Retention mechanisms of white perch (Morone americana) and striped bass (Morone saxatilis) early-life stages in an estuarine turbidity maximum: an integrative fixed-location and mapping approach

The small‐scale distribution and retention mechanisms of white perch (Morone americana) and striped bass (M. saxatilis) early‐life stages were investigated in the upper Chesapeake Bay estuarine turbidity maximum (ETM). Physical measurements and biological collections were made at fixed‐location stations within the ETM during three research cruises in 1998 and two in 1999. Results were compared with mapping surveys of physical properties and organism distributions above, within, and below the ETM. Physical conditions at the fixed stations differed markedly among cruises and between years due to differences in freshwater flow and wind. In each year, striped bass and white perch larval concentrations were highest in waters of salinity 1–4. Larvae were more abundant in the ETM region in 1998, a high‐flow year, suggesting that the ETM provides favorable nursery habitat when low salinity waters and the ETM coincide in high freshwater‐flow conditions. In 1998, the earliest pelagic life stages of fish larvae (eggs, yolk‐sac larvae) and the copepod Eurytemora affinis, an important prey of feeding larvae, apparently were retained in deep, landward‐flowing water within the salt front and ETM region. Statistical analyses indicated that distributions of white perch and striped bass post‐yolk‐sac larvae were associated with E. affinis distributions and suggested that retention of larval fish could result from tracking prey. Comparing fixed‐station and mapping approaches demonstrates the importance of sampling at different spatial scales within the ETM region and suggests that larvae are faced with trade‐offs between selecting zones of high retention or high visual‐feeding success.     

Growth of early juvenile winter flounder (Pseudopleuronectes americanus Walbaum)

Metamorphosis is a critical developmental stage in marine fish species, but mortalities are also elevated at the settling phase. Our objective was to evaluate the effects of different rearing systems and larval diets on survival, general condition and pigmentation of newly settled winter flounder (Pseudopleuronectes americanus) juveniles. At settlement, winter flounder juveniles were reared in two different types of tanks (plankton kreisel and rectangular raceway). The early juveniles were followed for 1 month and their condition was evaluated using biochemical indices. Juveniles did not show signs of fin rot and pigmentation was well developed, but they had different RNA/DNA ratios. This study highlights the fact that rearing conditions at the onset of the juvenile stage may be critical for successful juvenile production.     

Spatial distribution patterns of fish egg and larval assemblages in the lower reach of the Yangtze River: Potential implications for conservation and management

1. River fish diversity is threatened by anthropogenic environmental alteration to landscapes. The early life-history stages of fish play an important role in maintaining diversity and population recruitment and can be heavily influenced by landscape patterns. Information on temporal and spatial distribution patterns of fish eggs and larvae is also important for biodiversity conservation and management of fish resources.
2. The Yangtze River possesses a high diversity of fishes, including many commercially important species. The economy along the lower reach of the river is well developed, and most of the area is experiencing high pressure from human impacts. This section of the Yangtze River connects with the largest freshwater lake in China at the upstream end and flows into the estuary at the downstream end. These two landscape features are likely to have a significant impact upon the spatial distributions of fish egg and larval assemblages.
3. Environmental variables, fish eggs, and larval assemblages were sampled in three locations, at Hukou, Anqing, and Jingjiang, in the lower reach of the Yangtze River. The results suggest that the higher number of species and greater abundance in upstream sites reflect the critical function of connectivity of Poyang Lake with the river for fish recruitment in the lower Yangtze. The delayed bloom of larval fish, occurrence of estuarine species, and a lower species number and abundance of freshwater fish downstream reflect the influence of tidal intrusion from the estuary.
4. This study highlights the value of maintaining natural river–lakes connectivity in the Yangtze River as a conservation measure. The connected river–lake system should be designated as a priority area for fish resource protection in the lower reach of the Yangtze River. We recommend further measures to break down barriers between the river and other lakes and to restore the natural lateral connectivity of the floodplain ecosystem.

