Ribarstvo, lovstvo i pčelarstvo

ORIGINAL SCIENTIFIC PAPER Age and growth determination of the grass goby (Zosterisessor ophiocephalus Pallas, 1814) in the Novigrad (Adriatic)

Željana Đođo¹, Jakov Dulčić², Nenad Antolović³ ¹University of Dubrovnik, Department of Aquaculture, Ćira Carića 4, Dubrovnik, Croatia ([email protected]) ²Institute of Oceanography and Fisheries, Šetalište Ivana Meštrovića 63, Split, Croatia ³University of Dubrovnik, Institute of Marine and Coastal Research, Kneza Damjana Jude 12, Dubrovnik, Croatia

Abstract The main objective of this study was to investigate the relationship between age and growth in the grass goby, Zosterisessor ophiocephalus (Pallas, 1814) in the Novigrad Sea. A total of 342 specimens, ranging from 4.5 to 20.2 cm were sampled. The age was determined by using otolith readings. Five age classes were established. Predominance of age class 2+ and 3+ in the total catch was noted. In comparison of sexes, differences were seen in the age classes. Males ranging in length from 6.7-20.2 cm were the most numerous in the 3+ age class, while females ranging in length 7.8-18.3 cm were the most numerous in the 2+ age class. Key words: Zosterissesor ophiocephalus, age, growth, Novigrad Sea

Introduction Goby () are one of the most numerous families (48 ) among Adriatic fish (Kovačić, 2004).They are mostly small fish that inhabit coastal marine seabed, in warm and moderately warm waters, but many of them thrive in brackish and fresh waters. There is a small number of pelagic species recorded (Miller, 1986). The grass goby is endemic to the (Fredj and Mourin, 1987), and Azov Sea (Fischer et al., 1987) while in the Adriatic they are very widespread, and most numerous in Novigrad and Karin Sea (Jardas, 1996). The grass goby, Zosterisessor ophiocephalus (Pallas, 1811), is a brackish goby. It is widely distributed in estuarine and lagoon environments. The meadows of sea grass and associated soft substrate provide an essential habitat for growth and reproduction (Gandolfi et al., 1991; Malavasi et al., 2002). The grass goby is an iteroparous species living up to 5 years, and is reported to reach sexual maturity at 2 or 3 years (Miller, 1984; Pinchuk et al., 2004). The present work aims to study the relationship between age and growth of the grass goby in the Novigrad Sea.

Material and methods Specimens of the Grass goby from the eastern part of the Novigrad Sea were taken from local fishermen with fyke nets, from January 2010 to February 2011. The seabed at the sampled location was muddy and sandy, with recorded depths of 3 - 4 meters (Fig. 1). There were 342 specimens measured for total length (TL ±0.1 cm). Age was determined by otolith readings, in respect to determined birth-month (Granzotto et al., 2003).

48. hrvatski i 8. međunarodni simpozij agronoma | Dubrovnik | Hrvatska 629 Fisheries, Game Management and Beekeeping

Figure 1. Map showing the study area, Novigrad Sea. Dashed line indicates the area where the net was set each month.

Results and discussion A total number of sampled Zosterisessor ophiocephalus was 342 individuals. Fish TL ranged from 4.5 to 20.2 cm. Number of 342 individuals, which were used for the age determination, consisted of 133 (38.8%) males, and 133 (38.8%) females, while for 76 (22.2%) sex was not determined. Length and age frequency distribution in total sample are shown in Graph 1.

Graph 1. Length-frequency distribution of the grass goby (Zosterisessor ophiocephalus) in total sample (N=342).

Adult males ranged in TL from 6.7 to 20.2 c, and females ranged from 7.8 to 18.3 cm. The dominance of males grass goby at 2+ age class, and females at 3+ age class could be

630 48th Croatian & 8th International Symposium on Agriculture | Dubrovnik | Croatia Ribarstvo, lovstvo i pčelarstvo related to selectivity of nets. An additional reason could be different distribution of younger and adult specimens inside the same coves. The higher mean TL value was found for 2+ year old females and 3+ year old males, which are significant differences between males and females in mean lengths at these ages. However, these inconsistencies could be an artifact from the sampling. The values obtained in this study correspond to results of Miller (1986), Fischer et al. (1987), and Akyol (2003). Females were the most numerous in the age classes: 2+ (33 %), and 3+, (23 %), which is presented in Graph 2. Males were the most numerous in the age classes 2+ (40%), and 3+ (39%) as it is presented in Graph 3.

Graph 2. Length-frequency distribution of the females of the grass goby (Zosterisessor ophiocephalus)

Graph 3. Length-frequency distribution of the males of the grass goby (Zosterisessor ophiocephalus).

48. hrvatski i 8. međunarodni simpozij agronoma | Dubrovnik | Hrvatska 631 Fisheries, Game Management and Beekeeping

Conclusion The results of the present study indicate differences in the abundance within the age classes between males and females. Males were abundant in age classes 3+, and female were abundant in age classes 2+.

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