Studio sui calamari Loligo vulgaris (Lamarck, 1798) e Loligo forbesii (Steenstrup, 1856) delle acque della Sardegna

This thesis aims to deepening knowledge on the biology and ecology of the two squids Loligo vulgaris (Lamarck, 1798) and Loligo forbesii (Steenstrup, 1856) from Sardinian waters. Considering their socio- economic importance in the Sardinian fisheries, the annual fluctuations in abundance highlighted the possibility of set management measures for their rational exploitation on the base of the knowledge of their life cycle Even if their different preferential bathymetric range, the study of the reproductive process through macroscopic histological and gravimetric analysis of the reproductive systems showed similarities between the two squids both in morphology of the gonads and in the pattern of reproduction. They are similar because they show an extended period of sexual maturity; they have an intermittent spawning with intermediate characteristics between coastal and deep spawning. In particular specific results on the reproductive output of L.vulgaris, showed a potential fecundity of about 4000 eggs (size 0.30-3 mm) and 436 spermatophores (size 7.25-17.37 mm) according to the few studies so far carried out on the species. The reading of the age from the eye lens, tested here for the first time on cephalopods decapods, has allowed to estimate for both species a life cycle of about 18-20 months. For both squids were also performed morphometric analysis of the beaks and calculated specific correlations with the animal size. Considering the taxonomic value of the beak such information may be helpful in studies on diets of predators of these species

Age estimation in Sepia officinalis using beaks and statoliths

Establishing the age of cephalopods is crucial for understanding their life history, which can then be used for assessment and management. This is particularly true for the common cuttlefish Sepia officinalis (Linnaeus, 1758), one of the most important resources for coastal fisheries. For this reason, an age analysis of S. officinalis was performed for the first time in the Mediterranean, using beaks and statoliths from 158 wild specimens (55–222 mm mantle length; 23–1382 g total weight) at different maturity stages (immature to mature). Growth increments were counted in the lateral wall of the upper beaks and the lateral dome of statoliths. In both cases, a good relationship was found between the counts and the sizes of the animals. The low values of coefficients of variation between the readings obtained for beaks (3.96 ± 1.87%) and statoliths (4.00 ± 1.89%) showed a high level of precision and accuracy in the readings. However, the analysis was simpler for beaks, which were all successfully analyzed, while it was more complex for statoliths, with 69% being lost due to rejection or overgrinding. Based on daily increments previously validated in statoliths, the beaks were cross-verified by comparing their counts with those from statoliths extracted from the same 83 specimens, obtaining a statistically significant relationship between the two counts, confirmed by the ANOVA test. Absolute growth rates that were assessed using both beaks and statoliths indicated that the two sexes had a higher growth rate at 122 and 182 days, which subsequently declined in older specimens. Due to the relative simplicity of its processing method, the beak was finally proposed as a suitable hard structure to study the age of S. officinalis. We also confirmed the good readability of increments in the lateral wall of the beak, which could be considered a valid alternative to the rostrum surface

On a female of Tremoctopus sp. (Octopoda: Tremoctopodidae) caught in the Sardinian Sea

Morphometric and biologic data on a maturing female of Tremoctopus sp. (Octopoda: Tremoctopodidae) from the Sardinian Sea are provided. Potential fecundity and oocytes size values, reported for the first time in the western Mediterranean Sea, have suggested a possible different reproductive investment between the two basins of the Mediterranea

On a female of Tremoctopus sp. (Octopoda: Tremoctopodidae) caught in the Sardinian Sea = Su una femmina di Tremoctopus sp. (Octopoda: Tremoctopodidae) catturata nel mare di Sardegna

Morphometric and biologic data on a maturing female of Tremoctopus sp. (Octopoda: Tremoctopodidae) from the Sardinian Sea are provided. Potential fecundity and oocytes size values, reported for the first time in the western Mediterranean Sea, have suggested a possible different reproductive investment between the two basins of the Mediterranean

Finding of two Loliginidae egg masses in the Sardinian waters

Data of two egg masses of Loliginidae collected in Sardinian waters are reported. The depths of finding, the differences in appearance of the capsules and in the egg size between the two masses, have suggested that they belong to the two species, Loligo forbesii and Loligo vulgaris

Artificial dens for Octopus vulgaris Cuvier, 1797 in the Sardinian Sea

Monitoring on 244 artificial dens from 2011-2013 in the Sardinian Sea, showed that Octopus vulgaris (Cephalopoda: Octopoda) chose them as shelters (40.72%), staying inside (86.67%) or leaving only signs of its occupation (13.33%). The 58.97% of the dens with animals inside had spawning females, with their eggs completed the embryological development. These preliminary results suggest the use of artificial dens in fishing management to protect the octopus stock

Male reproductive system and sexual products in Histioteuthis bonnellii (Cephalopoda: Histioteuthidae)

