ASSESING THE ROLE OF HOST SIZE AND AGE AS DRIVERS OF THE ABUNDANCE OF LONG-LIVED PARASITES IN FISH STOCK ASSESSMENT STUDIES

BRAICOVICH, PAOLA E.; IENO, ELENA N.; SAEZ, M.; DESPOS, J.; TIMI, JUAN T.

Valencia

Simposio; IX International Symposium on Fish Parasites.; 2015

Universitat de Valencia

There is a general consensus that the most important criterion for an effective parasite marker for stock discrimination is its long residence time in the fish. Long-lived parasites tend to accumulate as fish grow, their abundance depending therefore on both fish size and age. Fish size is used as a surrogate of age, however their functional relationship is not linear and large changes in age do not represent proportional changes in size. Therefore, fish assigned to a given size class can belong to different cohorts, and the sample could be heterogeneous in terms of parasite loads. Consequently, the discernment between the effects of these variables could be essential when comparing samples; however, host age is not usually considered in parasitological studies of stock identification, although it undoubtedly deserves more attention and further research. The size, age (otholith aging), sex, parasite species richness and abundance of Grillotia carvajalregorum, Corynosoma australe and Hysterothylacium deardorffoverstreetorum were recorded for 270 specimens of Percophis brasiliensis caught in the Argentine Sea. The abundances and species richness were modelled using generalized linear mixed models with a negative binomial distribution. An information theory approach, employing a collection of models with different combination of covariates, was followed to identify the optimal set of factors determining the parasite burdens of P. brasiliensis. Results indicated that the covariates length and sex consistently appeared in the most parsimonious models (lowest AIC), suggesting that fish length seems to be a better predictor than age. The biological causes of these patterns are discussed.