Reproductive characteristics of Spondyliosoma cantharus (Linnaeus, 1758) in the Gulf of Tunis

The reproductive features of Spondyliosoma cantharus were studied in the Gulf of Tunis to contribute to better fisheries management on a regional scale and to broaden knowledge on whether there are actual performance differences compared to others areas. A total of 369 fish were caught by trammel and gill nets in the Gulf of Tunis from January 2005 to June 2006. Sex‐ratio, gonad maturation, size and age at maturity, sexual cycle, condition and reproductive strategy were determined. The male : female ratio was initially skewed in favour of females, with males predominating in larger sizes. Length of females at first maturity was 17.8 cm TL (n = 141), which corresponds to 4 years of age. A recommendation is made to increase the length at capture. Spawning season extends from January to May, with a peak in March–April correlated to the lowest sea surface temperatures (14.8–15.6°C); during this period, a dichromatism arises between males and females. The hepatosomatic index and the condition factor present significant monthly changes in relation to the breeding activity. The bimodal size frequency distribution, the biased sex ratio, and the presence of bisexual gonads outline a protogynous hermaphroditism; diandry should be confirmed.     

Fine structure of spermatozoa in the gilthead sea bream (Sparus aurata Linnaeus, 1758) (Perciformes, Sparidae)

Scanning and transmission electron microscopy were used to investigate the fine structure of the sperm of the sparid fish Sparus aurata L. The mature spermatozoon of gilthead sea bream belongs, like that of the other sparid fish, to a "type I" as defined by Mattei (1970). It has a spherical head which lacks an acrosome, a short, irregularly-shaped midpiece and a long cylindrical tail. The nucleus reveals a deep invagination (nuclear fossa) in which the centriolar complex is located. The two centrioles are approximately perpendicular to each other and show a conventional "9+0" pattern. The proximal centriole is associated with a cross-striated cylindrical body lying inside a peculiar satellite nuclear notch which appears as a narrow invagination of the nuclear fossa. The distal centriole is attached to the nuclear envelope by means of a lateral plate and radial fibres made of an electron-dense material. The short midpiece houses one mitochondrion. The flagellum is inserted perpendicularly into the base of the nucleus and contains the conventional 9+2 axoneme.     

Characterization of eight microsatellite markers in the white sea bream, Diplodus sargus (Teleostei, Sparidae)

The white sea bream, Diplodus sargus (Teleostei, Sparidae), is a species with a high commercial importance in Mediterranean aquaculture. There is currently little information available about the genetic characteristics of cultured populations. In this survey, we have developed eight polymorphic microsatellites for the white sea bream using an enriched genome library protocol. All of them were polymorphic in the 67 individuals tested, 32 of which were wild specimens, and 35 were individuals from a captive F(1) broodstock. These markers can potentially be useful tools for use in population genetic studies.     

Age,growth and reproduction of the sand smelt Atherina boyeri Risso, 1810 in Mellah Lagoon (Eastern Algeria)

This aim of this paper was the study of the reproductive biology and growth of the sand smelt, Atherina boyeri, in Mellah Lagoon (Algeria). These data are important for the sustainable exploitation of the stocks of this species. Examined was a total of 1402 Atherina boyeri specimens captured monthly from March 2010 to March 2011, in a population with a 3‐year life cycle. Length–weight relationship was estimated as W = 0.0047 L^3.077 (r² = 0.935) for males and W = 0.0047 L^3.176 (r² = 0.935) for females. Using scales, the von Bertalanffy growth function fitted to back‐calculated size‐at‐age data was Lt = 9.49 [1 ? e^{?0.316 (t + 0.928)}] for males, and Lt = 11.67 [1 ? e^{?0.179 (t + 1.514)}] for females; using otoliths this was Lt = 9.68 [1 ? e^{?0.3 (t + 1.02)}] for males, and Lt = 11.93 [1 ? e^{?0.171 (t + 1.55)}] for females. The growth performance index (Φ) indicated that males (Φ_scales = 3.34, Φ_otoliths = 3.33) grew at the same rate as females (Φ_scales = 3.19, Φ_otoliths = 3.24), with a sex ratio of 1 : 1.6 in favor of females. The reproductive season extended from February to June. Individual length at first sexual maturity was 4.20 cm for 1‐year‐old males and 4.35 cm for 1‐year‐old females.     

