黄海中部近岸春夏季鱼卵、仔稚鱼群落结构特征

2013年4月下旬至7月上旬,采用浅水I型网垂直拖网的调查方式对黄海中部20m以浅海域(34°30'—35°30'N,119°20'—120°20'E)的鱼卵、仔稚鱼种类组成与数量分布进行了6个航次的综合调查。春夏季共采集鱼卵21种(未定种3种),共计2247粒,隶属于9科15属。仔稚鱼22种(未定种1种),共计286尾,隶属于13科17属。鱼卵优势种为日本鳀Engraulis japonicus、赤鼻棱鳀Thryssa kammalensis、江口小公鱼Stolephorus commersonnii、皮氏叫姑鱼Johnius belengerii和属Callionymus spp.。仔稚鱼优势种为大银鱼Protosalanx chinensis、白姑鱼Argyrosomus argentatus、日本鳀、赤鼻棱鳀和皮氏叫姑鱼。鱼卵丰度和分布与经度呈负相关、与SST呈正相关,但与其他环境因子如纬度、表层盐度(SSS)和水深等无显著相关性。仔稚鱼丰度和分布与上述环境因子均未表现出显著相关性。基于Bray-Curtis指数的聚类分析表明,鱼卵优势种包括集中分布于研究水域34°48'N以南海域(江口小公鱼、皮氏叫姑鱼和青鳞小沙丁Sardinella zunasi)、10m等深线以内(赤鼻棱鳀),以及北部水域(日本鳀和属)3种主要聚集类型;仔稚鱼优势种包括集中分布于34°48'N—35°12'N海域(赤鼻棱鳀和日本鳀)、连云港外海浅水区(白姑鱼、皮氏叫姑鱼和梭鱼Liza haematocheilus,以及南部水域(褐菖鲉Sebastiscus marmoratus和鲬Platycephalus indicus)3种主要聚集类型。研究结果揭示了黄海中部近岸海域鱼卵、仔稚鱼群落的时空分布格局动态,为科学认识环境变动下该海区渔业种群数量动态和资源变化提供了科学依据。     

Biometric studies on premetamorphic eel larvae ofAnguilla anguilla (Anguilliformes: Anguillidae) in comparison with younger developmental stages of the species

387 premetamorphic leptocephali of the familyAnguillidae caught off the west coast of Europe were examined taxonomically and compared with the youngest developmental stages of larvae ofAnguilla anguilla caught in the Sargasso Sea 1979 (Schoth, 1982). The total number of myomeres and the number of myomeres up to the third, opistonephritic blood vessel present features of this species which are significantly different from those of the larvae ofAnguilla rostrata and do not change during the whole larval phase. A combination of these two biometric features enables an infallible species identification of the AtlanticAnguilla larvae at all developmental stages. The number of predorsal and preanal myomeres, the preanal length and features of the head cannot be used for a distinction ofAnguilla larvae. One larva, 68.7 mm long, with 107 myomeres, and 44 myomeres to the opistonephritic blood vessel represents the hitherto southernmost record of anA. rostrata larva in the eastern North Atlantic.     

Spatio-temporal variability of ichthyoplankton and its relationship with oceanographic conditions at the shelf break off Chilean Patagonia (43°S–51°S)

Larval fish composition and abundance have been studied in fjords of south Patagonia. However, the ichthyoplankton of the adjacent shelf and slope waters of the Pacific Ocean, which is an important spawning and nursery ground for demersal fishery species (e.g. austral hake and Patagonian grenadier), remains largely unknown. To compare ichthyoplankton occurrence with environmental conditions in August 2013 and 2014 (austral winter), two bio-oceanographic cruises were carried out between 43° and 51°S. Conductivity, temperature and depth (CTD) data and ichthyoplankton samples were collected. The highest frequency of occurrence (FO) was observed for eggs of lightfish Maurolicus parvipinnis (84 and 91% FO in 2013 and 2014, respectively) and larvae of the myctophid Lampanyctodes hectoris (60 and 94% FO, respectively). Ichthyoplankton composition and abundance varied significantly between years, and richness varied from 10 (2013) to 18 taxa (2014). Only larval L. hectoris showed a significant increase in abundance during the winter of 2014. Water column temperature and salinity were significantly different between years; the water was warmer and saltier in 2013. Canonical Correspondence Analysis detected positive relationships between temperature and salinity with egg abundance and larval distribution of Merluccius australis. The highest abundance of eggs of M. australis was found at ～6–10°C, mainly off south Guafo Island. Additionally, ichthyoplankton from the shelf-break area off south Patagonia showed a wider latitudinal distribution in the winter of 2014 than in 2013.     

