How old are you-Evaluation of age reading methods for the invasive round goby (Neogobius melanostomus , Pallas 1814)

Abstract

Summary In the Baltic, the first observation of the round goby (Neogobius melanostomus, Pallas 1814) was made in 1990. Within the past decade the species became invasive and spread rapidly throughout the Baltic Sea. Studies about the fishes potential impacts on resident species promote the need for an increasing knowledge of their basic stock structures such as growth rates, longevity and mortality, which all rely on accurate estimates of age. Former studies on the round goby have used several different age reading techniques. In this study, we compared three standard otolith preparation methods for ageing and present the best procedure for the invasive round goby. The results showed significant differences in age estimates of the same fish between the different preparation methods and between readers. The estimation of the first annulus, the first year, was the most problematic. The overall agreement was lowest when reading the whole otoliths while the best performance was achieved with sectioned and stained preparation method. Depending on method used the growth estimates also differed. The results question comparability between previous studies and highlight the importance of harmonised aging procedures for the round goby for obtaining correct estimates of population parameters such as growth rate, age at maturity, and longevity.

Habitat utilization and feeding ecology of small round goby in a shallow brackish lagoon

“…The presence of small, mainly juvenile, round gobies at the study site might be related to its relatively young invasion history as small round gobies have been linked to more recently colonized sites and larger individuals to originally invaded areas (Ray and Corkum 2001). Round gobies at our study site reached a total length of up to 14 cm and therefore seemed to be aged between 0 and 5 years according to Florin et al (2018), which would be in accordance with their presumptive young invasion history in Greifswald Bay (study performed 3 years after first observation).…”

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.…”

Age determination in the icefish Pseudochaenichthys georgianus (Channichthyidae) based on multiple methods using otoliths

“…Unfortunately, almost all earlier collected otoliths of Pseudochaenichthys georgianus were either crushed, broken, burnt (Chojnacki & Palczewski 1981) or unsuccessfully assessed by traditional LM methods of estimating age (Mucha 1980) with unacceptably large errors (Takács et al 2016). A few otoliths were prepared by Florin et al (2018) for daily microincrement counts via LM and SEM. Their LM images showed daily micro-increments, whose smallest widths were determined by Kellermann et al (2002) as 0.00038− 0.00075 mm and even less than 0.0002 mm by Radtke (1990).…”

“…However, under SEM high magnification, the daily pattern nearly disappears; therefore, the SEM may not give as clear a result as the LM. Nonetheless, with the SEM technique, an investigator automatically counting daily micro-increments with the micro-densitometer does not need several repetitions to determine otolith microstructures (Takács et al 2016, Florin et al 2018, whereas Kellermann at al. (2002) required 3 time-consuming blind counts.…”

“…However, their bones are largely replaced by cartilage and their skeletons undergo constant metamorphosis (Żabrowski 2000), which excludes skeletal bone from icefish aging. Therefore, otoliths have become the aging structure of choice (Kock 1989, Florin et al 2018. Of the 3 otoliths in the head, the sagittae show the greatest increase in size as the fish grows and are therefore preferred for aging (Kock 1989).…”