Morton, B. (1991) Aspects of Predation by Tonna zonatum (PROSOBRANCHIA: TONNOIDEA) Feeding on Holothurians in Hong Kong. J. Moll. Stud. (1991), 57, 11-19.
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Morton, B.
1991
Aspects of Predation by Tonna zonatum (PROSOBRANCHIA: TONNOIDEA) Feeding on Holothurians in Hong Kong
J. Moll. Stud
57: 11-19
Publication
A laboratory-held specimen of Tonna zonatum was
fed holothurian prey over a period of 21 weeks. At
first, the Tonna consumed Holothuria cinerascens,
H. insignis and H. fuscocinerea, but subsequently
consumed only H. leucospilota. Prey size chosen was
in the range 54-200 g total weight with approximately
1 holothurian being eaten each week by extension of
the proboscis. Consumption time was 2-5 minutes and
records of rejection of living prey showed that food is
not cut up in the proboscis by the jaws or the radula
but is engulfed whole.
Holothurians reacted violently to the hunting
Tonna, typically by taking in large quantities of water
to increase in size, particularly in diameter. Holothuna
fuscocinerea 'fled' the predator while H. scabra and H.
leucospilota became buoyant and, writhing, effected
simple 'swimming'.
Calculations of consumption show that this adult
specimen consumed ~2% (wet weight) or ~ 1 % (dry
weight) of its body weight. day"'. This is much lower
than figures for other predatory gastropods, i.e.
~5%.day"'. Analysis of faeces production, correlated
with consumption, suggests a residence time
in the gut of 4 days and an assimilation efficiency of
80.02%. This study and literature data suggest that
the Tonnidae are highly specialized, exclusive, predators
of holothurians.