The occurrence and abundance of plants with extrafloral nectaries, the basis for antiherbivore defensive mutualisms, along a latitudinal gradient in east Asia

Abstract. The occurrence and abundance of indigenous plants with extrafloral nectaries was evaluated within local communities and regional floras along a north to south gradient from tundra in northeastern Russia (64–70°N) through temperate types in eastern Russia and Korea to subtropical vegetation in the Bonin Islands (26–27°N) south of Japan. Moving from tundra to subtropical vegetation, there is a pattern of increasing abundance of extrafloral bearing plants as a function of total plant cover (from 10.25 to 40.18%), number of species per sampled area (from 0.11 to 1.13/100 m), and proportion of species within regional floras (from 0.32 to 7.46%). There were some plants with extrafloral nectaries in all communities but their abundance varied greatly, c. 1–25% in the four northern latitudes and c. 7–70% in the subtropical region. Ants, the primary mutualists associated with plants bearing extrafloral nectaries, have a similar pattern of increasing abundance (species richness, nest density, and colony size) along the same north–south latitudinal gradient.     

长江口水域夏季鱼卵和仔稚鱼年间变化

基于2005年、2008年、2009年和2011年8月(夏季)在长江口水域(30°30'—31°45'N,121°15'—123°10'E)4个航次的浮游生物拖网资料,分析了长江口水域鱼卵和仔稚鱼的种类组成、数量分布特征及其年间变化。结果表明:4个航次采集的鱼卵和仔稚鱼鉴定到种的种类有17种,隶属于8目13科,以鲈形目种类最多,11种,其次是鲱形目,5种,其他各目种类均小于5种;种类数存在明显年间差异,2005年种类数最多(鱼卵3种,仔稚鱼8种),其次是2009年和2011年,2008年种类数最少(鱼卵1种,仔稚鱼5种)。优势种年间更替明显,长蛇鲻(Saurida elongata)、虾虎鱼(Gobiidae spp.)和中华小公鱼(Stolephorus chinensis)在2005年是优势种,2008年优势种为鳀鱼(Engraulis japonicus),2009年优势种为鳀鱼、寡鳞飘鱼(Pseudolaubuca engraulis)、虾虎鱼等,2011年虾虎鱼和小公鱼(包括小公鱼属未定种Stolephorus spp.和中华小公鱼Stolephorus chinensis)成为优势种。2005年鱼卵和仔稚鱼数量分布的密集区在嵊泗列岛附近水域,2008年鱼卵和仔稚鱼出现较少,未出现明显的数量密集区;2009年鱼卵数量较少,仔稚鱼数量较多,密集区主要分布在在长江口以外123°E附近水域;2011年鱼卵主要分布在在长江北支口门外附近水域,仔稚鱼在调查区内分布相对均匀。     

Heat coma as an indicator of resistance to environmental stress and its relationship to ocean dynamics in the sea skaters,Halobates (Heteroptera: Gerridae)

Abstract The tolerance to temperature increase was tested for Halobates individuals collected during two cruises in the western tropical Pacific Ocean (MR‐06‐05‐Leg 3, December 21, 2006–January 12, 2007, 0°N‐8°N; KH‐06‐02‐Leg 5, August 18–31, 2006, 12°N–17°N). High temperature coma experiments were conducted on adults and 5th instar larvae. On average, H. sericeus (distributed in the wide latitude zone of 5°N–40°N), H. germanus (distributed in the moderate latitude zone of 0°N–35°N) and H. micans (distributed mainly in the lower latitudes around the equator) were on average paralyzed at 35.6°C (SD: 0.89), 32.9°C (SD: 2.17) and 31.6°C (SD: 2.60), respectively (P= 0.035). According to the current dynamics during the cruise, the colony of H. sericeus at one station (5°N 137°E) may have been transferred from the northern area of 14°N by three currents (North Equatorial Current, Mindanao Current and North Equatorial Counter Current) to the area of 5°N 138°E. Extremely high heat resistance was shown by the adults of H. germanus in the sea area around the equator. Dynamic current and air movements in this area around the equator, that is a “warm seawater pool”, could be hypothesized to be related to the high resistance to heat shown in this study.     

