Embryo developmental events and the egg case of the Aleutian skate Bathyraja aleutica (Gilbert) and the Alaska skate Bathyraja parmifera (Bean)

Embryo development events were correlated with egg-case changes for the Aleutian skate Bathyraja aleutica and the Alaska skate Bathyraja parmifera . Yolk absorption underwent two phases: that of steady absorption during early development and that of rapid yolk absorption during the final development stages. Total length ( L _T) for 50% of the pre-hatching embryos egg-case jelly disappearance was 92·04 mm (range 81–102 mm) and 99·36 mm (range 81–100 mm) for B. aleutica and B. parmifera , respectively, allowing the inner chamber to open to seawater flow. The tail filament underwent three phases of growth: rapid elongation during early development (<100 mm embryo L _T), stasis of tail filament length during the remainder of embryo development and rapid absorption soon after hatching. Complete tail filament development coincided with the disappearance of egg-case jelly. Clasper buds first developed at embryos >70 mm L _T for both species and the sex ratio was 1:1 well before hatching. Egg cases that were devoid of an ova or developing embryo were c. 5·0 and 6·5% of the egg cases examined for B. aleutica and B. parmifera , respectively. Measurements showed that egg cases containing only egg jelly were smaller in both width and length than those possessing an ova. Embryo stages were punctuated with distinct events that correlated with egg case changes controlling the internal environment of the developing embryo.     

First records of advanced embryos and egg capsules of Bathyraja skates from the deep north-eastern Atlantic

Five variously developed embryos [142–279 mm total length (L_T)] from egg capsules from the Porcupine Seabight, north-eastern Atlantic (1541 m depth) are used to establish the ontogeny and early life history of Bathyraja richardsoni. The capsules of this species and two half-formed ones from the shell glands of a large (1620 mm L_T) female Bathyraja pallida taken off Ireland (c. 1900 m depth) are described and illustrated. The varying degree of yolk sac absorption found in the B. richardsoni embryos is discussed in relation to hatching size and its seeming size independence over c. 20–50 mm within the embryos' total length range. The conservative variation in external morphology with development from advanced embryos to adults among such deep stenobathic Bathyraja skates is commented upon, as is the bathymetric segregation of adults from levels in which egg capsules are deposited and young develop.     

Skate Bathyraja spp. egg predation in the eastern Bering Sea

Predation on skate eggs by snails was examined for three skate species at seven nursery sites in three regions (north, middle and south) of the eastern Bering Sea. Mean predation levels were 6·46% for the Alaska skate Bathyraja parmifera , 2·65% for the Aleutian skate Bathyraja aleutica and 22·25% for the Bering skate Bathyraja interrupta . Predation levels were significantly higher at the middle and north sites than the south sites for all species combined. Predation levels decreased with increasing egg-case densities at all nursery sites, and the highest predation levels occurred where egg-case densities were very low. Predated egg-case density increased with increasing snail densities across all nursery sites examined. The Oregon triton Fusitriton oregonensis was the most abundant snail species at all nursery sites and displayed ability to drill holes in the egg case of B. parmifera. Holes left by predatory snails in egg cases of B. parmifera were significantly larger, and of different shape at the middle site compared to the south site. Holes in B. parmifera were also significantly larger than those in egg cases of B. interrupta across all sites examined. Egg cases of B. aleutica possess surface spines that cover the egg case and may inhibit predation by snails at a greater rate than that of the B. parmifera and B. interrupta , which have a smoother egg-case surface.     

Reproductive biology of skates, Bathyraja(Ishiyama), along the eastern Bering Sea continental slope