Novel polymorphic microsatellite loci for the protogynous hermaphrodite slinger sea bream (Chrysoblephus puniceus, Sparidae)

As a result of the global decline of fish stocks, an increasing number of fish species are becoming targets of heavy exploitation, often concomitantly with a lack of biological knowledge on their structure and demographics. Here we present 11 new polymorphic microsatellite loci, isolated from the slinger sea bream (Chrysoblephus puniceus, Sparidae), a relatively recent target of coastal fisheries in eastern South Africa. Levels of genetic diversity were assessed in 39 individuals collected from the KwaZulu-Natal coast (Park Rynie, South Africa). Observed and expected heterozygosities varied between 0.39 and 0.97 and between 0.53 and 0.96, respectively. One locus (SL35) showed significant heterozygote deficiency and linkage disequilibrium was detected between SL35 and SL1. Importantly, five of these microsatellites cross-amplify in Cheimerius nufar, a sympatric species also subjected to exploitation.     

Age, growth, reproduction and mortality of the striped seabream, Lithognathus mormyrus (Pisces, Sparidae), off the Canary Islands (Central-east Atlantic)

Striped seabream, Lithognathus mormyrus L. (n=731) caught off the Canary Islands from January 1999 to June 2000 were studied. Fish ranged in size from 113 to 372 mm total length, weighing from 21.1 to 748.2 g total weight. Weight increased allometrically with size (b=2.9071). Fish age was 0–10-years-old. Growth was relatively slow (k=0.88 years⁻¹), with females growing at a slightly faster rate than males. The species displayed protandric hermaphroditism. Male : female ratio was unbalanced in favour of males (1 : 0.85). Males predominated in smaller sizes, females in larger sizes, and intersexual individuals were in intermediate sizes. The reproductive season extended from June to December, with a peak in spawning activity in August–September. Males reached maturity at 207 mm (2 years) and females at 246 mm (3 years). The real value of instantaneous rate of natural mortality was between 0.30 and 0.45 years⁻¹.     

黑鲷的胃排空率

在实验室内,１８℃条件下测量了体重在２０－４０ｇ的黑鲷的胃排空率,并用３种数学模型拟合了黑鲷的排空率,结果表明,３种模型都能很好地拟合实验数据,但通过统计学分析发现不论是用湿重还是用于重表示胃含物,线性模型都拟合得最好。用湿重表示时模型为Ｙ＝１．１４－０．０６ｔ（ｒ＾２＝０．８２,ｐ〈０．００１）;而用干重表示时模型为Ｙ＝１．３６－０．０７Ｔ（ｒ＾２＝０．６２,ｐ〈０．００１）,实验还得出体重２０     

Age,growth and reproduction of the white seabream Diplodus sargus sargus (Linneaus, 1758) off the eastern coast of Algeria

The objective of this study was to determine the basic population‐specific parameters necessary for fish stock assessment in the area and to compare these with data from other Mediterranean regions. White seabream Diplodus sargus sargus (n = 449) were caught along the Algerian coast between December 2005 and December 2006. Total length ranged from 12.2 to 34.6 cm, representing age classes between 0 and 10 years. Validity of the otolith readings for estimating age and growth was supported using the back‐calculation method. The von Bertalanffy growth parameters for all fish were calculated as: TL = 36.3 cm, k = 0.154 year⁻¹, t₀ = −0.488 year. The growth performance index (φ) showed a relatively slow growth of the local population. The length‐weight relationship showed an isometric growth (b = 2.98; r = 0.98). Subspecies Diplodus sargus sargus was characterized as being a proterandric hermaphrodite. Overall ratio of males to females was 1 : 1.4, with males predominant in the smaller size intervals and females in the larger ones. The reproductive season extended from January to May, with a March–April peak in spawning activity. Fifty per cent maturity of the tested cohort was reached at a total length of 20.2 cm for males and 20.0 cm for females.     