Occurrence and abundance of three larval codlet species (Bregmacerotidae, Teleostei) in the Southwest Atlantic Ocean (12–22°S)

There are still only a few studies related to Bregmacerotidae larvae in Brazil, although these larvae are frequently collected in oceanic ichthyoplankton samples. Thus this study analyzes the occurrence and abundance of Bregmaceros larvae along the Brazilian central coast and describes larval characteristics. During three oceanographic cruises samples were collected between the Real River (12°S) and the São Tomé Cape (22°S). Oblique hauls were conducted from a maximum depth of 200 m, using bongo nets of 330‐ and 500‐μm mesh size. Among the 951 bregmacerotids collected, three species were identified corresponding to 89%Bregmaceros atlanticus, 8%Bregmaceros cantori and 3%Bregmaceros n. sp. B. atlanticus was widely distributed along the study area and was more frequent in stations situated beyond the 200‐m isobath; this species was more abundant during the winter, showing a peak of density between Vitória and the São Tomé Cape (355 larvae per 10 m²). Bregmaceros cantori densities were very similar during the three cruises; the highest value (25.6 larvae per 10 m²) was recorded during the winter and higher concentrations were observed in neritic stations along the 200‐m isobath. Bregmaceros n. sp. was rare in collections made during the three cruises; it was concentrated along the Bahia coast (12–18°S), and was more frequent in stations situated in the oceanic region. Bregmaceros atlanticus varying from 2.0 to 6.0 mm and Bregmaceros n. sp. larvae varying from 3.0 to 6.0 mm were present in all cruises, indicating that they spawn year‐round. Bregmaceros cantori did not show a distribution pattern among the different length classes, probably associated with the fact that this species has a coastal distribution.     

Length–weight relationships of three fish species from Kerala waters,south‐west coast of India

Length–weight relationships (LWRs) of three fish species: Scomberomorus commerson, Alepes vari, and A. kleinii were estimated from Kerala waters, south‐west coast of India. Fish were captured between June 2016 and June 2017 by various gears such as ring seine (8–26 mm mesh size), trawl (30–40 mm cod end mesh size), hook and line (hook number VI–XII), smaller mesh sized drift gill net (26–90 mm) and larger one (120–170 mm) for bigger size fishes. Fish were collected on weekly basis from Cochin Fisheries Harbour (Lat. 09°56′327″N, Long. 76°15′764″E), Munambam Fisheries Harbour (Lat. 10°10′965″N, Long. 76°10′258″E), Kalamukku (Lat. 09°59′924″N, Long. 76°14′564″E) and Chellanam (Lat. 09°47′950″N, Long. 76°16′551″E). All LWRs were significant with r² values ranged from 0.944 to 0.996 and b values ranged from 2.722 to 3.021 (p < .001). In addition, this study provides the information on LWRs and new maximum size for Alepes vari and A. kleinii.     

Distribution of leptocephali of the freshwater eels,genus <Emphasis Type="Italic">Anguilla</Emphasis>, in the waters off west Sumatra in the Indian Ocean

A research cruise was conducted in the eastern Indian Ocean off west Sumatra, Indonesia, in June 2003 to learn about the spawning and larval ecology of the tropical freshwater eels of the genus Anguilla in the region. A total of 43 anguillid leptocephali were collected during the cruise and they were genetically identified as 41 Anguilla bicolor bicolor, 1 Anguilla marmorata, and 1 Anguilla interioris. A. bicolor bicolor leptocephali were 44.1–55.5 mm TL and most of them were at the fully grown stage. Reexamination of the historical data of Jespersen (1942) also suggested a relatively low abundance of small size leptocephali (<40 mm) of this species off west Sumatra. Although the study area has long been considered to be a spawning site of A. bicolor bicolor, the distributions of leptocephali from the two surveys and the patterns of ocean currents in the region suggest the possibility that the main spawning area of this species is located farther offshore.     