Eight Bathyraja skate species, Bathyraja aleutica, Bathyraja interrupta, Bathyraja lindbergi, Bathyraja maculata, Bathyraja minispinosa, Bathyraja parmifera, Bathyraja taranetzi and Bathyraja trachura, collected along the eastern Bering Sea continental slope were examined for reproductive features. The sex ratio for six of eight Bathyraja skate species studied was c. 1 : 1 with males dominating for B. interrupta and B. parmifera. Five of eight species examined, B. aleutica, B. lindbergi, B. parmifera, B. taranetzi and B. trachura approximately equalled or exceeded the maximum reported total length, L_T. Maximum L_T for three species (B. interrupta, B. minispinosa and B. parmifera) revealed that the largest individuals were males and that in three other species (B. lindbergi, B. maculata and B. trachura) both females and males grew to approximately the same size. Both females and males matured at approximately the same L_T for seven of eight species. Only female B. aleutica matured at a much larger size than males. All species matured within a narrow size range following a protracted juvenile stage and once mature these skates appeared to grow very little. First maturity for all species occurred at ≥80% of their maximum L_T. The number of oocytes did not significantly differ between the left and right ovary for any species. The total number of mature oocytes increased with L_T for six of eight species examined. The number of oocytes for one species, B. aleutica, increased in number until 145 cm L_T, then declined in those individuals greater in length. The egg cases of all species are described, of which four (B. lindbergi, B. parmifera, B. taranetzi and B. trachura) have never been previously reported. Evidence is presented that suggest skates may be limited to as little as one and as many as 13 spawning seasons, depending on the species, and that senescence may occur in older individuals.     

Age and growth of the striped mullet, Mugil platanus (Actinopterygii, Mugilidae), in a southwestern Atlantic coastal lagoon (37°32'S–57°19'W): a proposal for a life-history model

Species of Mugilidae are an important economic resource supporting several small communities in Argentina and Brazil through fishing. The growth parameters of the von Bertalanffy model, age limit ( t _0.95) and natural mortality ( M ) for the striped mullet ( Mugil platanus ) Günther, 1880, in the Mar Chiquita coastal lagoon (37°32'S–57°19'W) were estimated. These results constitute the first estimated values for the species as: L _∞ (cm) = 563.82; K (years⁻¹) = 0.30; t ₀ (years) = −0.057 (age groups 1–8); t _0.95 = 10.07 years and M  = 0.30. Moreover, a hypothetical model is proposed for the life history of the adult stock of M. platanus from the Mar Chiquita coastal lagoon based on CPUE data, environmental parameters, ovarian maturity stages, gonadosomatic indexes, the allometric growth coefficient b and deposition of hyaline or opaque rings in the otholiths. Mugil platanus is therefore regarded as a species of moderate to rapid growth rate, with a relatively low longevity and a high natural mortality rate, compared to other species of Mugilidae.     

Age, growth and mortality of the Mediterranean amberjack Seriola dumerili (Risso 1810) from the south-eastern Adriatic Sea

The age, growth and mortality of the Mediterranean amberjack Seriola dumerili (Risso 1810) were determined in 298 specimens collected in the south-eastern Adriatic Sea (Donji Molunat Bay) from 17 May to 26 June 1997. The total length ranged from 32.0 to 160.0 cm and weight from 0.5 to 46.5 kg. Ten age classes, ranging from 1° to 10° years were defined by scale readings. Mean total length and weight-at-age data were used to estimate the growth parameters of the von Bertalanffy equation: L _∞=174.6 cm, K =0.190, t ₀=–0.314; W _∞=79.01 kg, K =0.139 and t ₀=–0.746. The length–weight relationship was estimated at: W =0.000123 ×  L ^2.847. The overall sex ratio was 1 : 1.06 in favour of males. Total ( Z ) and natural ( M ) mortality were found to be 0.41 years⁻¹ and 0.30 years^–1, respectively. The exploitation ratio ( E =0.27) indicates that the fishing pressure on the Mediterranean amberjack was low in the investigated region.     

