Are Fish Near Extinction? – 06/30/2014

  • August 20, 2014 at 1:16 am #2388

    Are Fish Near Extinction?
    by Staff Writers
    Tel Aviv, Israel (SPX) Jun 30, 2014

    [MC – Comment – Hmmmm, how did the fish survive for so long with this “biological flaw”? Is there something, maybe metallic and electro-magnetic, making their habitat water more viscous?

    Dr. Holzman based his study on the problematic nature of fish reproduction.

    “An end to seafood by 2050?” “Fish to disappear by 2050?” These
    sensational media Are Fish Near Extinction?s were the result of a 2010
    report by the United Nations Environment Program, declaring that
    over-fishing and pollution had nearly emptied the world’s fish stocks.

    That scarcity portends disaster for over a billion people around the world
    who are dependent on fish for their main source of protein.

    Now, a new study by Dr. Roi Holzman and Victor China of the Department of
    Zoology at Tel Aviv University’s George S. Wise Faculty of Life Sciences
    has uncovered the reason why 90% fish larvae are biologically doomed to
    die mere days after hatching.

    With this understanding of the mechanism that kills off the majority of
    the world’s fish larvae, leaving only a marginal proportion to populate
    the world’s oceans, “We can help find a solution to the looming fish
    crisis in the world,” said Dr. Holzman.

    The research, published in PNASand conducted at the Inter-University
    Institute for Marine Sciences in Eilat, Israel, suggests that
    “hydrodynamic starvation,” or the physical inability to feed due to
    environmental incompatibility, is the reason so many fish larvae perish.

    Survival strategies

    “By focusing on the constraints placed on larvae survival, we have a
    better chance of producing higher quality mariculture,” a specialized
    branch of aquaculture involving the cultivation of marine organisms for
    food and other products in the open ocean, said Dr. Holzman. “If we can
    produce better fish, this will have huge implications for our ability to
    maintain fish populations.”

    Dr. Holzman based his study on the problematic nature of fish
    reproduction. Nearly all fish species reproduce externally – they release
    and abandon their sperm and eggs into the water, providing no parental
    care. The fertilized eggs then hatch in the water within a couple of days
    and the hatching larvae must sustain themselves.

    When attached to a yolk sac (a membranous sac attached to an embryo that
    provides early nourishment in the form of yolk), these premature organisms
    can survive for a period of two or three days, but once the larvae, with
    poorly developed fins and gills, open their mouths, they start dying in

    “We thought, something is going on during this period, in which the
    proportional number of larvae dying is greatest,” said Dr. Holzman. “Our
    goal was to pinpoint the mechanism causing them to die. We saw that even
    under the best controlled conditions, 70% of fish larvae were dying within
    the two weeks known as the ‘critical period,’ when the larvae detach from
    the yolk sac and open their mouths to feed,” said Dr. Holzman. “What was
    going on? We turned to physics as a source of the problem.”

    Eating soup with a fork

    The physical structure of the larvae and their flawed interaction with the
    physical environment provided the answer Dr. Holzman was looking for. Over
    the course of two years, he and doctoral student Victor China observed
    fish larvae at three significant points in their development (at the
    beginning, middle, and end of that “critical period” – eight, 13, and 23
    days old).

    They found that the “stickiness” of the water – the viscosity of the
    surrounding ocean water – was hampering the larvae’s attempts to feed.
    “All that determines the larvae’s feeding ability is viscosity – not age,
    not development. Only their interaction with the surrounding water,” said
    Dr. Holzman.

    “Because the water molecules around you have weak electrical bonds, only a
    thin layer sticks to your skin – a mere millimeter thick. If you’re a
    large organism, you hardly feel it. But if you’re a three-millimeter-sized
    larva, dragging a millimeter of water across your body will prevent you
    from propelling forward to feed. So really, it’s all about larval size,
    and its ability to grow fast and escape the size where it feels the water
    as viscous fluid.”

    The researchers found that in less viscous water, the larvae improved
    their feeding ability. In theory, they can be expected to increase their
    survival rate. “We conclude that hydrodynamic starvation is the reason for
    their dying,” said Dr. Holzman. “Imagine eating soup with a fork – that’s
    what it’s like for these larvae. They’re not developed enough at the
    critical point to adopt the constrained feeding strategy of adult-sized,
    better-developed fish.”

    Armed with this knowledge of the larvae’s biological flaw, the researchers
    are currently patenting a solution to maintain higher survival rates among
    fish larvae populations.


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