ISSN: 0001-5113 ACTA ADRIAT., ORIGINAL SCIENTIFIC PAPER AADRAY 62 (1): 49 - 62, 2021 Reproductive strategy of spiny gurnard Lepidotrigla dieuzeidei Blanc and Hureau, 1973 from the south-eastern Adriatic Sea Tatjana DOBROSLAVIĆ1*, Alexis CONIDES2, Jadranka SULIĆ ŠPREM3, Branko GLAMUZINA1 and Vlasta BARTULOVIĆ1 1University of Dubrovnik, Department of Applied Ecology, Ćira Carića 4, Dubrovnik, Croatia 2Hellenic Centre for Marine Research, 46.7 km Athens-Sounion, Anavyssos, Greece 3Dubrovnik Natural History Museum, Dubrovnik, Croatia *Corresponding author: [email protected] This study provides the first data on the reproductive biology of the spiny gurnard Lepidotrigla dieuzeidei. A total of 1027 individuals were collected monthly from September 2011 to August 2012. The total length of the individuals in the sample ranged from 7.46 cm to 14.62 cm with a female to male ratio of 1 to 0.59. Positive allometric growth was observed for both females (b=3.07) and males (b=3.08). Variations of condition factor were similar in both sexes with mean values of 1.07 for females and 1.01 for males. The fish L. dieuzeidei had a long spawning period extending from November to July based on monthly values of gonadosomatic index. Histological analysis showed that this fish was multiple synchronous developments of ovaries with multiple spawning events. The ovaries were always represented with a group of primary oocytes and a diverse population of vitel- logenic oocytes, each specially recruited during the final stages of maturation in uniform or uneven phases. Batch fecundity was estimated gravimetrically using the hydrated oocyte method and was estimated to be around 558 to 10.230 oocytes per female. L. dieuzeidei is an important by-catch species and data from this study represent a valuable contribution to stock management Key words: oogenesis; spermatogenesis; gonad maturation; fecundity; oocyte diameter; multiple spawning fishes INTRODUCTION directed at a restricted number of target species. The main target fish species for the demersal Fisheries of deeper Adriatic Sea waters are trawl fishery are European hake (Merluccius mainly executed at depths of 200-300 m and merluccius), red mullet (Mullus barbatus bar- it represents the largest area of occurrence of batus), breams (Pagellus spp.), whiting (Mer- demersal shared stocks in the Mediterranean. langius merlangus), anglerfish (Lophius spp.), Many different fishing gears exploit the demer- flatfish (Solea solea, Scophthalmus maximus, sal communities but trawl net represents the Scophthalmus rhombus, Platichthys flesus). main gear in terms of catch and fleet power Studies of the impact of fishing have mostly (CADDY, 1993; SÁNCHEZ et al., 2007). However, focused on the target and economically impor- trawling exploitation in the Adriatic Sea is tant species and little is known about the impact 50 ACTA ADRIATICA, 62 (1): 49 - 62, 2021 Considering the lack of crucial biological data for this species, the main objective of this study was to investigate the annual reproductive cycle of L. dieuzeidei in the Adriatic Sea. Sex ratio, length at sexually maturity, gonadoso- matic index, fecundity, gonad development and oocyte size were analysed to obtain insight into the spawning activity for this by-catch species. Knowledge of reproductive biology of a fish species is essential for stock assessment and effective fishery management. MATERIAL AND METHODS Fig. 1. Location of commercial fishing from town Dubrovnik to the north point of Pelješac peninsula (line), southern Adriatic Sea Sampling site, procedure and measurements to non-target species that have none or small Samples were collected from south Croatian economic value and have been characterized as offshore waters between the city of Dubrovnik by-catch species. One of the frequent by-catch and the north point of Pelješac peninsula (Fig. species is spiny gurnard Lepidotrigla dieuzeidei 1). A total of 1027 individuals were collected Blanc & Hureau, 1973 from the family Trigli- monthly, from September 2011 to August 2012. dae. It is a small benthic species distributed in Specimens were caught at depths between 170 the eastern Atlantic and the western and mid- and 230 m using bottom trawl net (2 hauls, dle Mediterranean Sea and it prefers sandy and each lasted for approximately 5 h) during com- muddy bottoms at a depth between 60 and 180 m mercial fishing activities (vessel engine power (JARDAS, 1996). There are around 114 species of 60kw). The total length of the net was 45 m family Triglidae in the world and only 8 species with a mesh size of 60 mm and cod-end 24 divided into 5 genera exist in the Mediterranean mm, measured knot to knot. After catching all and the Adriatic Sea. L. dieuzeidei and large- specimens were put on ice and transported to scaled gurnard, L. cavillone are the only rep- the laboratory for further analysis. For each fish, resentatives of the genus Lepidotrigla. Despite total length (Lt) was measured using a simple the high abundance of gurnard species, little is calliper to the nearest 0.1 mm and weighed (W) known