Biochemical response of two fish species of Gobiidae (Gobiiformes) to Cryptocotyle (Opisthorchiida, Heterophyidae) metacercariae infection from the mouth of the river Chernaya (Black Sea)

Metacercariae of Cryptocotyle are among the most numerously recorded trematode parasites in the estuarine biocenoses of the Azov-Black Sea basin. These parasites can massively affect body surface, gills and fins of host fishes including gobiids. However, information on the influence of Cryptocotyle metacercariae on the physiological and biochemical status of gobies is extremely limited. Biochemical response of two fish species of Gobiidae - grass goby Zosterisessor ophiocephalus (Pallas, 1814) and mushroom goby Ponticola eurycephalus (Kessler, 1874) to Cryptocotyle spp. metacercariae infection at the mouth of River Chernaya (Black Sea) was investigated. Activities of superoxide dismutase, catalase, peroxidase, glutathione reductase, glutathione-S-transferase, alanine transaminase, aspartate transaminase, level of thiobarbituric acid-reactive substances were measured as parameters of biochemical response. The findings of this study demonstrate interspecific differences in fish response to parasite infections. High infection leads to an intensification of lipid peroxidation and a weakening of antioxidant protection in the muscles of mushroom goby but activation of the antioxidant enzyme system in the muscles of grass goby. The results show a greater resistance of grass goby to the infection when compared with mushroom goby.

Tactic-specific differences in seminal fluid influence sperm performance

Seminal fluid often makes up a large part of an ejaculate, yet most empirical and theoretical studies on sperm competition have focused on how sperm characteristics (number and quality) affect fertilization success. However, seminal fluid influences own sperm performance and may potentially influence the outcome of sperm competition, by also affecting that of rivals. As a consequence males may be expected to allocate their investment in both sperm and seminal fluid in relation to the potential level of competition. Grass goby ( Zosterisessor ophiocephalus ) is an external fertilizer with guard-sneaker mating tactics, where sperm competition risk varies according to the tactic adopted. Here, we experimentally manipulated grass goby ejaculates by separately combining sperm and seminal fluid from territorial and sneaker males. While sperm of sneaker and territorial males did not differ in their performance when they interacted with their own seminal fluid only, sperm of sneakers increased their velocity and fertilization rate in the presence of territorial males' seminal fluid. By contrast, sneaker males' seminal fluid had a detrimental effect on the performance of territorial males' sperm. Sperm velocity was unaffected by the seminal fluid of males employing the same tactic, suggesting that seminal fluid's effect on rival-tactic sperm is not based on a self/non-self recognition mechanism. Our findings show that cross interactions of sperm and seminal fluid may influence the fertilization success of competing ejaculates with males investing in both sperm and seminal fluid in response to sperm competition risk.