Alternate bangus feeding lessens production costFriday, June 29, 2012 05:27 AM Views : 2011Paul M. Icamina
TIGBAUAN, Iloilo – Milkfish grows just as well when fed four times every other day – instead of three times daily.
Reducing the frequency and amount of feeding significantly lowers the feed cost, now about 60 percent of milkfish farming expenses, said Dr. Evelyn Grace T. de Jesus-Ayson of the Southeast Asian Fisheries Development Center (SEAFDEC) Aquaculture Department.
It lessens as well the feed residues that litter the bottom of bangus farms, she added.
"Milkfish cage culture in marine environments is increasing in the Philippines," she said in an interview. "The practice uses high stocking densities, with greater inputs of artificial feeds which, more often than not, has led to excessive feeding."
Excessive feeding leaves a lot of nutrient residues in the waters, causing pollution problems that contribute to periodic milkfish kills.
Ayson has just finished a study on how to increase rural incomes by reducing feed for milkfish raised – together with seaweeds and sea cucumbers – in sea cages.
Feeding in sea cages on alternate days reduced the feed from about 7.5 percent of milkfish weight at the start of culture to 3 percent towards harvest when the average weight is 350 grams to 400 grams per bangus.
The survival rates were the same when compared to milkfish fed daily.
Although there were more bigger fish in the groups fed daily than in those fed on alternate days, body weight at harvest was comparable between the two groups.
Expectedly, fish fed daily consumed more feeds and thus had higher feed conversion ratio compared to fish fed on alternate days. The feed conversion ratio is the amount of feed needed to gain weight; it reflects feed efficiency.
In conventional practice, milkfish are fed daily at levels starting from 10 percent of body weight depending on fish size. Ayson's study found that reducing the initial feeding rates from 10 percent to 7.5 percent body weight produces similar growth rates.
Previous research found that alternate feeding worked in fishponds, and cheaper by 50 percent. This time, the study showed that similar cost savings are possible in production-scale sea cages without compromising yields.
Trial in sea cages at SEAFDEC's marine station in Guimaras involved 2,500 milkfish fingerlings stocked in 5-by-5-by-3-meter cages, with a stocking density of 33 fish per cubic meter.
Milkfish stocks in three of the cages were fed daily following the recommended daily feeding rate; stocks in the three other cages were fed the same daily feeding schedule but only on alternate days.
The researchers' previous studies at a daily feeding rate of 7.5 percent average body weight was used instead of the standard industry rate of 10 percent average body weight.
Results showed that the survival of milkfish was comparable and averaged around 90 percent in stocks that were fed daily and those fed on alternate days.
The weight and the commercial value of the harvested milkfish were similar for both groups.
Perhaps more important, Ayson said, the reduced amount and cost of feed consumed when feeding on alternate days meant savings of up to a third (32.94 percent) of the feed cost when milkfish is fed every day.
"In highly intensive mariculture systems, feed cost can constitute up to 80 percent of production cost, and we have shown that an alternate day feeding strategy can reduce these costs by as much as 32 percent," she said.
"This translates up to 25 percent savings in milkfish production costs even with a slight delay in harvest time," she said.
Overall, the water and sediment quality were better in the experimental areas where milkfish was fed on alternate days.
The new feeding protocols makes it possible to attain the twin objectives of reduced feed cost and lesser pollution.