The reproductive systems of 119 males of the umbrella squid Histioteuthis bonnellii (Férussac, 1835) caught in the Sardinian waters (Central Western Mediterranean) at depths between 400 and 700 m were examined and are described for the first time. Fully mature males were present all year round. The smallest mature male measured 60.0 mm in mantle length (ML) and 113.50 g in body weight, and the sizes at maturity were 100.0 mm ML and 400.00 g TW. The total number of spermatophores was counted in 18 specimens, and varied from 12 to 3097 (977±928), without correlation with body size. Spermatophore total length (SpL) ranged between 3.00 and 15.45 mm (7.11±3.49). SpL gradually decreased towards the distal end of the reproductive system, so that spermatophores found in the proximal part of the Needham’s Sac were larger than those found in the terminal organ, and this difference in length was conspicuous (i.e., up to over 200%). Only the SpL of spermatophores from the proximal part of the Needham’s Sac was correlated with body size. Both indices of the sperm mass and of the ejaculatory apparatus decreased with the increase of spermatophore length, while the cement body index increased. Spermatangia were found in 13 specimens, exclusively in the terminal organ. Up to 64 spermatangia (21±17), measuring between 2.02 and 8.12 mm in length (4.44±1.88 mm), were counted. The large size range of mature males (ML 60.0–198.0 mm; TW 113.50–2409.00 g) and the variation in spermatophore number indicate that in H. bonnellii males the production of sexual products is a process that starts early in the individual life and extends in time, while animals continue to grow and mate, releasing spermatophores at different times. A continuous production of sexual gametes is already known and better investigated in females of deep-sea cephalopods, where it is considered a reproductive adaptation to depth (Rocha et al., 2001). A similar strategy, that increases the time interval in which reproduction can take place, was proposed recently for H. miranda males from the South African waters by Hoving et al. (2010). Indeed, as evidenced by these authors, an early and continuous production of spermatophores allows a maximum time range for mating; this, in deep-sea environments where low density of individuals and scarcity of spawning aggregations may occur, would result in a winner reproductive strateg

Chromosome Mapping of 5S Ribosomal Genes in Indo-Pacific and Atlantic Muraenidae: Comparative Analysis by Dual Colour Fluorescence In Situ Hybridisation

The Muraenidae is one of the largest and most complex anguilliform families. Despite their abundance and important ecological roles, morays are little studied, especially cytogenetically, and both their phylogenetic relationships and the taxonomy of their genera are controversial. With the aim of extending the karyology of this fish group, the chromosomal mapping of the 5S ribosomal gene family was performed on seven species belonging to the genera Muraena and Gymnothorax from both the Atlantic and Pacific oceans. Fluorescence in situ hybridisation (FISH) experiments were realized using species-specific 5S rDNA probes; in addition, two-colour FISH was performed to investigate the possible association with the 45S ribosomal gene family. Multiple 5S rDNA clusters, located either in species-specific or in possibly homoeologous chromosomes, were found. Either a syntenic or different chromosomal location of the two ribosomal genes was detected. Our results revealed variability in the number and location of 5S rDNA clusters and confirmed a substantial conservation of the number and location of the 45S rDNA

Movement estimation of Octopus vulgaris Cuvier, 1797 from mark recapture experiment

The movements of Octopus vulgaris were investigated by a mark-recapture study (1604 specimens tagged), carried out during a commercial octopus traps fishery, at a depth of 20-50. m, over a rocky substrate area of the Sardinian Sea (central western Mediterranean Sea). Overall 87 specimens (56 males and 31 females) were recaptured after 4 and 63. days from the tagging. The difference between the depth at release and recapture varied up to 5.0. m but in 100% of males and in 80% of females the variation was less than 3.0. m. Theoretical straight distances travelled by recaptures ranged from 9 to 5800. m in males and from 9 to 1700. m in females, regardless of the days of freedom.There was no correlation between distances and sex or body size and no marked orientation was found except for medium males that move preferentially in the south western direction. The movements of O. vulgaris, generally linked to the availability of food, partners and/or shelters, in this study were limited within 1. km in most of the recaptures (84-86%). This high site fidelity, within the rocky area investigated, could represent useful information for management plans of this species like the creation of small no-take areas. vulgaris are discusse

Age estimation and back-calculation of fish length of the European hake, Merluccius merluccius (Linnaeus, 1758) in Sardinian waters

Aim of the present study is to evaluate the growth parameters for the European hake, Merluccius merluccius, in Sardinian waters by means of otolith annual ring analysis, providing also an indirect validation through the use of back-calculation. A total of 283 individuals (of which 150 males, ranging from 8.5 to 42.1 cm TL, and 133 females, that ranged from 11.2 to 83.3 cm TL), collected during the MEDITS survey in 2012 and 2013, were selected for the age reading. The determination of the age was carried out on the whole otolith for fish with total length smaller than 20 cm while for the others a transversal section across the core was prepared. Hyaline rings count was performed twice by two different readers, showing good reproducibility (%CV= 13.9; IAPE= 10.69). The estimated von Bertalanffy parameters (± s.e.) were Linf= 53.26 ± 10.15, k= 0.17 ± 0.06, t0= -1.73 ± 0.26 and Linf= 102.77 ± 13.67, k= 0.09 ± 0.02, t0= -1.46 ± 0.13 respectively for males and females. Back-calculation, carried out on otolith sections through the measurement of the ventral radius of each annulus, has provided an estimation of fish size at each year. Mean length at each age class (1-6 for females, 1-4 for males) obtained with the two methods was compared individually showing no statistically significant differences (t-Student, p-value> 0.05), except for age class 1 for both sexes. This result is probably due to the difficulty, well-known in literature for the European hake, in the identification of the first year annulus, which could be confused with one of the false rings around the nucleus. Nevertheless, this procedure certainly offers a valuable mean for corroboration of the age determination when other validation analysis are not achievable