Revista Chilena de Historia Natural 80 (4): 407-417, 2007
RESEARCH ARTICLE
Changes in mouth morphometrics as related to the diet of Thyrsites atun
(Euphrasen, 1791) from south-central Chile
In several species of carnivorous fishes, as they grow, body size and that of the mouth
are related positively with prey size, however, the number and biomass of preys consumed by the fish don’t present such a clear
pattern. To verify these relationships in the fish Thyrsites atun, a total of 140 individuals were collected from industrial and
semi-industrial landings in south-central Chile. The diet of T. atun was described by means of frequency, number and
weight of preys, which were compared between sub-adult and adult fishes. We also measured mouth morphometry to compare them
with the fish size and prey size. Mouth volume was also calculated to relate it with the number and weight of the ingested preys. Four
prey species were found in their digestive tracts, Euphausia sp., Todarodes filippovae, Strangomera
bentincki and Engraulis ringens, the latter being the most frequent prey (99.9 %). The mouth measures were
dependent of predator body size. Equally, prey size turned out to be dependent of predator size, as well as of the mouth measures.
Also, mouth volume was related positively with predator body size, and the number and the weight of the prey items were correlated
with mouth size and volume. Thyrsites atun feeds in the neritic area on small fishes that live in schools. As size of T.
atun increases so would increase the size of preys, and consequently when the mouth volume increases so does the quantity
and biomass of prey items.
Key words:
Thyrsites atun,
mouth morphometrics, body size, feeding, fish schools
