Frane Škeljo

The effect of artificial feed on blood biochemistry profile and liver histology of wild saddled bream, Oblada melanura (Sparidae)

Floating fish farms attract a great number of wild fish species, changing their behaviour and physiology. The saddled bream, Oblada melanura, sampled from populations aggregated around the Adriatic fish farm and from natural/control populations, were analysed for differences in eleven blood biochemistry parameters and liver histomorphology. The levels of lactate dehydrogenase (LDH), alkaline phosphatase (ALKP) and urea (URE) in cage-associated saddled bream (428.00±SD 321.56 U/L, 86.13±SD 39.87 U/L and 0.05±SD 0.16 mmol/L, respectively) were significantly lower than those observed in the control specimens (1047.06±SD 505.56 U/L, 125.75±SD 34.70 U/L and 1.99±SD 0.73 mmol/L, respectively). In contrast to that, concentrations of aspartate aminotransferase (AST) in cage-associated fish (87.63±SD 132.34 U/L) were higher than values noted for the control population (6.55±SD 5.90 U/L). URE and AST presented the main variables contributing to the discrimination between two analysed populations. One-way ANOSIM based on the blood parameters showed significant difference between saddled bream that fed around cages and those from the remote waters (R=0.697; P < 0.01). Hepatocytes of cage-associated fish contained large cytoplasmatic clear spaces indicating excessive accumulation of fat in the hepatocyte cytoplasm. All observed differences can be attributed to contrasting feeding behaviour of sampled populations but basic nutritional differences between them should be quantified in the future. Moreover, further research is necessary to detect their impact on the health status of the fish.

Old Info for a New Fisheries Policy: Discard Ratios and Lengths at Discarding in EU Mediterranean Bottom Trawl Fisheries

Discarding is considered globally among the most important issues for fisheries management. The recent reform of the Common Fisheries Policy establishes a landing obligation for the species which are subject to catch limits and, in the Mediterranean, for species which are subject to Minimum Conservation Reference Size (MCRS) as defined in Annex III to Regulation (EC) No 1967/2006. Additionally, several other initiatives aim to reduce unwanted catches of target and bycatch species, including species of conservation concern. This raises the need to study discarding patterns of (mainly) these species. In this work we collated a considerable amount of historical published information on discard ratios and lengths at discarding for species caught in EU Mediterranean bottom trawl fisheries. The main aim was to summarize the available historical records and make them more accessible for scientific and managerial needs, as well as to try identifying patterns in discarding. We show discard ratios and lengths at which 50% of the individuals were discarded (L50) for 15 species (nine bony fishes, three crustacean decapods and three elasmobranchs). Discard ratios were usually low for target species such as hake, red mullets and highly commercial shrimps and exemptions from the landing obligation under the de minimis rules could be sought in several cases. Discard ratios were usually higher for commercial bycatch species. Discarding is affected by a combination of factors and for a given species, especially for non-target ones, discards are likely to fluctuate within a fishery, across seasons, years and regions. For most species considered, L50s were lower than the MCRS (when in place) and length at first maturity. L50s of target species, such as hake, were very small due to the existence of market demands for small sized individuals. However, for species of low demand, like horse mackerels, a higher retention size was observed, often exceeding MCRS. Lengths at discarding are affected by legal provisions, market demands but also by biological, population and ecological traits. Understanding the factors that affect discarding constitutes the starting point for designing mitigation measures and management plans to reduce discards and improve the sustainability of the stocks.

A preliminary study on the age and growth of the argentine, Argentina sphyraena (Actinopterygii: Osmeriformes: Argentinidae) from the eastern Adriatic Sea

Background. Age determination is a basic step in understanding fish biology and dynamics of fish populations. The only available data on the age and growth of argentine, Argentina sphyraena Linnaeus, 1758, a noncommercially exploited species of the family Argentinidae, was published almost half a century ago. More recent reports are limited to general biological characteristics of A. sphyraena so the main goal of our study was to fill a gap by investigating age and growth of the eastern Adriatic population of this fish. Materials and methods. Samples of the argentine were collected in the eastern Adriatic Sea, during March 2011, using a bottom trawl. We analysed sagittal otolith morphology and morphometry; the age of each fish was determined from the number of growth zones on otoliths and relations between the observed otolith age and otolith morphometrics were constructed using a power model. Mean length-at-age was described using the von Bertalanffy growth model. Results. Sagittal otoliths of Argentina sphyraena displayed alternating opaque and translucent zones. The maximum observed age was 3 years for both females and males. Females that were 2+ and 3+ years old were the most numerous in the sampled population. The estimated values of the von Bertalanffy growth model parameters were: L∞ = 17.57 cm; k = 0.40 year –1; t0 = –1.39 years. The age of the argentine can be best predicted from the otolith thickness. Conclusion. The maximum lengths and ages recorded in this study confirmed that in warmer southern latitudes, Argentina sphyraena attains a smaller maximum size. It should be emphasized that the presented model described the growth of fish ages 1–3 and therefore is probably representative only for younger age groups of argentine.

Age and growth of the axillary wrasse, Symphodus mediterraneus (L.) from the eastern Adriatic Sea

Abstract The age and growth of Symphodus mediterraneus were determined by examining the sagittal otoliths of 245 specimens (81 males, 160 females and four individuals of indeterminate sex) collected in the eastern Adriatic Sea between October and December 2009. Total lengths of males and females ranged from 74 to 154 mm and from 51 to 131 mm, respectively. Polished otoliths displayed well-defined alternating opaque and translucent rings. Age was determined by two independent readers who considered one opaque and one translucent ring to represent one year’s growth. In order to determine the first annual ring we examined daily rings and concluded that the first opaque annulus roughly corresponds with the first year of life. Most of the specimens were between two and three years old, with the maximum observed age of three years for males and five years for females. The length-at-age was described by the von Bertalanffy growth curve and significant differences were found between males (L∞ = 16.09 cm, k = 0.50 and t0 = –0.83) and females (L∞ = 14.11 cm, k = 0.33 and t0 = –1.42).