Parasitic copepods affect morphospace and diet of larvae of a temperate reef fish

Modelling seasonal patterns of larval fish parasitism in two northern nearshore areas in the Humboldt Current System

Macro- and micro-environmental factors modulate parasite loads in fish, determining parasitic abundances, diversity, and interaction dynamics. In this study, seasonal variations in larval ectoparasites on fish larvae in the northern Humboldt Current System (HCS) were evaluated using a delta-gamma generalized linear model to predict their occurrence frequencies. Fish larvae were collected from two nearshore areas during austral spring-summer and autumn-winter. Only five (of 38) larval fish species were parasitized by copepods: Gobiesox marmoratus, Ophiogobius jenynsi, Helcogrammoides cunninghami, Myxodes sp., and Auchenionchus crinitus. A binomial model showed that the presence/absence of parasitized fish larvae varied among the fish species and their larval abundances, while a positive delta-gamma model showed that ectoparasite frequency varied among the seasons and fish species. Seasonal variations in parasitized fish larvae frequency could be associated with host and parasite reproductive processes, which are related to oceanographic features responsible for larval retention and subsequent higher infestation probabilities. Host length was positively correlated with ectoparasite length, suggesting early infection and combined growth until the detachment of the ectoparasite. Our results suggest that infestation patterns in larval fish species can be identified using delta-gamma models and that they respond to local (retention) and high-scale (HCS) processes.

Larval parasitic copepods affect early life history traits of a temperate clingfish

Larval copepods are frequent parasites that infest fish larvae along the Chilean coast. Because these parasites develop on fish during the early development, when their bodies are fragile and in a recent stage, they can affect the fishes' early life history traits (ELHT). The goal of this study was to determine the effect of parasitic copepods on the ELHT of the larvae of the clingfish Gobiesox marmoratus (Teleostei: Gobiesocidae) using otolith microstructure analysis. Ichthyoplankton samples were collected during austral winter (July and August 2012), in the inner shelf waters off Valparaiso Bay, central Chile. A total of 95 non-parasitized larvae (NPL) and 95 parasitized (PL) with copepods were randomly selected for subsequent analyses. Parasitized larvae of G. marmoratus were larger than NPL. The right otolith tended to be larger than the left otolith in the fish larvae, but with a higher asymmetry in PL. The PL showed larger otoliths-at-size than the NPL, particularly in smaller larvae (< 8 mm of standard length, SL). Nonetheless, parasitized larvae larger than 8 mm SL showed the opposite trend that is smaller-at-size otoliths than NPL. The Gompertz models indicated that the asymptotic length of NPL doubled the length of PL; this suggests that parasitic copepods affect the maximum size attained by the PL. In conclusion, parasitic copepods negatively affect the ELHT of G. marmoratus larvae and the greater asymmetry can be attributed to parasitism.

Lunar influences in the diet habits and selectivity of larval clingfish Gobiesox marmoratus

The influence of the lunar cycle on the feeding habits, feeding success and selectivity was tested in situ on larval stages of the clingfish Gobiesox marmoratus (Gobiesocidae). Gobiesox marmoratus larvae and their prey were collected in the water column during the lunar cycle in austral spring 2015 and 2016, in shallow waters (<30 m depth) of El Quisco, central Chile. Feeding incidence was high (80-100%) throughout the moon cycle. The diet was composed of 32 prey items, being gastropod larvae and invertebrate eggs the most important. Prey composition varied among lunar phases with the lowest prey richness during new moon. During 2016, G. marmoratus larvae ingested the lowest number, but the largest prey during new moon. In spring 2015, there were no significant changes in the abundance of each prey taxon in the water column among moon phases, but in spring 2016 there were significant differences in the abundance of cypris and copepod nauplii, particularly between full and new moon. Feeding selectivity index showed that gastropod larvae were positively selected throughout the lunar cycle during spring 2015. In spring 2016, invertebrate eggs were selectively ingested in full moon and third quarter, but at a new moon G. marmoratus larvae selected gastropod larvae. Mean temperature of the water column and its vertical gradient and nocturnal cloud cover influences the feeding success of larval G. marmoratus. Lunar illumination favoured only an increase of richness of prey items. Therefore, nocturnal cloud cover precludes a greater influence of lunar illumination in the larval trophic ecology of this crypto-benthic fish.