Wednesday, November 30, 2011

Feeding Tiger Shark Eggs to Japanese Eels - Really?

Scarface by Sasha - fodder for aquaculture?


Although feed made from the eggs of the spiny dogfish Squalus acanthias is currently used to rear larvae of the Japanese eel Anguilla japonica the superiority of these eggs over other shark eggs has not been proven.
Moreover, we need to find new materials of diets for rearing eel larvae if we are to meet future demand for mass production of glass eels. We formulated test diets from the eggs of the tiger shark Galeocerdo cuvier or the gulper shark Centrophorus atromarginatus and used them in feeding experiments. Larvae fed a diet made from tiger shark eggs or gulper shark eggs survived for 21 days after hatching and had adequate growth rates.

However, their survival and growth rates were inferior to those of larvae fed on the diet made from spiny dogfish eggs.

Well, thank God for that!
Tiger Sharks are not oviparous but aplacental viviparous and thus the eggs would have to be harvested from within the animals, meaning that the Sharks would have to be killed. The paper is here and could somebody please have a Japanese friend find out how those eggs have been sourced? Do these findings imply that the future mass production of Eels is going to establish a market for Shark eggs and lead to more targeted mass killing of Sharks?
Aren't Fish eggs bloody good enough?

Howly mackerel - always something new huh!


Chuck said...

Spiny dogfish eggs also have to be harvested from inside the shark. Pretty gruesome source of fish meal.

DaShark said...

Absolutely Chuck!

I just emphasized Tigers as they are a Shark much beloved by divers and as far as I know, not subjected to a major targeted commercial fishery like Spiny Dogfish that are killed for their meat and fins and it now appears, for their eggs as well.

But you're absolutely right of course, Tigers are not more "valuable" than other species and all of those eggs are being harvested from within the Sharks.

Chuck said...

It is kind of an interesting reversal of the usual issues with aquaculture and fish meal. Normally we're worried about aquaculture over-consuming forage fish on the bottom of the food chain, but in this case the "feed" is made out of a predator that would likely eat the eels in the wild. And then of course if they actually decided to start taking them out of tiger sharks... So much for fishing down the food web.

DaShark said...


All very bizarre - why can't they just feed the eggs of the zillions of fish they consume every day...

Oh well, must be an Asian thing - or whatever, we'll likely never find out what went thru their brains in concocting this absurdity.

Anonymous said...

just get this fishermen in boston who caught 10,000 tonnes of sphiny dog fish to save the egg.

they caught n supply daily to four corners restaurabt. also supply to europe the flesh for fish n chip in uk. sold as tock salmon.
thy gutted n throw away tonnes of the eggs.. known as dog fish in boston.