Chondrichthyan egg cases from the south-west Atlantic Ocean

Egg cases of 21 oviparous chondrichthyan species from the south-west Atlantic Ocean are described and compared. The catshark Schroederichthys bivius has a cigar-shaped egg case with curled tendrils only at the posterior end. Egg cases of the elephant fish Callorhinchus callorynchus are spindle-shaped with anterior and posterior tubular extensions and lateral flanges. The skate Amblyraja doellojuradoi presents medium-sized egg cases (71 mm in length) with a lateral keel extending to the first portion of the horns. The endemic skate species of the genus Atlantoraja have medium to large egg cases (69-104 mm in length) and present relatively large posterior horns. Egg cases of the genus Bathyraja have a medium size, 75-98 mm in length, and are characterized by a very similar morphology, a relatively smooth to rough surface case and posterior horns strongly curved inwards. Egg cases of the genera Dipturus and Zearaja are very large, 115-230 mm in length, and have a well-developed posterior apron. Despite the problematical identification of skates at species level, the egg capsules of the endemic genus Psammobatis are easily diagnosed; the capsules are small (25-53 mm in length), those of Psammobatis rutrum being the smallest known to date in the world. Egg cases of Rioraja agassizi have a medium size, 61-68 mm in length, relatively straight sides, a smooth surface and silky attachment fibres placed in the lateral keel next to each horn. Those of the genus Sympterygia are small to medium sized, 51-86 mm in length, and display the thickest lateral keel and the longest posterior horns among the skates of the world. Egg cases can be a useful tool for identifying species and egg-laying areas; therefore, a provisional key for the south-west Atlantic Ocean chondrichthyan capsules is presented.     

Population structure, growth and reproduction of roughhead grenadier on the Flemish Cap and Flemish Pass

Roughhead grenadier Macrourus berglax were collected during the Flemish Cap bottom survey (1991–2001, NAFO division 3M, depth of 200–720 m) and on commercial vessels (1998–2000, NAFO divisions 3L, M and N, depth of 700–1700 m). The abundance of roughhead grenadier, as well as their average size, increased with depth. Age and length composition of the catches showed clear differences between the sexes. The proportion of males in the catch declined in the larger length classes and there were no males in the largest length classes (25 cm). There were differences in the growth trajectories of the two sexes; both sexes grew similarly up to 9 years, but the male growth was slower thereafter. The pre-anal fin length at first maturity ( L _PA50) for roughhead grenadier females was 28·5 cm, whilst the age at 50% maturity was 15–16 years. Individual total fecundity varied between 8522 and 61 844 oocytes. Macrourus berglax had a prolonged life cycle and multi-aged population structure, with differences in growth and mortality between males and females, slow maturation and low fecundity.     

Biology of the salema, Sarpa salpa (L. 1758) (Pisces, Sparidae) from the middle-eastern Adriatic

Salema Sarpa salpa (Linnaeus, 1758), were caught in the middle-eastern Adriatic Sea from August to November 2004. Length range of the samples was between 10.3 and 43.9 cm, with mean values of 25.5 cm in males, 32.6 cm in females, and 11.4 and 20.2cm in immature and hermaphrodite specimens, respectively. Sex ratio (males : females) was 3.1 : 1. Males were observed up to 37 cm length. Hermaphrodites showed lengths between 18 and 21 cm. The species was characterized by protandric hermaphroditism. Size at sexual maturity was 20.6 cm (2 years old) for males. Total length-total weight relationship for the entire population is described by the parameters a  = 0.00893, and b  = 3.1055. Otolith age readings showed that the population consisted of 15 age groups (1–15 years), including a very high proportion of individuals 1–7 years old. The von Bertalanffy growth parameters were L _∞ = 33.11cm, k  = 0.514, and t ₀ = −0.392 years for males and L _∞ = 40.85cm, k  = 0.179, and t ₀ = −2.606 years for females. Survival rate of females ( S  = 0.870) was much greater than for males ( S  = 0.769).     

Effects of different incubation temperatures on the yolk‐feeding stage of Eupallasella percnurus(Pallas)

Embryos and yolk‐feeding larvae of lake minnow Eupallasella percnurus were reared at 13, 16, 19, 22 and 25° C with no access to external food. Time from egg activation to first embryonic movements, hatching, filling of swimbladder and final yolk resorption increased with decreasing temperature. At 13° C, c . 40% of larvae were unable to fill their swimbladder. The predicted lower temperature at which development and growth ceased (biological zero, t ₀) was the same for both processes, c . 7·5–10·5° C. There was no ontogenetic shift in the t ₀ value. Temperature coefficients for development ( Q _10dev.) ranged from 2 to 3 at 19–25° C, but were higher in hatched larvae at lower temperatures. Eggs of E. percnurus had a combination of small size, high hydration and low caloric value of fresh matter. Dry mass of larval tissue on yolk, percentage of dry matter in wet matter, and specific growth rate were maximized at 22 and 25° C. At 19–25° C, energy and matter contained in the initial eggs were converted to body tissue most efficiently. Temperatures from 22 to 25° C are considered optimal for E. percnurus embryos and yolk‐feeding larvae and are recommended for their indoor rearing.     

