Lernanthropus kroyeri (Van Beneden and Hesse 1851) parasitic Copepoda (Siphonostomatoidae, Lernanthropidae) of European cultured sea bass Dicentrarchus labrax (Linnaeus 1758) from Corsica: ecological and morphological study

Molecular characterization of Lernathropus kroyeri from intensive aquaculture and pathophysiology of infested sea bass

The copepod Lernathropus kroyeri constitutes one of the major parasites for the Mediterranean aquaculture, infesting the sea bass Dicentrarchus labrax causing thus disruptions of growth performance and occasionally mortalities. Despite the large spread and the high frequency of this parasite in mariculture farms of Eastern Mediterranean, L. kroyeri genetic profile from aquaculture as well as the pathophysiological response of D. labrax have not been studied so far. Keeping this in mind, in the present study we investigated the L. kroyeri infestation on D. labrax from two farms in Greece, examining both healthy and heavy parasitized individuals. Assays included histopathology, phylogenetic reconstruction of the parasite and physiological response of the fish by the means of antioxidant, inflammatory metabolic and stress related gene expression analysis at both mRNA and protein levels. Genetic analysis indicated that L. kroyeri composes a monophyletic group, highly phylogenetically distant from other congeneric groups. Heavy infested D. labrax witnessed a significantly increased immune response that further led to oxidative stress and metabolic alterations. Overall, our results demonstrate the, seasonally independent, high infestation of this parasitic copepods, which continue to affect Mediterranean intensive aquaculture systems.

Parasitic copepod (Lernanthropus kroyeri) on caged sea bass (Dicentrarchus labrax): An estimation of abundance and internal infestation pressure

Infestation by parasitic copepods is a substantial problem in the cage culture of European sea bass (Dicentrarchus labrax). The Copepoda parasite, Lernanthropus kroyeri (Lernanthropidae), is one of the threats to the mariculture of sea bass. In the present study, we evaluated the data of abundance for L. kroyeri pre-adults and adult males (PAAM) and ovigerous adult females (AF_o ) to estimate the internal infection pressure (IIP) in the same cage environment. The sea bass infested by L. kroyeri was collected from grow-out sea cages located in Gulluk Bay (Turkey) in September and October 2019. Mean fish weight and length of sea bass were 75.79 ± 1.66 g and 21.40 ± 0.56 cm, respectively. The fixed lag method was used to predict the abundance of L. kroyeri adult females. The overall prevalence of L. kroyeri was 60%. The mean abundance of PAAM and AF_o varied from 0.8 ± 0.24 to 2.5 ± 0.67 and 2.9 ± 0.40 to 4.3 ± 0.55, respectively. The abundance of AF was strongly correlated with PAAM. The pattern of AF_o and PAAM was interpreted as an indication of the continuous infestation of L. kroyeri on sea bass. Our results showed that the correlation of AF_o abundance for five consecutive weeks was significant, representing the main determinative factor for the continuity of the parasitic load. In our approach, internal infestation pressure is the quantitative estimation of the potential infective copepodids, which are mainly characterized by AF abundance and the prevalence. We predicted that the internal infestation pressure could be high, even exceeding the 50.000 × 10⁶ potential infective copepodids for one sea cage with the fish density of 20 sea bass/m³ .

Influence of season and site location on European cultured sea bass parasites in Corsican fish farms using indicator species analysis (IndVal)

The parasites of 536 European sea bass, Dicentrarchus labrax, were studied between January 2012 and December 2013 in six Corsican fish farms. The indicator value (IndVal) method, which combines measures of fidelity and specificity, has been used in this study. Because of its resilience to changes in abundance, IndVal is a particularly effective tool for ecological bioindicator. The IndVal method showed how season can influence the occurrence of parasite species in cultured sea bass and also identified parasites as bioindicators relative to fish farm location. The combination of specificity and fidelity highlighted several parasite species as significant indicators. A randomization test identified five parasite species as having a significant indicator value for season (the monogenean Diplectanum aequans; the copepods Lernanthropus kroyeri and Caligus minimus; the isopod Ceratothoa oestroides, and the myxosporidian Ceratomyxa labracis). If gills parasites are compared, they can be seen to be indicator species for two different seasons. The only Monogenea species D. aequans had fidelity and specificity more pronounced in winter, whereas both copepod species and the Isopoda revealed highest rates of infestation corresponding with an increase of water temperature. Four species have a significant indicator value for site location (D. aequans, L. kroyeri, C. minimus, and C. oestroides). The fact that the farm 6 was isolated on the east coast of Corsica may not have allowed the parasite to infect other farms. The presence of copepods on a single farm can also be explained according to salinity variations. Data for species composition and infection levels should help to improve the monitoring and management of parasitism in cultured sea bass populations.

The effects of a parasitic copepod on the recent larval growth of a fish inhabiting rocky coasts

Parasites can infect larval, juvenile or adult marine fishes; however, the effects of parasites on the growth and condition of fish larvae have seldom been investigated. This study analysed the effects of a parasitic copepod on the larval growth of the Chilean triplefin Helcogrammoides chilensis (Tripterygiidae) based on the microstructure of the sagittal otoliths. Fish larvae were collected during the austral spring of 2010 off central Chile. Their body length ranged from 5.1 to 16.6 mm (2 to 57 days old). They were parasitised by a penellid larval copepod that was always externally attached to the ventral side of the fish's gut. The prevalence of the copepod ranged from 2.7% to 20.8%, with one to four parasites per fish larva. Relationships between otolith size (radius, perimeter) and larval size were equal for parasitised and unparasitised fish larvae (P > 0.05). Larval growth was also similar for unparasitised (0.21 mm/day) and parasitised fish larvae (0.19 mm/day) (P > 0.05). However, a comparison of same-aged larvae showed that the larvae with copepods were smaller in both length and estimated body volume than the larvae without copepods. The Recent Otolith Growth Index, indicated that larval H. chilensis with copepods showed a reduction in recent growth and condition compared with those without evidence of copepods (P < 0.05). Nevertheless, a higher parasite load (two vs. one pennellids) did not decrease the condition of the larval fish. The infestation of pennellids on coastal fish larvae may therefore induce an increase in the pelagic larval duration and potentially affect the settlement rates of this intertidal fish.