the popularity of omega in particular is the source of a structural change in the ratio of these two prices since the resulting ratio is assumed to be maintained over the mediumterm except in the years where the el nino phenomenon occurs for individual fishery commodities price volatility could be more pronounced due to supply swings caused by changes in catch quotas disease outbreaks in the aquaculture sector for example as the one affecting shrimps production in mexico and thailand at present as well as fluctuations in feed costs this is about higher than in the base period but it represents a slower annual growth compared to the previous decade versus