Maturity and spawning pattern of Sardinella aurita in relation to water temperature and zooplankton abundance off Ghana, West Africa

Studies on the maturity and spawning pattern of Sardinella aurita Valenciennes in relation to sea surface temperature (SST) and zooplankton abundance were carried out during the period 1986–91 in Ghanaian waters (West Africa). Both sexes exhibited synchronous seasonal maturation patterns. The mean length at first maturity occurred at approximately16.7 cm for males and 17.1 cm for females. The mean length at first maturity (L₅₀) increased in comparison with that observed in the 1970s. Three spawning seasons were identified: a major season which extends from July to October, and two minor seasons which occur in March and December. Significant correlations were found between the female gonadosomatic index and SST, between egg abundance and SST, and between egg abundance and zooplankton abundance. The SST seems to be an important factor in species maturation. There is a time lag between attainment of peak gonad maturation and onset of spawning. Spawning appears to commence in response to the start of the coastal upwelling which is characterised by a sharp decrease in SST and an increase in zooplankton abundance.     

Effect of Iysozyme concentration, heating at 90°C, and then incubation at chilled temperatures on growth from spores of non-proteolytic Clostridium botulinum

The heat treatment necessary to inactivate spores of non-proteolytic Clostridium botulinum in refrigerated, processed foods may be influenced by the occurrence of lysozyme in these foods. Spores of six strains of non-proteolytic Cl. botulinum were inoculated into tubes of an anaerobic meat medium, to give 10⁶ spores per tube. Hen egg white lysozyme (0–50 μg ml^-1) was added, and the tubes were given a heat treatment equivalent to 19·8 min at 90°C, cooled, and incubated at 8°, 12°, 16° and 25°C for up to 93 d. In the absence of added lysozyme, neither growth nor toxin formation were observed. A 6–D inactivation was therefore achieved. In tubes to which lysozyme (5–50 μg ml^-1) had been added prior to heating, growth and toxin formation were observed. With lysozyme added at 50 μg ml^-1, growth was first observed after 68 d at 8°C, 31 d at 12°C, 24 d at 16°C, and 9 d at 25°C. Thus, in these circumstances, a heat treatment equivalent to 19·8 min at 90°C was not sufficient, on its own, to give a 6–D inactivation. A combination of the heat treatment, maintenance at less than 12°C, and a shelf-life not more than 4 weeks reduced the risk of growth of non-proteolytic Cl. botulinum by a factor of 10⁶.     

Life-history traits of invasive bighead goby Neogobius kessleri (Günther, 1861) from the middle Danube River, with a reflection on which goby species may win the competition

Life history traits of an invasive population of bighead goby Neogobius kesslerei (Günther, 1861) from the middle Danube, including absolute and relative fecundity, egg size, number of spawning batches and size at first maturation, were examined and evaluated within an epigenetic context. Ripe bighead goby females attained 42.8–142.5 mm L _S, with absolute fecundities ranging from 669 to 5646 eggs (mean 2109 eggs), and relative fecundities of 61.6–174.0 eggs g⁻¹ body weight (mean 119.6 eggs). Egg diameters varied between 0.04 mm and 1.70 mm (mean = 0.57 mm). In the pre-spawning period there was no clear size distinction in eggs (0.12–1.45 mm; mean = 0.52 mm) in 34.1% of females; whereas in 65.9% of females, two egg size groups were distinguished: group I diameters of 0.06–0.85 mm (mean = 0.43 mm), and group II diameters of 0.55–1.70 mm (mean = 1.17 mm). Females with size-group II eggs at the beginning of the reproductive season were assumed to be ready to spawn and the others to be subsequent spawners. Bighead goby appears to be altricial compared to the round goby, although in both species a shift from highly precocial towards a less precocial life history was observed. These differences, affected by epigenetic mechanisms and resulting in alternative ontogenies, may have important implications for a species' potential success in novel environments, favouring the round goby over short time periods (several years) and bighead goby over longer periods of time (decades and longer).     