     

金属离子Ni2+和Co2+对卤虫孵化率和变态率的影响

在去除重金属离子的天然海水中添加不同浓度的Ni^2 和Co^2 进行养殖实验，研究了Ni^2 和Co^2 对盐卤虫（Artemia saline)孵化率及变态率的影响。在试验过程中保持温度（27℃）、盐度（30‰）以及pH(=8)恒定。结果表明：当海水中Ni^2 和Co^2 浓度分别为40μg/L和30μg/L时对旧金山湾卤虫的孵化最为有利，当Ni^2 浓度为40μg/L,Co^2 浓度为40μg/L-50μg/L时对其发育变态最为有利。从而得出结论：当海水中Ni^2 浓度在40μg/L范围左右时可促进卤虫的孵化及变态发育，当海水中Co^2 浓度为30μg/L-50μg/L范围内时可促进卤虫的生长发育。     

Effects of different diets on larval development in a peppermint shrimp (Lysmata sp. (Risso))

Currently, only a handful of marine ornamental species are commercially produced through aquaculture. In order for the marine aquarium industry to continue to grow, a diverse selection of cultured animals is required to offset wild collections. Long and variable larval durations are the major bottleneck for mass production of marine ornamental shrimp. Improving larval diet may reduce the larval duration and enhance the prospects of commercial aquaculture. A laboratory study was conducted to examine the effect of different diets on larval development and survival of the peppermint shrimp, Lysmata (gulf coast variety), a popular aquarium shrimp. The effect of three feeding regimes [Artemia alone (ART), ArteMac? alone (COMM) and Artemia in combination with ArteMac? (ART/COMM)] on survival and development were tested. Survival to zoea 5 for both ART and ART/COMM treatments was 99%, but only 62.5% for COMM treatment. ArteMac? alone treatment shrimp only survived to zoea 7. Survival to postlarvae for ART treatment (72.5%) was significantly lower (P<0.01) than those of treatment ART/COMM (80.5%). Larvae fed ART/COMM had significantly (P<0.01) shorter larval duration than larvae fed ART. Fourteen days after the first postlarva appeared, the rates of settlement (85.4% and 67.5% respectively) and survival (68.8% and 49.0% respectively) were significantly greater (P<0.01) for larvae fed the ART/COMM than those fed ART.     

Variation in sea lice infestation on Atlantic salmon smolts in Killary Harbour,West Coast of Ireland

Approximately 300 salmon smolts were stocked in each of four cages moored at various distances between an Atlantic salmon farm and a river system in Killary Harbour on the West Coast of Ireland. Samples of fish were taken from each of the cages on three occasions and examined for the presence of sea lice (Lepeophtheirus salmonis). Results from one-way ANOVA tests and a multiple comparison of the means of infection levels in the cages indicated that there was a significant difference between the infection levels in the cages on each of the sampling dates. Cage 1, positioned nearest the river, exhibited the highest levels of infection on the first sampling date and was highly significantly different (p 0.001) from the other three cages which showed no significant difference between each other. This situation was again repeated on the second sampling date. On the final sampling date, cage 4, positioned nearest the salmon farm, was highly significantly different (p 0.001) from the other three cages; cage 1 was significantly different (p 0.05) from cages 2 and 3 which showed no significant difference from each other.The population structure of the lice recovered from the smolts indicated that the lice settled in pulses rather than continuously over the trial period. The results are discussed in relation to the hydrography of Killary Harbour, the output of lice larvae from the farm, the impact that these may have on infestations in the inner area of Killary and probable areas of lice larval production.     