Host instar suitability and life-history parameters under different temperature regimes of Necremnus artynes on Tuta absoluta

Necremnus artynes is native to the Mediterranean region where it has been observed in greenhouses parasitising Tuta absoluta on tomato. In this study, we evaluated the suitability of the different instars of T. absoluta as hosts for N. artynes and the life-history traits of N. artynes at three different temperature regimes (20, 25 and 30°C) on third instar T. absoluta larvae infesting tomato. N. artynes females preferred third instar T. absoluta larvae for oviposition, whereas host-feeding was significantly higher on the second instar larvae. Duration of life stages was no different between sexes but was affected by temperature, being significantly reduced as temperature increased. Pre-imaginal survival also decreased with temperature and the percentage of females was ca. 70% under all temperature regimes. Adult longevity was 1.5-fold significantly greater at 25°C compared to 30°C with no differences between 20 and 25°C. Fecundity was estimated at 36.3±7.80, 51.8±10.65 and 52.1±10.03 eggs/female and host-feeding at 59.5±8.50, 71.6±12.07, 51.4±7.89 hosts/female at 20, 25 and 30°C, respectively, although these differences among temperatures were not significant. However, oviposition and feeding rate were significantly higher at 30 and 20°C, respectively. The estimated intrinsic rate of increase (r _m) was significantly higher as temperature increased from 20 to 30°C and it was greater than those reported for T. absoluta on tomato, indicating the potential of N. artynes to control this pest.     

Fecundity and sexual maturity of the coral Siderastrea siderea at high latitude along the Florida Reef Tract,USA

Siderastrea siderea is one of the most abundant corals at high latitude shallow sites along the Florida Reef Tract (25°–27°N). This species is able to tolerate wide seawater temperature fluctuations and sedimentation stress, but its reproductive status at high latitudes and under marginal environmental conditions is poorly understood. The objectives of this study were to evaluate the reproductive potential of S. siderea along a latitudinal gradient (25°–27°N) and to determine if sexual maturity occurs in small (<12.0 cm) S. siderea colonies. Samples of coral tissue were collected in 2007, 2008, and 2009 at three sites along the latitudinal gradient and were processed for histological analysis. Oocyte size, volume, and abundance were used to calculate fecundity. Results showed that fecundity decreased with increasing latitude and that oocyte volume was the major contributing factor to this variation. Mature oocytes were observed in S. siderea colonies at sizes as small as 1.1 cm in diameter. The ability of S. siderea to reach fertility at high latitude areas suggests this species is able to reproduce under marginal environmental conditions; however, reduction in oocyte size could increase local retention of larvae. The presence of mature oocytes in small colonies suggests that stress can reduce somatic growth and shift sexual maturity to smaller colony sizes.     

Poleward increase in feeding efficiency of leafminer Stigmella lapponica (Lepidoptera: Nepticulidae) in a latitudinal gradient crossing a boreal forest zone

Damage to plant communities imposed by insect herbivores generally decreases from low to high latitudes. This decrease is routinely attributed to declines in herbivore abundance and/or diversity, whereas latitudinal changes in per capita food consumption remain virtually unknown. Here, we tested the hypothesis that the lifetime food consumption by a herbivore individual decreases from low to high latitudes due to a temperature-driven decrease in metabolic expenses. From 2016 to 2019, we explored latitudinal changes in multiple characteristics of linear (gallery) mines made by larvae of the pygmy moth, Stigmella lapponica, in leaves of downy birch, Betula pubescens. The mined leaves were larger than intact leaves at the southern end of our latitudinal gradient (at 60°N) but smaller than intact leaves at its northern end (at 69°N), suggesting that female oviposition preference changes with latitude. No latitudinal changes were observed in larval size, mine length or area, and in per capita food consumption, but the larval feeding efficiency (quantified as the ratio between larval size and mine size) increased with latitude. Consequently, S. lapponica larvae consumed less foliar biomass at higher latitudes than at lower latitudes to reach the same size. Based on space-for-time substitution, we suggest that climate warming will increase metabolic expenses of insect herbivores with uncertain consequences for plant–herbivore interactions.     

