People that get a healthy dose of omega-3 fatty acids in their diets may have a reduced risk of heart disease, high blood pressure and strokes, and fish are a major source of these fatty acids. But, what good are omega-3s to the fish themselves?
It turns out that omega-3s may give young fish the boost they need to dart away from predators, leading to greater survival of the vulnerable larvae and potentially larger populations of adults.
Drs. Lee Fuiman and Alfredo Ojanguren from The University of Texas at Austin’s Marine Science Institute discovered this omega-3 advantage studying the larvae of redfish that were raised from adults spawned and managed by biologist Dr. Robert Vega, with the Texas Parks and Wildlife Department. They raised 40 batches of the young redfish over two consecutive years.
Fuiman and Ojanguren measured 16 different aspects of escape responses in the 3-week-old, 8-mm-long larvae to gauge their ability to detect and respond to predators. Fish larvae use escape responses, such as rapid movement away from an attacking predator, to avoid being eaten. The researchers also measured the amount of omega-3s in the eggs from every batch.
The work revealed big differences in escape responses between the two years. Larvae from the second year’s eggs had much greater acceleration than those from the first year, and their escape responses lasted about 50 percent longer. These larvae could cover much greater distances during escape, and this could possibly lead to better chances for their survival in the wild.
Interestingly, there was also a big difference between the two years in the amount of omega-3s in the eggs from which the larvae hatched. The faster second year larvae hatched from eggs that had 25 to 50 percent more of two particular omega-3s than those from the first year.
Fuiman thinks that the omega-3s gave those larvae their boost.
“From what we already know about the effects of omega-3s in humans, these findings make sense – too little of these essential fatty acids can cause deleterious effects,” says Fuiman.
Unlike humans, however, it’s not the fish larva’s diet that is giving them the omega-3 advantage, says Fuiman. They actually receive the advantage through the yolk that their moms put into the eggs.
Fuiman and Ojanguren know this because they fed the redfish larvae a diet that was enriched with fatty acids for about two weeks prior to going through the escape response testing. But this enhanced diet did not help the first-year larvae overcome their original omega-3 deficiency.
In the case of larval fish, it is the mother’s diet a few days or weeks before spawning that most likely determines how much of the omega-3 fatty acids are in the eggs, and ultimately, how well the larvae survive.
“There appears to be a permanent developmental effect of omega-3 deficiency in the eggs, and this effect could lead to greater mortality of larvae,” says Fuiman.
Fuiman says the implications of these findings are important for management of broodstock used in stock enhancement programs and for redfish in nature. “To produce larvae with the best survival skills--those that will grow to catchable size--we need to ensure that the female broodstock receive the right amount of omega 3 fatty acids in their diet during the spawning season,” he says.
Fishes can manufacture a number of fatty acids themselves, but they cannot manufacture the specific omega-3s that appear to be important to the development of good escape responses. They get these omega-3s from the food they eat.
In nature, omega-3s are found more in some animals than others. One of the fatty acids that is essential for good escape responses is abundant in sardines. (There is half as much in squid and about one tenth as much in shrimp.) The quality of larvae produced by redfish may depend in part on the food available to the adults, which can change when they move from offshore waters to the coast during the spawning season in the western Gulf of Mexico. Redfish larval survival may also differ by region of the country, given the variation in the communities of marine organisms that adult redfish consume in these areas.
This article originally appeared in the July/August 2009 issue of CCA Texas' TIDE magazine.
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