Isolation and characterization of simple repeat sequences from the yellow fin sea bream Acanthopagrus latus (Sparidae)

We isolated DNA fragments containing various repetitive elements from the genome of a sea bream Acanthopagrus latus. Sequence analysis indicated that two fragments have particularly interesting features. Fragment AL87 contained a tetranucleotide repeat and a quasipalindromic sequence. Sequence comparison suggested that AL87 may be a part of a gene encoding a serine/threonine protein kinase, and that the quasipalindrome is situated at the junction of an intron and an exon. Moreover, the quasipalindrome is conserved in several other fishes, even though it has the potential to form a stem-loop structure at the splicing site. Fragment AL79 contained a minisatellite sequence made up of six 30-bp units in tandem. DNase I sensitivity assays and statistical analyses showed the repeat region to be flexible when subjected to bending stress. In addition, atomic force microscopic imaging of AL79 showed the presence of highly curved (kinked) segments flanking the repeat region. The structural features of these repetitive elements may be key factors facilitating the amplification of the repeats.     

Comparison of UV-B tolerance between wild and hatchery-reared juveniles of red sea bream (Pagrus major) and black sea bream (Acanthopagrus schlegeli)

The amount of ultraviolet (UV)-B radiation reaching the sea surface has increased due to ozone depletion. Several laboratory studies have highlighted the negative impacts of UV radiation on fish using hatchery-reared specimens. However, potential differences in UV tolerance between wild and hatchery-reared fish have been given little consideration. Wild and reared juveniles of red sea bream and black sea bream were exposed to one of four different UV-B radiation levels (1.8; 1.1; 0.4; 0?W/m²) for 4?h. Survival rate was measured every 2?h for a period of 24?h (red sea bream) or 48?h (black sea bream) following exposure. Wild and reared juvenile red sea bream were characterized by similar survival rate, with survival declining to almost 0?% 24?h after exposure at the 1.1 and 1.8?W/m² levels. In black sea bream, wild individuals showed significantly higher survival than reared fish in levels 1.1 and 1.8?W/m². Melanophore density was also measured since melanin absorbs UV radiation. Wild black sea bream showed higher melanophore density compared to reared individuals, while no such difference was observed in red sea bream. We conclude that wild black sea bream juveniles acquire higher UV tolerance partly by increasing melanophore density through exposure to UV radiation. Our results indicate that the predicted impacts of UV radiation on fish populations solely based on experimentation with hatchery-reared specimens may be overestimated for some species.     

Age,growth, reproduction and feed of longnosed skate,Dipturus oxyrinchus (Linnaeus, 1758) in Saros Bay,the north Aegean Sea

The age, growth, reproduction, and feeding of longnosed skate (Dipturus oxyrinchus) were studied using 179 specimens from the Saros Bay (North Aegean Sea) between March 2005 and December 2007. Composition was 49.7% females and 50.3% males. Total length of females ranged from 14.9 to 100 cm (disc width, 9.8–65 cm), and of males from 15.2 to 86.5 cm (disc width, 10–57.5 cm). Total length‐weight and disc width‐weight relationships are described by the equations W = 0.0008*TL^3.35 and W = 0.0043*DW^3.29, respectively. The age data, derived from vertebrae readings, were used to estimate the growth parameters of the von Bertalanffy equation: L_∞ = 256.46 cm, K = 0.04 year^?1, t₀ = ?1.17year. The maximum age was 9 years. Males matured at 64–65 cm (disc width, 43.5 cm) and females at 82–83 cm TL (disc width, 53 cm). The stomach contained mainly Parapenaus longirostris, IRI: 93.47%.     

