Browsing by Author "Borski, Russel J."
Book chapterEGT de Jesus-Ayson & RJ Borski - In Technical Reports: Investigations 2007-2009, 2010 - AquaFish Collaborative Research Support Program, Oregon State UniversityIn the Philippines, cage culture of milkfish in marine environments is increasing. The practice uses high stocking densities, with significantly greater inputs of artificial feeds which more often than not, has led to excessive feeding and consequently excessive nutrient loading in receiving waters, exacerbating problems with pollution. These could have contributed to occurrence of periodic fish kills in areas of marine milkfish culture clusters. Sixty percent of milkfish farming expenses are attributable to feed costs. A series of experiments were conducted in an attempt to develop alternative feeding strategies that will reduce feed inputs without compromising growth and resulting production. In the first experiment, growth was compared in milkfish fed daily, on alternate days and on alternate 2-week or 4-week starvation and refeeding cycles in a tank environment provided with flow-through water system. Results show, that milkfish fed on alternate days do not grow as well as milkfish that are fed daily. Feed restriction for 2 weeks followed by 2 weeks of refeeding elicited a compensatory growth response such that average body weight (ABW) of fish was not significantly different from ABW of fish fed daily. Another experiment compared growth of fish given a ration equivalent to 10% of BW (usual practice) or 7.5% of BW. Results show no significant effect on growth or final ABW or biomass in fish fed daily or on 2-week cycles of feed restriction and refeeding. Thus, a lower feeding ration can be given to milkfish without compromising yield. Results of the tank experiments were verified in actual marine cage and brackishwater pond production systems using an initial feeding rate of 7.5% rather than 10% ABW. In the experiment in cages, survival rates between the control fish and the groups subjected to cycles of 2-week starvation followed by 2 weeks of normal feeding were comparable, except for one replicate of the starved-refed group where survival rate was very low (38.78%). After 3 cycles of starvation and refeeding, weight gain in the starved-refed groups were generally lower than in the control groups, which may suggest that small-sized fish cannot adapt very well to periodic starvation. In brackishwater ponds, growth, survival and total biomass at harvest was comparable between milkfish fed daily and those fed on alternate days. Hence, FCR was lower in the milkfish fed on alternate days compared to fish fed daily. On the other hand, survival was very low in fish subjected to 2 cycles of 2 weeks starvation followed by 4 weeks of normal feeding. These results suggest that as in tilapia, alternate day feeding can be adopted to milkfish culture in brackishwater ponds without compromising production while at the same time lowering production cost and environmental impact. Overall, these studies provide two practical strategies, reduced ration size and alternate day feeding, to improve production efficiency of milkfish, the largest finfish aquaculture industry in the Philippines.
Ration reduction, integrated multitrophic aquaculture (milkfish-seaweed-sea cucumber) and value-added products to improve incomes and reduce the ecological footprint of milkfish culture in the Philippines EGT de Jesus-Ayson & RJ Borski - In Technical Reports: Investigations 2009-2011, 2012 - AquaFish Collaborative Research Support Program, Oregon State UniversityIn the Philippines, cage culture of milkfish in marine environments is increasing. The practice uses high stocking densities, with significantly greater inputs of artificial feeds which more often than not, have led to excessive feeding and consequently excessive nutrient loading in receiving waters, exacerbating problems with pollution. These could have contributed to occurrence of periodic fish kills in areas of marine milkfish culture clusters. In marine cage culture, about 80% of variable expenses are attributable to feed costs. Experiments were conducted to compare production characteristics of milkfish fed on alternate days versus those raised on daily feeding in marine cage culture. Fish were fed either daily or every other day using a reduced feed ration at 7.5% of fish biomass at the start of culture down to 3% of fish biomass towards harvest. We showed this ration level was as effective as the industry standard that begins at a rate of 10% average body weight. Morevover, we had previously found that milkfish reared in brackishwater ponds on an alternate day feeding scheme using the reduced ration level produced a 56% cost savings in feed with little impact on total yield relative to fish raised on a daily feeding protocol. In the present study, survival rates (~ 90%) were comparable between the control fish fed daily and groups fed on alternate days in marine cages. Similarly, total harvested biomass of fish in the alternate day and daily feeding groups was similar as was the harvest value, although fish on the alternate day feeding scheme grew slightly less. The amount of feed and the corresponding cost of feeds consumed were significantly lower in stocks that were fed on alternate days compared with those fed daily (P < 0.05). Feed conversion ratio (FCR) was lower in the alternate-day fed group (FCR = 2.46) relative to stocks fed daily (FCR = 3.59). Overall, the results demonstrate that feed costs can be reduced by around 32% in stocks fed on alternate days, which yields an estimated 20-25% improvement in production efficiency relative to raising animals on a daily feeding protocol. Hence, a significant costs savings with reduced impact of nutrient loading in the environment is likely to be realized for farmers who adopt an alternate day feeding scheme in raising milkfish in marine cages.