values given as mean ± SD. Means in each row not sharing a common small superscript differ significantly at p < 0.05.

Discussion & Conclusions

A positive effect of the semi-intensive management in milkfish culture was observed. Fish grew significantly faster in that type of system as compared to the intensive one. This fast growth rate can be attributed to a well maintained natural food through fertilization. The direct intake of the given feed in the intensive system was low. These results indicate that the quantity of feed provided in the intensive system could be heavily reduced or even abandoned in favour of fertilization, since comparable fish growth rates could be achieved without feeding pelleted diets in the semi-intensive system.

References

Elliott, M. & Persson, L. (1978): The estimation of daily rates of food consumption for fish. Journal of Animal Ecology 47: 977-991.