Fishery and growth of Aphia minuta off Majorca island

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Life cycle of the pelagic goby Aphia minuta (Pisces: Gobiidae)

Reproductive aspects of the transparent goby Aphia minuta (n=2977, 14-45 mm total length (TL)) were studied in Majorcan waters, western Mediterranean, during the fishing season (December to April) from 1985 to 1993. Male:female sex ratio was 1:1. Size at first maturity was 38 mm TL for females and 34 mm TL for males. Oocyte size-frequency distribution indicated that A. minuta is a single spawner. Fecundity of A. minuta ranged from 935 to 2648 oocytes. The breeding season extended from December to April with a peak in March. After a single reproduction at 5-6 months of age, most of the specimens disappeared from the fishing areas. Recruitment to the fishing area occurred in late December and early January (14-24 mm TL, age 2-3 months). On the other hand, the hatch date back-calculated from the age in days and the date of capture of individuals of A. minuta during the fishing season, indicated a spawning peak in autumn (September-October), six months after the peak of observed spawning. Schools of A. minuta were detected by acoustic methods, during the fishing season (winter-spring) in fishing areas (5-40 m depth), principally inside bays, and during the rest of the year (summer and autumn) in deeper areas (40-90 m), outside bays, with water temperatures between 13 and 16ºC and a high seasonal productivity in each depth range. Therefore, we propose that A. minuta has two annual cohorts in the western Mediterranean, corresponding to two main spawning in spring and autumn, respectively. Life history pattern indicated that we only know the winter cohort resulting from the autumn spawning. Meanwhile the summer cohort (spring spawning) grows and reproduces in deeper areas not being targeted by the fishery. Indirect validation is provided from information from other areas. The relevance of the life cycle is discussed in relation to fishery managementPublicado

An attempt to determine variability of RNA/DNA ratios during Dicentrarchus labrax larval development

RNA and DNA content of seabass (Dicentrarchus labra.x) larvae were determined from day 10 to day 60 after hatching in an aquaculture facility. Our results show a two-phase modulation of the RNA/DNA ratio throughout seabass larvae development. From day 10 after hatching there is an increase in the RNA/DNA ratio reaching maximal values at day 30 of age. Then, the RNA/DNA ratio decreased reaching minimal values at day 60 after hatching. These results are consistent with a high rate of protein synthesis during the first 30 days of seabass development compared with the rest of the developmental period studied. The results are compared with that of otolith growth carried out for the same species larvaeAPROXIMACIÓ A LA DETERMINACIÓ DE LA VARIABILITAT DE LA RELACIÓ DNA/RNA DURANT EL DESENVOLUPAMENT LARVAL DEL LLOBARRO Dicentrarchus labrax. S'ha determinat el contingut de DNA (àcid desoxiribonucleic) i de RNA (àcid ribonucleic) en larves de llobarro (Dicentrarchus labrax) d'edats compreses entre 10 i 60 dies de vida, procedents d'una planta de cultiu. Els resultats obtinguts mostren dues fases diferenciades de desenvolupament d'aquestes larves, basades en la relaci6 RNA/DNA avaluada. S'observa un augment de la proporci6 de RNNDNA des del dia 10 fins el dia 30 de vida, per a decréixer a continuació, trobant els valors mínims en les larves de 60 dies de vidaPublicado

Three small-scale fisheries based on the island of Majorca (NW Mediterranean)

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Diet of larval albacore Thunnus alalunga (Bonnaterre, 1788) off Mallorca Island (NW Mediterranean)

These are the first data on the feeding of larval albacore (Thunnus alalunga Bonnaterre, 1788) in the Mediterranean. Specimens were gathered from day-time bongo-hauls conducted over the SW Mallorcan (Balearic Islands) shelf-slope. Ninety eight percent of 101 individuals ranging from 2.65 to 9.4 mm standard length (SL) contained 1 to 15 prey items per gut. Mean number of prey/gut was 3.55 ± 2.19 (SD). A positive correlation was found between larval SL and the number of prey/gut. The analysis of frequency of occurrence (F), numerical frequency (N), weight frequency (W) and the Index of Relative Importance (IRI) showed a dominance of copepodites and nauplii in the smallest size-class. As larvae grew, cladocerans and Calanoida copepodites dominated the diet, and cladocerans and copepodites were important in F, N and W. Piscivory was observed after notochord flexion and was important in terms of W. A positive correlation between mean prey size and both SL and lower jaw length (LJL) was observed. The niche breadth (S) did not vary with LJL, but the raw prey size range did. Larger copepodites, the absence of nauplii and the incorporation of fish larvae and a larger number of cladocerans in the diet accounted for the increase in mean prey size through increased larval size.DIETA DE LAS LARVAS DE ALBACORA THUNNUS ALALUNGA (BONNATERRE, 1788) EN AGUAS DE MALLORCA (MEDITERRÁNEO NW). – Se ofrecen los primeros datos sobre la dieta de las larvas de albacora (Thunnus alalunga Bonaterre, 1788) en el Mediterráneo. Los especímenes se obtuvieron de pescas diurnas con bongo sobre la plataforma-talud al SW de Mallorca (Islas Baleares). El 98% de 101 individuos de entre 2.65 y 9.4 mm de longitud estándar (LE) contuvieron entre 1 y 15 presas por digestivo. La media de presas por larva fue de 3.55 ± 2.19 (DE), existiendo una correlación positiva entre el número de presas en el tubo digestivo y la LS. Los índices de frecuencia de ocurrencia (F), frecuencia numérica (N), frecuencia en peso (W) y el Índice de Importancia Relativa (IRI) mostraron un predominio de copepoditos y nauplius en larvas pequeñas, disminuyendo en importancia a lo largo del crecimiento en detrimento de cladóceros y copepoditos de Calanoida, que fueron importantes en F, N y W. Se observó piscivoría, importante en W, a partir de la flexión de la notocorda. Se detectó una correlación positiva entre el tamaño medio de las presas y tanto la LS como la longitud de la maxila (LJL) de las larvas. La amplitud del nicho alimentario (S) no varió con la LJL, aunque el rango total del tamaño de las presas sí lo hizo. El aumento de talla de los copepoditos, la desaparición progresiva de mauplius y la incorporación de larvas de peces y más cladóceros explica el aumento de la talla media de las presas a lo largo del crecimiento larvario.Versión del editor1,006