The effect of rainfall on tick challenge at Kyle Recreational Park,Zimbabwe

The effect of rainfall pattern on tick challenge was investigated at Kyle Recreational Park, Zimbabwe, from 1991 to 1992 using drag and removal plot methods to sample environmental tick density. The abundance of adults and nymphs of the brown ear-tick Rhipicephalus appendiculatus and larvae of the bont tick Amblyomma hebraeum was positively correlated with monthly rainfall, whereas no relationship with rainfall was revealed for larval R. appendiculatus, adults of the red-legged tick R. evertsi, or larvae of the blue tick Boophilus decoloratus. A comparison between 1991 (490 mm rainfall) and the drought year of 1992 (161 mm) revealed significant differences in the abundance of R. appendiculatus, A. hebraeum, and B. decoloratus. During the wet season, R. appendiculatus adults were 2–3 time more numerous in the environment during the higher rainfall year of 1991. A. hebraeum larval abundance exhibited a similar pattern to that of R. appendiculatus adults, but B. decoloratus larvae were more abundant in the drought year of 1992 during both the wet and dry seasons. Comparable tick abundance data collected at Kyle during the above-average rainfall years of 1975–1977 (mean = 1029 mm) were compared with tick challenge during the below-average rainfall years of 1991–1992 (mean = 326 mm). In grassland sand habitat and all habitats combined R. appendiculatus adults, nymphs, and larvae were much more abundant during the high rainfall years. In contrast, larvae of B. decoloratus were more numerous during the drier years. A. hebraeum larvae were also more abundant during the drier years. The strong positive correlation of adult R. appendiculatus abundance with rainfall and the coincidence of increased adult tick challenge with increased rainfall indicates that adult R. appendiculatus tick burden on hosts would be heaviest during the wet season and high rainfall years.     

Occurrence of Ayu (<Emphasis Type="Italic">Plecoglossus altivelis</Emphasis>) larvae in northern Vietnam

The early life history of Ayu (Plecoglossus altivelis) was investigated in the Kalong and Tien Yen River systems, northern Vietnam, which is probably the most southern distribution locality for this species, during the period of November 2010 to February 2011. A total of 248 larvae were captured in the Kalong, and none were collected in the Tien Yen. There was little difference in development between the Kalong larvae and those of P. a. altivelis and P. a. ryukyuensis. Temperatures and salinities when the larvae were collected ranged from ca. 12 to 21°C and from ca. 3.5 to 30 psu. The preflexion to flexion larvae (primarily preflexion with yolk, 5.2–12.9 mm BL) occurred in the central current from December to February, with a peak abundance in early January. The flexion to postflexion (primarily postflexion, 14.1–23.8 mm BL) larvae occurred in the bank waters from early January to late February. The larval occurrence in the Kalong was 1–2 months later than for P. a. altivelis in Japan and P. a. ryukyuensis in the Ryukyu Islands, probably because of the delay until a reasonable photoperiod for the start of spawning in the lower latitudinal region. The larvae were never collected from the sea, where the temperatures were lower than in the river and estuary in January and February, unlike in Japan.     

Growth and mortality of larval Myctophum affine (Myctophidae,Teleostei)

The growth and mortality rates of Myctophum affine larvae were analysed based on samples collected during the austral summer and winter of 2002 from south‐eastern Brazilian waters. The larvae ranged in size from 2·75 to 14·00 mm standard length (L_S). Daily increment counts from 82 sagittal otoliths showed that the age of M. affine ranged from 2 to 28 days. Three models were applied to estimate the growth rate: linear regression, exponential model and Laird–Gompertz model. The exponential model best fitted the data, and L₀ values from exponential and Laird–Gompertz models were close to the smallest larva reported in the literature (c. 2·5 mm L_S). The average growth rate (0·33 mm day^?1) was intermediate among lanternfishes. The mortality rate (12%) during the larval period was below average compared with other marine fish species but similar to some epipelagic fishes that occur in the area.     

Cyclomorphosis in Daphnia lumholtzi induced by temperature

• 1 Cyclomorphosis is a well known phenomenon in Daphnia that involves a regular, seasonal, or induced change in body allometry. Long helmets and tail spines were induced in laboratory cultures of Daphnia lumholtzi with temperature of 31 °C as the proximal cue (temperature of locally occurring peak abundance in Kentucky Lake). The effect was greater in embryos than juveniles or adults exposed to the temperature cue.
• 2 The temperature cue appears to have a threshold value (animals cultured at 25 or 28 °C did not develop elongated helmets or spines). The helmet and spine length receded both with D. lumholtzi kept at a constant 31 °C temperature and when water temperature was decreased.
• 3 The induced helmet in this experiment (0.66 mm, 1.0 mm animal) was significantly longer than values reported in the literature for induction by planktivorous fish kairomones (0.25 mm, 1.2 mm animal). The strong response to a proximal cue of temperature may require the second weaker chemical cue for maintenance. It is suggested that a synergistic explanation with two cues may be more appropriate for cyclomorphosis induction and maintenance in Daphnia lumholtzi that could be tested with further studies.

