biophotonics 11
‘Biophotonics is creating
greater return on investment, as they have a methods to emerge uses laser scanning cytometry.
much better food to weight conversion ratio. Cells are stained with a fluorescent dye, and
breakthrough applications
Triploid fish are also infertile. then stream past a sensor. A laser fluoresces each
in a wide range of sciences’
Inducing triploidy in fish is cheap and simple cell as it passes. Triploid cells have roughly 1.5
– yet another benefit. Fish eggs are shocked times the amount of nuclear material as diploid
into triploidy by sudden changes in either water cells. So by using a DNA-specific stain, triploid
inverted microscope with 103 dry and 403 water pressure or temperature. The drawback of this cells can be made to fluoresce at 1.5 times greater
immersion objectives. Fluorescence was detected technique is that it is not 100 per cent effective. intensity than their diploid cousins.
using 514nm and 633nm laser excitation and Some diploid eggs will remain. Fish farmers Triploid identification by laser scanning
560nm long-pass and 650-710nm band-pass therefore need a method to separate triploid eggs cytometry is typically done with argon-ion lasers.
emission filters for the dyes di-4-ANEPPS and from the remaining diploid. But laser manufacturer Coherent believes that laser
di-4-ANBDQBS, respectively. Depth-correction There are a number of ways of achieving this scanning cytometry is a natural fit for its low cost
of the excitation intensity and photodetector separation. But one of the fastest and most accurate optically pumped semiconductor laser technology.
gain (z-correction function in Zeiss software) was
used to reduce signal intensity variation during
deep (>500µm) scans. Repetitive scans (up to
16) were implemented to reduce the noise in the
images. Whole heart scans were performed using
multiple time series software, with tiled scanning
and subsequent compilation into a single image.
The team claims that its fibre mapping
method combines the advantages of both DTI and
histological methods. It allows non-destructive
myocardial fibre mapping, like DTI. And it has a
spatial resolution of a few microns, as histological
methods do.
Boosting global suppliers of fish
Worldwide demand for fish continues to rise at
a fast pace. Western developed nations import
around 33 million tonnes of fish a year. In Asia,
demand is rising at a rapid pace: countries such
as China have traditionally coveted fish, but had
little access. Now with increasing wealth, Chinese
fishing fleets are being sent out across the Pacific
and into the Indian and Atlantic oceans.
The growing gap between falling wild fish
stocks and rising human demand is being covered
by farming fish, known as aquaculture.
However, normal fish have drawbacks when
farmed. Crowd too many fish into pens and
they respond by becoming stunted. Normal fish
om
typically grow slowly. This slow growth slows
even further in fish farming pens. Genetically
modifying fish – often seen as key to increasing
ooptics.c
yields of farmed fish – has its drawbacks too, as
ectr
.el
farmed fish easily escape into the wild. It is seen as
extremely undesirable to mix genetically modified
www

fish genes with marine wild fish stocks.
One solution to increasing farmed fish
ch 2009
yields and preventing cross contamination with
marine wild fish stocks is triploidy. This involves
genetically modifying the fish so that instead of
carrying the normal double – or diploid – set of f
ebruary/mar

chromosomes, the fish instead carries three.
Triploid fish grow much faster, live longer, put
o
optics
on much more weight, don’t mind overcrowding,
and do not become stunted. They also bring
ectr
el
EOfeb09 pp10-13 Biophotonics.indd 11 17/2/09 16:43:41
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