Growth and otolith morphology vary with alternative reproductive tactics and contaminant exposure in the round goby Neogobius melanostomus

Abstract

Round goby Neogobius melanostomus sagittal (saccular) otolith morphology was compared between males of the two alternative reproductive tactics (termed guarder and sneaker males) and between males captured from sites of high or low contamination. Otolith size increased with fish size and also displayed an ontogenetic shift in shape, becoming relatively taller as otoliths grew in size. Despite a considerable overlap in age between males adopting the two reproductive tactics, size-at-age measurements revealed that guarder males are significantly larger than sneakers at any given age and that they invest more into somatic growth than sneaker males. Controlling for body size, sneaker males possessed heavier sagittal otoliths than guarder males. Subtle otolith shape differences were also found between the two male tactics and between sites of high and low contaminant exposure. Sneaker males had relatively shorter otoliths with more pronounced notching than guarder males. Fish captured at sites of high contamination had otoliths showing slower growth rates in relation to body size and their shapes had more pronounced caudal points and ventral protrusions when compared with fish captured at sites of low contamination. The results are discussed in relation to life-history tradeoffs between the male tactics in terms of reproductive and somatic investment as well as the putative metabolic costs of exposure to contaminants. Overall, this study reveals that male alternative reproductive tactics and environmental contaminants can have small, yet measurable, effects on otolith morphology and these factors should be accounted for in future research when possible.

Fish size effect on sagittal otolith outer shape variability in round gobyNeogobius melanostomus(Pallas 1814)

“…Bose et al . (2018) confirmed that N. melanostomus otolith size increased with fish size and also displayed ontogenetic shifts in shape becoming more elliptical with an increase in the otolith size. They also noted differences in the otolith weights of sneaker and guarder males (the latter had lighter otoliths) and also subtle otolith shape differences between the two male reproductive tactic groups and between fish caught at sites where they were exposed to high and low contamination.…”

Cryptic alternative male mating strategies in invasive alien round goby (Neogobius melanostomus) of the upper Danube River

“…This study provides evidence for the occurrence of alternative male mating strategies in round goby during their ongoing invasion of the upper Danube River (Table 2). Although this finding is novel in the context of a biological invasion process in the upper Danube River, alternative male mating strategies had been inferred for other round goby invasions, but with substantially different proportion estimates: whereas only about 4% round gobies were identified as sneakers in the invaded upper Danube River, much higher values of 40.6% in the River Rhine in the Netherlands (Bleeker et al 2017), and 39.3% (Bose et al 2018), 12 and 51% (Marentette et al 2009(Marentette et al , 2010 in the Great Lakes in the USA were found. A comparison of such proportions is challenging, however, because populations have different (invasion) histories, and exhibit different densities of conspecific and interspecific competitors (Cerwenka et al 2018), among other parameters.…”

“…Sneakers try to hide their male status by imitating females to fertilize foreign conspecific spawns (Taborsky et al 2008). Sneaker round gobies have a light mottled coloration, larger accessory sperm glands, a higher sperm volume, reduced 11-ketotestosterone levels (all: Marentette et al 2009), significantly larger testes, and heavier otoliths (both: Bose et al 2018). In the upper Danube River in Germany, round goby invasion processes, including spread, autecology, and impact on other species are well-studied (Brandner et al 2013a(Brandner et al , b, 2015Cerwenka et al 2014Cerwenka et al , 2017Cerwenka et al , 2018.…”

Population characteristics of the non-indigenous round goby, Neogobius melanostomus (Actinopterygii: Perciformes: Gobiidae), in the eastern Gulf of Finland

“…Age was estimated by examining otoliths cleared in glycerol (Kostûčenko 1961). Although sectioned and stained otoliths were recently recommended for age reading in the goby (Florin et al 2018), earlier studies were mainly conducted using whole otoliths (Kostûčenko 1961;Sokołowska and Fey 2011;Azour et al 2015;Bose et al 2018). Hence, we also applied whole sagittal otoliths to obtain comparable data with previous studies.…”