     

Vulnerability of larval white perch,Morone americana,to fish predation

Synopsis The vulnerability of white perch, Morone americana, larvae to yearling bluegill, Lepomis macrochira, predators was examined in relation to larval size, nutritional condition and relative abundance of alternative prey. Short-term (15 min) predation trials were conducted in 381 tanks in the laboratory. Larval vulnerability was measured as the proportion of larvae killed and the proportion of successful attacks per predator in each 15 min trial. No significant differences in vulnerability were apparent among larvae regardless of feeding history at sizes < 6 mm SL. At larval lengths > 6 mm SL, size of larvae was the crucial determinant of their vulnerability. Percentage of larvae killed in 15 min was nearly 100% at sizes < 6 mm SL, decreased to 30% at a length of 12.0 mm SL and dropped to 18% at 14.0 mm SL. Larvae initially feeding at low food levels for 2–4 d exhibited decreased growth of 13–25% over the first 3 wks of life, and simulations based on laboratory results indicated that these growth deficits could result in 5- to 68-fold decreases in survivorship at 38 days after hatching (DAH). The relative abundance of alternative prey also had a pronounced effect on mortality of larvae. A 10-fold increase in alternative prey (Daphnia magna) abundance decreased bluegill predation rates on white perch larvae by 10–20%, while a 100-fold increase in Daphnia density decreased larval mortality by 75–90%.     

Seasonal variations in biomass, abundance and composition of zooplankton in the subarctic waters north of Iceland

The seasonal variations in biomass, abundance and species composition of zooplankton in relation to hydrography and chlorophyll a were studied in the subarctic waters north of Iceland. The sampling was carried out at approximately monthly intervals from February 1993 to February 1994 at eight stations arranged along a transect extending from 66°16′N–18°50′W to 68°00′N–18°50′W. The mean temperature at 50 m depth showed a clear seasonal pattern, with lowest water temperatures in February (∼1.1°C) and the highest in July (∼5.4°C). The spring growth of the phytoplankton began in late March and culminated during mid-April (∼7.0 mg Chl a m⁻³). Both the biomass and the abundance of total zooplankton were low during the winter and peaked once during the summer in late May (∼4 g m⁻² and ∼38,000 individuals m⁻²). A total of 42 species and taxonomic groups were identified in the samples. Eight taxa contributed ∼90% of the total zooplankton number. Of these Calanus finmarchicus was by far the most abundant species (∼60% of the total zooplankton). Less important groups were ophiuroid larvae (∼9%), Pseudocalanus spp. (∼8%), Metridia longa (∼4%), C. hyperboreus (∼3%), Acartia longiremis (∼2%), chaetognaths (∼2%) and euphausiid larvae (∼2%). The dominant copepods showed two main patterns in seasonal abundance: C. finmarchicus, C. hyperboreus and C. glacialis had one annual peak in numbers in late May, while Pseudocalanus spp., M. longa and A. longiremis showed two maxima during the summer (July) and autumn (October/November). Ophiuroid larvae and chaetognaths (mainly Sagitta elegans) peaked during the middle of July, while the number of euphausiid eggs and larvae was greatest from May to July. The succession in population structure of C. finmarchicus indicated its main spawning to be in April and May, coincident with the phytoplankton spring bloom. A minor spawning was also observed sometime between August and October. However, the offspring from this second spawning contributed only insignificantly to the overwintering stock of C. finmarchicus. Received: 12 September 1997 / Accepted: 1 March 1998     

Taxonomic studies on the 0-group eel larvae (Anguilla sp.) caught in the Sargasso Sea in 1979

More than 2000 0-group larvae (5.0–30.0 mm long) of both AtlanticAnguilla species were examined taxonomically. With regard to the total number of myomeres inA. rostrata andA. anguilla, an average difference between the two species of 6 to 8 myomeres was found in all size groups. 31 specimens (i.e. 1.76 %) exhibited 111 myomeres. The position of the last vertical blood vessel and the number of preanal myomeres turned out to be statistically different in both species; however, these differences cannot be used for species identification. The regression line for the position of the last vertical blood vessel according to the total number of myomeres indicates that individuals with a total of 111 myomeres may beA. anguilla. Measurements of total lengths revealed highly significant differences between the larvae of both eel species. It can be concluded that, on the average,A. rostrata ( ) hatched about two weeks beforeA anguilla ( ). On the other hand, results obtained from the biggestA. rostrata larvae (29.5 mm) andA. anguilla larvae (23.5 mm) make a spawning ofA. rostrata likely two months beforeA. anguilla, when findings from hatching experiments withA. japonica are taken as a basis. There is no difference in the relative length of the intestine in eitherAnguilla species.