about the biology of L. dieuzeidei, espe- to the nearest 0.1 g. Fishes were gutted, and cially reproduction data. For the Adriatic Sea, gonads were removed and weighed (Wg) with only available data for this species is an elliptic three decimal accuracy. Sex was determined by analysis of otoliths (MONTANINI et al., 2010). macroscopic observation of the gonads (MACER, Previous studies in other parts of the Medi- 1974). To test differences in relation to the terranean are based on the first record with the expected ratio 1:1, the sex ratio was examined morphometric and meristic description of this using Chi-square (χ2) test with a probability species (ERYILMAZ, 2002; BAÑÓN, 2004; DALYAN level of 0.05. Age was estimated by interpreting & ERYILMAZ, 2006). The weight-length relation- growth rings on otoliths from 200 individuals. ship was investigated in the Mediterranean After removal otoliths were cleaned in distilled (TORRES et al., 2012; BAŞUSTA et al., 2013a) and in water, immersed in glycerol and examined with the south coast of Portugal (OLIM & BORGES, stereomicroscope on a black background under 2006) while the age and growth and relationship reflected light. Some otoliths were polished with between total length and otoliths dimensions sandpaper (type P220 and P80) due to calcium were analysed in the northeast Mediterranean accumulation. Age estimations were made by (BAŞUSTA et al., 2013b; BAŞUSTA et al., 2017). three readers if the readings did not coincide Dobroslavić et al: Reproductive strategy of spiny gurnard Lepidotrigla dieuzeidei Blanc and Hureau, 1973 ... 51 the otolith was rejected. Transparent and opaque lace and Selman (1981) and testes TAKASHIMA rings were counted, one transparent and one & HIBIYA (1995). For quantitative analysis oocyte opaque ring was considered as one year. diameter was measured using an image analy- sis system (AxioVision Release 4.8. software). Data analysis Male germ cells were classified as spermato- gonia (Sg), spermatocytes (St), spermatids (Sd) Growth was analysed using von Bertalanffy and spermatozoa (Sz) (GRIER, 1981). growth equation: Lt = , where is the asymptotic It should be noted that the selection of the length, k is the growth coefficient, and is the ovaries used for fecundity estimation was based hypothetical age for Lt=0 (TOMLINSON & NOR- on gonad histological sections showing that MAN, 1961). To describe the length-weight rela- postovulatory follicles were not present. Batch tionship, allometric growth equation was used: fecundity was estimated gravimetrically using W = a*Lb (RICKER, 1977), where W is the total the hydrated oocyte method, where only oocytes weight (g), L is the total length (mm) and a and larger than 500 µm were counted (HUNTER et al., b are constants estimated by last square method. 1985). For each selected ovarian sample, three Fultonʼs condition factor was calculated follow- subsamples of 0.01 g from the anterior, central ing Froese (2006): K=, where W is total body and posterior region of the gonad lobe were weight (g) and L is the total length (mm). taken for counting migratory nuclei and hydrat- The spawning period was established based ed oocytes. Batch fecundity for each female was on the monthly variation of the gonadosomatic estimated as the mean value of three subsamples index (GSI) and calculated as GSI = 100*Wg that have been calculated as the number of the / W, where Wg is gonad weight (g) and W is migratory nuclei and hydrated oocytes per unit the total weight (g) (RICKER, 1977). To estimate weight of the subsample and the total weight size at first sexual maturity, the data were fitted of the gonad. Regression analyses were car- in the equation: P = 1/(1+e(a-b*L)); where P ried out relating fecundity to total length (Lt), is the probability that individuals are sexually total weight (W) and gonad weight (Wg). The matured, L is their length and a, b coefficients. relationships fecundity-length, fecundity-weight The length when 50% of analysed individu- and fecundity-gonad weight were express by als were mature was calculated according to equation F = a, where F is the fecundity, X either SPARRE & VENEMA (1998) as L50%=a/b. Lt, W or Wg, a is the constant and b is the expo- For histological analysis 30 individuals, ran- nent (BAGENAL, 1978). domly selected, from both sexes were used monthly. After weighing, gonads were fixed in Statistical analysis 8% buffered formalin. A small piece of tissue from the middle of the gonad was tested. After Comparison between means was performed dehydration and clearing, tissue was embedded using ANOVA test with multiple comparison in paraffin, sectioned on a microtome (5 µm) tests (Tykey and Duncan) to identify similar- and stained with hematoxylin and eosin dye. All ity groups. Relations between time-series was histological sections of ovaries were classified analysed using the Cross Correlation Function to assess the oocyte developing phase accord- (CCF) while the statistical difference between ing to TYLER & SUMPTER (1996) and BROWN- time series was analysed using the chi-square PETERSON et al.