Exploring nursery sites for oviparous chondrichthyans in the Southwest Atlantic (36°S–41°S)

The aim of this paper was to explore egg-laying areas of oviparous chondrichthyans occurring in the northern part of the Southwest Atlantic Ocean (36°S–41°S) at between 50 and 200 metres depth and the Mar del Plata Canyon (from 200 to 3447?m). A total of 515 capsules were collected corresponding to 10 species. Four species accounted for 87.6% of the total catch: Psammobatis normani, Bathyraja macloviana, Amblyraja doellojuradoi and Bathyraja brachyurops. The remaining corresponded to Schroederichthys bivius, Psammobatis rudis, Zearaja chilensis, Bathyraja albomaculata, Psammobatis lentiginosa and Bathyraja sp. Most hauls were monospecific and relatively few hauls contained four or five species (southern part of the area, in sites located at 75 and 94–105?m depth). No egg capsules were recorded between 1712?m and 3447?m. Highest densities (>3000 capsules/km²) were mainly found between 39°46.2′ and 40°29.9′S from 85 to 105?m and they were also recorded near the Mar del Plata Canyon at 37°59.7′S and at 852?m. The highest value recorded was 12,326 capsules/km² (located at 40°18.9′S and 85.4?m). The highest densities for each of the most abundant species are discussed. The finding of high densities of egg cases near the Argentine shelf-break front indicates that many skate species use this area as a nursery site. The egg-laying areas explored here are the first reported sites of this kind in the Southwest Atlantic Ocean. Recognizing and protecting egg-laying habitats may be important steps to a long-term conservation of oviparous chondrichthyan populations.     

Age, growth, mortality and population structure of the oyster, Crassostrea madrasensis, in the Moheskhali Channel (southeastern coast of Bangladesh)

The population structure, age, growth, mortality and harvest intensity of the oyster Crassostrea madrasensis were examined in the Moheskhali Channel, Bangladesh between June 2003 and May 2004. The channel is a representative habitat for the area. C. madrasensis monthly length frequency data were analyzed using FiSAT software for estimating population parameters, including asymptotic length ( L _∝ ), growth co-efficient ( K ) and recruitment pattern to assess the status of the stock. Asymptotic length ( L∝ ) and growth co-efficient ( K ) were 20.88 cm and 0.35 year⁻¹, respectively. The growth performance index (φ') was calculated with 2.18. The growth pattern showed negative allometric growth ( b  < 3), with an asymptotic weight ( W _∝ ) of about 1124.6 g. The oyster attained an average length of 6.17 cm at the end of 1 year. Total mortality ( Z ) by length-converted catch curve was estimated at 1.78 year⁻¹, fishing mortality ( F ) at 0.77 year⁻¹, and natural mortality ( M ) at 1.01 year⁻¹. The exploitation level ( E ) of C. madrasensis was 0.43, while the maximum allowable limit of exploitation ( E _max) was 0.45 for the highest yield. The recruitment pattern was continuous, displaying a single major peak event per year. Habitat temperatures were 25.5–31.0°C (mean ± SD, 29 ± 1.62°C); salinity range was from 12.36 to 26.0 ppt (mean ± SD, 19.6 ± 4.7 ppt). The exploitation level (0.43) indicated that the oyster stock was exploited at almost maximum yield in this channel.     

