February 15-18, 2009 Washington State Convention Center Seattle ...

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PLAYING WITH FOOD: EXAMINING REARING DIETS FOR WINTER FLOUNDER
Pseudopleuronectes americanus STOCK ENHANCEMENT THAT OPTIMIZE WEANING
SUCCESS IN THE HATCHERY AND IN THE WILD Pseudopleuronectes americanus STOCK
ENHANCEMENT THAT OPTIMIZE WEANING SUCCESS IN THE HATCHERY AND IN THE
WILD
Michelle L. Walsh*, Elizabeth A. Fairchild, Nathan Rennels, Stacy C. Farina, W. Huntting Howell,
Renee Mercaldo-Allen and Catherine Kuropat
University of New Hampshire
Durham, NH 03824 USA
michelle.walsh@unh.edu
Winter flounder (Pseudopleuronectes americanus) are capable of releasing hundreds of thousands of eggs annually but because
of the vulnerability of the small, early life-history stages, there is high natural mortality, and few survive to maturity. Captively
spawning, rearing, and releasing animals at a size or age beyond this mortality window may enhance natural stocks. A major
challenge of any captive rearing program, whether for aquaculture or stock enhancement, is providing the appropriate diet regimes
during development. Typically marine fish larvae are initially fed live food (e.g. rotifers, Artemia), and then weaned onto
formulated diets as they attain a size or developmental state that supports consumption of these artificial feeds. Weaning occurs
twice for fish that are used for stock enhancement; the second time occurs as they transition from the hatchery feed to natural
live diets once released. This research, which is part of a larger study designed to assess the feasibility of winter flounder stock
enhancement in New Hampshire, aims to identify rearing diets that optimize weaning success in the hatchery and minimize the
effects of subsequent weaning in the wild.
In 4-wk laboratory feeding trials, we analyzed the weaning
success of hatchery-reared, juvenile winter flounder raised
on different diets (both live and formulated) by quantifying
growth, survival, and RNA/DNA condition. Live diets included
late-stage nauplii of brine shrimp (Artemia franciscana), white
worms (Enchytraeus albidus) and burying marine amphipods
(Leptochierus plumulosus). Initial results indicate that fish
reared on live diets exhibit significantly higher growth (Fig. 1)
and survival than those reared on formulated diets (p < 0.05).
RNA/DNA condition was also higher in fish fed live feeds.
Subsequently, we examined the weaning success of these hatchery-reared
fish once released in the wild. In addition to growth
and survival, we determined the onset of feeding post-release,
gut fullness, and gut composition by performing controlled
cage
releases. Fish raised on live diets exhibited higher growth in
the wild than pellet-reared fish. This research provides information
that may promote advances in weaning strategies for stock
enhancement.