Length-Weight Relations and Monthly Occurrence of Juvenile Fish Species from the Donji Molunat Bay, Croatia (South-East Adriatic Sea) Dužinsko-maseni odnosi i mjesečno pojavljivanje juvenilnih riba

Length-weight relations (LWR) and monthly occurrence are presented for juvenile fi sh, sampled from April to December 2018. in the of Donji Molunat bay, Croatia. From total number of 1448 caught fi sh of 30 fi sh species, 699 individuals of 16 fi sh species: Atherina hepsetus, Chromis chromis, Coris julis, Diplodus annularis, Gobius bucchichii, Microlipophrys canevae, Oblada melanura, Oedalechilus labeo, Pagellus acarne, Sarpa salpa, Serranus scriba, Siganus luridus, Symphodus cinereus, Symphodus doderleini, Symphodus ocellatus and Symphodus rostratus were analysed. Two parameters were measured: total length (TL) using precision ruler to the nearest 0.1 cm, and weight (W) using digital balance to the nearest 0.1 g. The b values ranged from 2.731 to 3.427, with median 3.0305. This study provides the fi rst LWRs for juvenile fi sh species in the Donji Molunat bay, as that it can serve as a tool used for future reference.


INTRODUCTION / Uvod
Length-weight relation (LWR) has been used widely for fi sheries management and conservation. Since stock assessment models and management for fi sheries require information about body weight for estimation of biomass and regulation of catches, weight can be predicted from length using a weightlength relation (Froese et al. 2014.) It provides information on the condition factor and somatic growth type (isometric or allometric) of fi sh species and therefore it is used for the determination of the biomass, enabling the conversion of length to weight (Froese 2006, Froese et al. 2011). The exponent b from WLR can be used as a fundamental parameter to understand the structure of a fi sh population (Le Cren 1951, Froese 2006). LWR of a species depends on many factors: habitat, growth phase, season, size range, sex, health, fi sh condition, fi shing pressure… (Froese 2006, Karachle andStergiou 2008, Liousia et al. 2012).
The areas of shallow bays are important habitats in which a variety of species of fi sh and other marine organisms live. Particularly important areas for juvenile fi sh are areas covered with macrophytic algae and sea grass meadows (Blaber and Blaber, 1980.; Allen, 1982.; Guidetti, 1999.) That is a case in Donji Molunat bay, whose sea bed is covered by Posidonia oceanica, endemic sea grass of the Mediterranean Sea, while the bottom in shallow parts is pebbly (Dobroslavić et. al. 2010). Because of its high structural complexity, this bay is nursery and feeding place for a large number of fi sh species (Tutman, 2002). It is important to determine the number and monthly occurrence of juvenile fi sh species in this area, and their length-weight relations since they show fi sh growth patterns, which in turn are essential for developing of ecosystem based models for fi sheries.

MATERIAL AND METHODS / Materijali i metode
Fish samples were collected monthly from April to December 2018. In the Donji Molunat bay (N 42º 27´ 27, 5"; E 18º 25´ 34, 5") ( Figure 1). The fi sh samples were collected using small beach seine net, 25 meters long, 70 cm high at the beginning of the net wings, and 500 cm in the central part of the sac. The mesh size of net wings was 8 mm, and of the sac 4 mm. The average surface covered by this net at one pull is about 500 m 2 . After collection the fi sh samples were frozen and brought to the laboratory, where the measurements were made.
The length-weight relations were calculated on fi sh species with 5 and more individuals, and some fi sh species were excluded because of the errors in weighting. The fi sh were measured randomly for each species without sampling site and sex. Two parameters were measured: total length (TL) using precision ruler to the nearest 0.1 cm, and weight (W) using digital balance to the nearest 0.

RESULTS / Rezultati
During the sampling period, a total of 1467 juvenile individuals were caught from the Donji Molunat bay, representing the following families: Labridae (8 species), Sparidae (7 species Table 3 it is

DISCUSSION / Rasprava
Comparison of our data to the other work on the population of juvenile fi sh from Molunat Donji bay (Tutman, 2002), shows similar results. The most common fi sh species caught are Atherina hepsetus, Oedalechilus labeo, Sarpa salpa, Pagellus acarne and Coris julis. All of these species appear in present work with over 30 individuals, except one species, Oedalechilus labeo. In particular, for the three above-mentioned species (Gobius bucchichii, Oedalechilus labeo and Siganus luridus), the b values could be considered overestimated due to that the small number of sample (11, 12, and 7 individuals) and to that they cover a narrow range of length (Froese 2006 This study provides the fi rst LWRs from the Donji Molunat bay for all the reported species and it can serve as a tool used for future reference. Our fi ndings may well assist on monitoring and conservation of the natural nursery and feeding place for large number of juvenile fi sh species.