Age, growth, sexual maturity and food composition of Sciaena umbra in the south-eastern Black Sea, Turkey

Studied were the age, growth, maturity and food composition of the brown meager, Sciaena umbra, caught off Trabzon, south-eastern Black Sea (Turkey) in 2002–2003. A total of 329 individuals was collected by spear fishing and hand nets. The thin sectioning method was used for aging the fish otoliths. Fitted von Bertalanffy growth parameters for all fish were: L _∞ = 51.14 (±1.19) cm, k  =   0.27 (±0.02) year⁻¹ and t ₀ = −0.93 (±0.07) year. This study revealed that S. umbra is a relatively slow-growing and long-lived species with a life span in excess of 18 years. Sexual maturity begins when they reach a length of about 15 cm. Lengths at which 50% of brown meagre become mature are 19.50 for males and about 22 cm for females. Spawning begins in June, when the temperature is approximately 18°C, and ends in August. Gut content analysis indicated that this species feeds mainly on crustaceans, then switches to fish as they grow. Sciaena umbra appears to be an apex predator in the upper littoral zone.     

Reproductive biology of the Alaska skate Bathyraja parmifera,with comments on an intersexual individual

A total of 1357 specimens of Alaska skate Bathyraja parmifera were collected in the eastern Bering Sea by fisheries observers and during scientific groundfish surveys from 2003 to 2005. Male and female gonads were examined for maturity stage and seasonal reproductive timing. Based on seasonal reproductive data, including the occurrence of egg cases, ovum size, ovum number, shell‐gland width and gonado‐somatic index, this species appears to reproduce continually throughout the year. Potential effects of maternal size upon the size and number of mature oocytes were also investigated, with total length having a significant, although weak, influence on both. Morphology of a single intersexual individual encountered during the collection period is also described.     

Reproduction of the sandpaper skate,Bathyraja kincaidii (Garman 1908) in the eastern North Pacific

The sandpaper skate, Bathyraja kincaidii, is commonly taken as bycatch in trawl fisheries off central California. The impact of fisheries exploitation on this population is unknown, however little is known about its biology, including its reproductive life history. To determine reproductive aspects of B. kincaidii, 506 individuals were collected from commercial trawls, museum collections, and monthly trawl and longline surveys conducted by the National Marine Fisheries Service. Males ranged from 112 to 635 mm TL, whereas females ranged from 113 to 610 mm TL. Males reach first maturity at 440 mm TL and at ~3 years, whereas females reach first maturity at 450 mm TL, approximately 1 year later. Size and estimated age at 50 % maturity were similar between sexes: 492 mm TL and 7.5 years for males and 467 mm TL and 7.1 years for females. Gonadosomatic index (GSI) and hepatosomatic index (HSI) values indicate a continuous reproductive cycle, with a seasonal peak in the summer and fall, and a resting period following egg case deposition.     

Sensitivity of wild and genetic sexing strain Ceratitis capitata to high-temperature disinfestation of Valencia oranges

Abstract:  The purpose of this research was to investigate post-harvest heat treatment of Valencia oranges as an effective disinfestation protocol (fast, no fruit damage) for the Mediterranean fruit fly Ceratitis capitata (Wiedemann). Forced high-temperature air was applied under the following conditions: (a) exposure to air temperature of 56°C, for fast increase of temperature in the interior of the fruit, (b) reduction in air temperature to 47°C when the fruit centre reached 47°C and (c) maintenance of fruits in the chamber for another 30 min. Relative humidity in the treatment chamber was kept between 50% and 65% during treatment. Forced air at 47°C applied for 30 min on eggs before hatch or late third instar larvae (the most heat-tolerant stages) resulted in complete kill. Egg and larval sensitivity to high temperature differed between a wild strain and a laboratory genetic-sexing strain based on white pupa mutation. In this strain males emerge from brown pupae and females from white pupae. In particular, mature eggs from the wild strain were significantly more temperature resistant than eggs from the laboratory strain. Exposure of Valencia oranges of a diameter of 7–7.5 cm to 56°C forced air for about 86 and 99 min was required to increase temperature to 47°C at 1.5 cm depth and the fruit centre respectively. Treated oranges showed no substantial peel or interior deterioration, or change in colour and taste when kept at 25°C and 50–60% RH for a period of up to 1 month following treatment. Treatment in 1% O₂ atmosphere, produced by flushing of CO₂ into the treatment chamber, resulted in about 1°C reduction in killing temperature and faster increase in temperature inside the fruit to a lethal level.