Age and growth of black seabream Acanthopagrus schlegelii (Sparidae) in Hong Kong and adjacent waters of the northern South China Sea

Age and growth of the black seabream Acanthopagrus schlegelii (family Sparidae) from the northern South China Sea (NSCS) were studied by reading growth rings in sectioned sagittal otoliths. Ring formation frequency was determined to be annual by using marginal increment analysis. The von Bertalanffy growth function parameters were estimated as: L_∞ = 43.7 cm L_S; K =0.22 year; t₀ = ?1.59 years. Functional males are significantly younger than functional females, with sexually transitional individuals between the modal ages of males and females supporting protandry in this species. Males become sexually mature within 1 year and 50% age at sex change is at 2 years. The maximum age recorded for both males and females sampled was 9 years which is lower than for conspecifics elsewhere and may reflect high fishing pressure in the study area when compared with conspecifics in other areas or could reflect latitudinal effects. Otolith mass was significantly and positively related to age, providing a cheap and quick alternative method for approximating age. Acanthopagrus schlegelii is a relatively fast‐growing and rapidly maturing species attaining a similar asymptotic length to conspecifics. A need for fishery management is indicated to protect both young juveniles and older adults, especially females, to increase reproductive output and safeguard fishery production.     

Feeding habits of the gilthead seabream (Sparus aurata) from the Ria Formosa (southern Portugal) as compared to the black seabream (Spondyliosoma cantharus) and the annular seabream (Diplodus annularis)

The feeding habits of Sparus aurata L., Diplodus annularis L. and Spondyliosoma cantharus L. in the Ria Formosa (southern Portugal) lagoon system were studied using three simple methods (frequency of occurrence, numeric percentage and percentage weight) and a composite index [index of relative importance (IRI)]. The Ivlev index was used to evaluate diet selectivity, while the Schoener overlap index was used to compare diets, and diet diversity was characterized by the Simpson index. The diets of the three species consist of a wide variety of food organisms, nevertheless S. aurata seems to be the most specialized. No significant dietary overlap was found, with S. aurata preferentially selecting gastropods and bivalves, while S. cantharus preferentially selected a wide variety of crustaceans and D. sargus a wider array, including crustaceans, gastropods and bivalves.     

黑鲷的胃排空率

在实验室内,18℃条件下测量了体重在 2 0～40g的黑鲷的胃排空率,并用 3种数学模型拟合了黑鲷的排空率.结果表明,3种模型都能很好地拟合实验数据,但通过统计学分析发现不论是用湿重还是用干重表示胃含物,线性模型都拟合得最好.用湿重表示时模型为Y=1.14-0.06t(r²=0 82,p<0.001);而用干重表示时模型为Y=1.36-0.07t(r²=0.62,p<0.001).实验还得出体重20～40g的黑鲷在 18℃的胃排空率为每小时排出摄入食物量的 6%～7%.     

Genetic integrity of black sea bream (Acanthopagrus schlegeli) sperm following cryopreservation

Although semen cryopreservation has been applied successfully in many fish species, extensive variation in post‐thaw semen quality exists between species and individuals. AFLP (amplified restriction fragment length polymorphism) is a powerful method for detecting DNA polymorphisms at the individual, population, and species levels. The method has been successfully applied to boars (Sus domestica, Suidae, Artiodactyla, Mammalia) to detect and evaluate differences in DNA sequences that correspond with semen integretiy after employing various freezing techniques. Freezing and thawing of semen has also an effect of selecting for freezing‐resistant (or intact) and eliminating non‐viable or defective sperm. Only the fully intact and functional sperm, despite potential compromise by adverse freezing and osmotic stresses, retain fertility after thawing. The objective of this study was to use AFLP to assess any genetic changes associated with the effect of employed cryo‐methodology on the genetic integrity of sperm of the black sea bream (Acanthopagrus schlegeli) under different cryopreservation treatments. The cryopreservation protocols had no significant effect on sperm motility or survival rate of fertilized ova regardless of using fresh (% motile sperm 89.6 ± 3.0; % embryonic survival rate 54.4 ± 2.9) and frozen‐thawed semen (% motile sperm 80.2 ± 2.0; % embryonic survival rate 51.8 ± 2.0). The post‐thaw sperm motility and survival rates were not significantly different among the sperm samples of the five black sea bream males examined. In the present study, the remaining black sea bream sperm that survive the cryopreservation limit the power of AFLP to trace the genetic markers which correlate with the differences in the sensitivity of sperm to cryo‐injury. It is also possible that point mutations outside the AFLP priming sites may not have been detected. More thorough investigations are needed to determine whether such DNA fingerprints would be found in fish species.