Reproductive strategies of common dentex Dentex dentex: management implications

The common dentex Dentex dentex is an iconic endangered species in the Mediterranean, where it is a target species that is sought after for small-scale, recreational and spearfishing fisheries. The reproductive biology of D. dentex in the natural environ¬ment is poorly known; therefore, the reproductive strategy of the species was assessed through a combination of reproductive traits and growth characteristics (estimated from length-at-age data), the size/age of sexual maturity and the energetic dynamics. A total of 358 wild fish, ranging in total length (LT) from 19 to 84.7 cm, was sampled at Mallorca Island (Western Mediterranean) from March 1996 to June 1999. The sex ratio was skewed towards females (1.361); however, the length composition was not different between sexes (p = 0.551). Three young immature individuals (< 28 cm LT, 0.8% individuals) were rudimentary hermaphrodites, offering support for classification as a late gonochoristic species. The age composition, determined based on the sagittal otolith, ranged from 0 to 26 years (yr). The von Bertalanffy growth function did not differ between sexes (F = 2.58, p = 0.762): L∞ =76.581 cm, K = 0.127 yr-1, t0 = -2.335 in a combined function. The maturity ogives for size and age showed that females achieved 50% maturity at 34.922 cm LT and 3.3 yr, and males, at 33.812 cm LT and 2.5 yrs. The onset of annual ripening took place in December, whereas vitellogenesis occurred from February to April. The spawning peak was in April and May for both males and females. A generalised linear model (GLM) showed that female size did not significantly affect the spawning season, whilst the seasonal component affected both the onset and end of spawning (GLM, p < 0.005). The gonadosomatic index (IG), hepatosomatic index (IH) and relative condition index (KR) varied significantly with the reproductive season for females, and IG varied for males. The microscopic observation of the gonads showed that fecundity is likely determinate, with an asynchronous oocyte development before spawning and a clear ovarian bimodal organization after the onset of spawning. The oocyte density variance of 85% was explained by the oocyte diameter, which also offered support for the trait of determinate fecundity. Female weight explained 84% of the observed variance for fecundity. Liver storage seemed to be the primary source of energy for maturity, which suggests a combination of capital and income breeding. The results suggested a reproductive strategy of type A, with balanced trade-offs be¬tween survival, growth and reproduction. At present, no management measures are being directed to D. dentex; herein, we suggest a minimum landing size of 35 cm LT to ensure a higher proportion of larger fish to preserve the stockVersión del editor0,568

Validation of daily increment deposition in otoliths: age and growth determination of Aphia minuta (Pisces: Gobiidae) from the NW Mediterranean

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Age and growth of blue-mouth, Helicolenus dactylopterus (Osteichthyes: Scorpaenidae) in the western Mediterranean

Helicolenus dactylopterus was studied from 15 bottom trawl cruises carried out between 1991 and 1997 along the Iberian Mediterranean coast. Age and growth of this species were determined for two different areas, the Alboran Sea and the Balearic Sea, characterised by distinct oceanographic and geomorphological conditions. The length (TL), weight (TW), and sex of 3093 individuals were recorded, and sagittal otoliths were collected in subsamples selected to cover the size distribution of both sexes in each area. Marginal increment analysis of specimens between 1 and 4 years old suggested that a single annulus was formed each year. The location of the first annulus was also validated by means of daily growth increments in the otoliths. The fish length range was between 3 and 36 cm in the Alboran Sea and between 2 and 33 cm in the Balearic Sea, which corresponded to individuals between 0 to 30 years old and 0 to 24 years old, respectively. However, 50 and 70% of the studied population in each area were between 0 and 3 years of age. The growth parameters obtained from the age–length relationships showed higher differences between sexes than between areas. In both areas, the maximum age observed and the predicted lengths of males were greater than those of females. The von Bertalanffy growth equation was TL=27.1(1−exp(−0.12(t+2.65))) for females and TL=32.3(1−exp(−0.09(t+3.31))) for males in the Alboran Sea, and TL=27.0(1−exp(−0.16(t+1.62))) for females and TL=32.5(1−exp(−0.10(t+2.62))) for males in the Balearic SeaPublicado