When measuring feed quality, some of the parameters to be assessed are pellet water stability, feed palatability and digestibility. Pellet stability measures the ability of a pellet to retain its physical integrity in the water until consumed by the animal. It is very important for slow-eating species, such as shrimp, who nibble on the feed, and, most importantly, to avoid water pollution. In this way, it is desirable that a more water stable, pelleted compound feed is used to feed the farmed species to avoid economical and nutritional wastage and be environmentally friendly. Water stability can be measured in different types of feeds, for example, farm-made mash feed, farm-made pelleted feed, extruded feed, commercial feed etc., by calculating dry matter loss. For such ,feed samples are immersed in water for desired time, salinity and temperature, according to animal culture conditions. Horizontal back and forth motion can be used to provide water movement and pellet agitation. After immersion, all solids are recovered by filtration, dried in oven (103 °C, 24h), cooled and weighed. Pellet stability is calculated as:
In this study, the objective was to compare the water stability of farm-made feed mash and extruded pellets, which are currently used in coastal milkfish Chanos chanos farms in Singapore. Duplicate 2-g samples of farm-made feed mash made into a ball and extruded feed were immersed in seawater (28 ppt) at 28 °C for 15 minutes. Samples were agitated with circular movements every 5 minutes. Solids were filtered and dried for dry matter loss calculation. The farm-made mash feed ball started collapsing in the first 5 minutes and totally collapsed by the end of the study. Extruded feed presented swallowing after 15 minutes in water but shape remained intact. Farm-made feed mash presented 21% dry matter loss, whereas extruded feed lost 9% of dry matter. Further to feed nutrient digestibility, pellet water stability is also very important when it comes to effect of uneaten feed in water quality. Therefore, further studies should assess the effect of feed nutrient leaching in water and the impact in the culture environment.