Distribution of jack mackerel (Trachurus japonicus) larvae and juveniles in the East China Sea, with special reference to the larval transport by the Kuroshio Current

Horizontal distribution patterns of jack mackerel (Trachurus japonicus) larvae and juveniles were investigated in the East China Sea between 4 February and 30 April 2001. A total of 1549 larvae and juveniles were collected by bongo and neuston nets at 357 stations. The larvae were concentrated in the frontal area between the Kuroshio Current and shelf waters in the upstream region of the Kuroshio. The abundance of small larvae (<3 mm notochord length) was highest in the southern East China Sea (SECS) south of 28°N, suggesting that the principal spawning ground is formed in the SECS from late winter to spring. Jack mackerel also spawned in the northern and central East China Sea (NECS and CECS, respectively), as some small larvae were also collected in these areas. In the SECS, the abundance of small larvae was highest in February and gradually decreased from March to April. The habitat temperature of small larvae in the SECS and CECS (20–26°C) was higher than that in the NECS (15–21°C), suggesting higher growth rates in the SECS and CECS than in the NECS. The juveniles (10‐ to 30‐mm standard length) became abundant in the NECS off the west coast of Kyushu Island and CECS in April and were collected in association with scyphozoans typical of the Kuroshio waters. However, juveniles were rarely collected in the SECS, where the small larvae were concentrated. Considering the current systems in the study area, a large number of the eggs and larvae spawned and hatched in the SECS would be transported northeastward by the Kuroshio and its branches into the jack mackerels’ nursery grounds, such as the shallow waters off the west coast of Kyushu and the Pacific coast of southern Japan.     

Transport of larval jack mackerel (Trachurus japonicus) estimated from trajectories of satellite-tracked drifters and advective velocity fields obtained from sequential satellite thermal images in the eastern East China Sea

Transport processes of jack mackerel (Trachurus japonicus) larvae in the waters off the west coast of Kyushu in the eastern East China Sea, have been investigated using satellite‐tracked surface drifters and consecutive satellite thermal images. Trajectories of drifters describe northward flows over the continental shelf, eastward flows of the Kuroshio south‐west of Kyushu, and a weak clockwise gyre off the west coast of Kyushu. In particular, the clockwise gyre causes the entrainment of jack mackerel larvae into the waters off the west coast of Kyushu. Consecutive satellite thermal images help to elucidate the northward warm water intrusion from the Kuroshio front south‐west of Kyushu. Particle trajectories using sea surface current fields computed with the Maximum Cross Correlation (MCC) technique also reveal that the transport of jack mackerel larvae into the nursery ground off the west coast of Kyushu caused by the anti‐cyclonic gyre and the warm streamers are an important process for successful recruitment.     

Embryonic development and larval and post‐larval growth of the tropical scallop Nodipecten (= Lyropecten) nodosus (L. 1758) (Mollusca: Pectinidae)

This work describes for the first time the embryonic development of the tropical scallop Nodipecten nodosus. Larval and post‐larval growth parameters and some characteristics of larvae shell morphology were also ascertained. The larvae were obtained from the induced spawning of a group of broodstocks under controlled laboratory conditions. After fertilization, larval cultivation was carried out in conical tanks at a temperature of 26–27 °C. Larval density was controlled as a function of larval growth to give 10, 5 and 3 larvae mL^?1 from days 1, 3 and 8 respectively. The larvae were nourished with a 1:1 mix of Isochrysis galbana (clone T‐ISO) and Chaetoceros gracilis in portions varying between 30 000 and 70 000 cells mL^?1. Expulsion of polar groups was observed 5 and 15 min after fertilization, whereas the first cellular division occurred after 30 min. The first gastrule ciliates and trocophore larvae were noted after 8 and 18 h had elapsed, respectively, whereas prodissoconch I, or D‐larvae, were discerned after 26 h. Subsequently, larvae with prodissoconch II or veliger‐conch appeared at 30 h. Larval development continued for 10–12 days, followed by metamorphosis, at an approximate length of 208–230 µm. The growth of the post‐larvae was evaluated for 9 days. Larval and post‐larval growth corresponded to the linear equations L = 71.85 + 10.85t, r² = 0.99, and L = 44.09 + 17.81t, r² = 0.94 respectively. Accordingly, larval morphology and size disparities are discussed with respect to other tropical pectinids.