Ichthyoplankton community in the Columbia River plume off Oregon: effects of fluctuating oceanographic conditions

Ichthyoplankton samples were collected at approximately 2-week intervals, primarily during spring and summer 1999−2004, from two stations located 20 and 30 km from shore near the Columbia River, Oregon. Northern anchovy (Engraulis mordax) was the most abundant species collected, and was the primary species associated with summer upwelling conditions, but it showed significant interannual and seasonal fluctuations in abundance and occurrence. Other abundant taxa included sanddabs (Citharichthys spp.), English sole (Parophrys vetulus), and blacksmelts (Bathylagidae). Two-way cluster analysis revealed strong species associations based primarily on season (before or after the spring transition date). Ichthyoplankton abundances were compared to biological and environmental data, and egg and larvae abundances were found to be most correlated with sea surface temperature. The Pacific Decadal Oscillation changed sign (from negative to positive) in late 2002 and indicated overall warmer conditions in the North Pacific Ocean. Climate change is expected to alter ocean upwelling, temperatures, and Columbia River flows, and consequently fish eggs and larvae distributions and survival. Long-term research is needed to identify how ichthyoplankton and fish recruitment are affected by regional and largescale oceanographic proces

Activity in the pallial nerve of knobbed (Busycon carica) and channeled (Busycotypus canaliculatum) whelks recorded during exposure of the osphradium to odorant solutions

Adult horseshoe crabs (Limulus polyphemus) are the preferred bait in the U.S. east coast whelk pot fishery, but their harvest is being restricted because of severe population declines in the Chesapeake and Delaware bays. To identify other baits, the activity in the pallial nerve of whelks was determined during exposure of the osphradium to odorant solutions prepared from horseshoe crab eggs, horseshoe crab hemolymph, and hard clam (Mercenaria mercenaria) tissue. All three elicited significant responses; bait based on them may provide an alternative to the use of adult horseshoe crabs, although extensive behavioral testing remains to be done. Channeled whelk did not respond to molecular weight fractions (>3 kDa and <3 kDa) prepared from horseshoe crab egg odorant solutions but did respond when the molecular weight fractions were recombined. Whelks appear to have broadly tuned chemoreceptors and manufactured baits may need to mimic the complex mixture of odorants derived from natural sources.

Description of embryonic development of Atka mackerel (Pleurogrammus monopterygius)

Atka mackerel (Pleurogrammus monopterygius) is hexagrammid fish that inhabits the temperate and subarctic North Pacific Ocean and neighboring seas (Fig. 1). This highly abundant fish is a critically important prey species (Sinclair and Zeppelin, 2002; Zenger, 2004) that supports a directed commercial trawl fishery (Lowe et al., 2006). Atka mackerel is a demersal spawner and males provide parental care to eggs (Zolotov, 1993). During breeding periods, sexually mature males aggregate on the bottom at nesting sites where they establish territories (Lauth et al., in press). Sexually mature females periodically visit male nesting territories from July to October to spawn batches of demersal egg masses (McDermott and Lowe, 1997; McDermott et al., 2007). Individual nests may consist of multiple egg masses deposited by different females, and males defend nesting territories for a protracted period lasting from the time territories are being established until all eggs within the territory are completely hatched (Lauth et al., 2007). Knowledge about the timing of the reproductive cycle and the use of spawning habitat are important for understanding population structure and the dynamics of stock recruitment, which in turn are important factors in the management of Atka mackerel populations.

Diel variation in vertical distribution of an offshore ichthyoplankton community off the Oregon coast

We examined the diel ver-tical distribution, concentration, and community structure of ichthyoplank-ton from a single station 69 km off the central Oregon coast in the northeast Pacific Ocean. The 74 depth-stratified samples yielded 1571 fish larvae from 20 taxa, representing 11 families, and 128 fish eggs from 11 taxa within nine families. Dominant larval taxa were Sebastes spp. (rockfishes), Stenobra-chius leucopsarus (northern lampfish), Tarletonbeania crenularis (blue lan-ternfish), and Lyopsetta exilis (slender sole), and the dominant egg taxa were Sardinops sagax (Pacific sardine), Icichthys lockingtoni (medusafish), and Chauliodus macouni (Pacific viperfish). Larval concentrations generally increased from the surface to 50 m, then decreased with depth. Larval concentrations were higher at night than during the day, and there was evidence of larval diel vertical migration. Depth stratum was the most important factor explaining variability in larval and egg concentrations.

Changes in egg production of the western rock lobster (Panulirus cygnus) associated with appendage damage

Data collected during fish-ery-independent sampling programs were used to examine the impact of appendage damage (indicated by lost or regenerated legs and antennae) on the reproductive output of female western rock lobster (Panulirus cygnus). Most of the damaged females sampled had one (53%), two (27%), or three (13%) appendages that had been lost or that were regenerating. Appendage damage was associated with the reduced probability of a female developing ovigerous setae; and if setae were produced, with the reduced probability that females would produce more than one batch of eggs within a season. These effects were more pronounced as the number of damaged appendages increased. From data collected in 2002, it was estimated that the total number of eggs produced by mature females caught in the fishery was significantly reduced (P<0.001) by 3–9% when the impact of appendage damage was included.

Annual fecundity, batch fecundity, and oocyte atresia of Atka mackerel (Pleurogrammus monopterygius) in Alaskan waters

Annual potential fecundity, batch fecundity, and oocyte atresia were estimated for Atka mackerel (Pleurogrammus monopterygius) collected in Alaskan waters during 1993−94. Atka mackerel were assumed to be determinate spawners on the basis of decreasing fecundity after batch spawning events. Histological examination of the ovaries indicated that oocytes in the vitellogenic stage and higher had been spawned in the current spawning season. For an average female of 40 cm, potential annual fecundity was estimated to be 41,994 eggs, average batch size (i.e., batch fecundity) was estimated to be 6689 eggs, and there were 6.13 batches per spawning season. Atresia was estimated by examining postspawning specimens and was found to be substantial. The average amount of atresia for a 40-cm fish was estimated to be 11,329 eggs, resulting in an estimated realized fecundity of only 30,664 eggs and 4.64 batches of eggs per spawning season.

Abundance of adult horseshoe crabs (Limulus polylphemus) in Delaware Bay estimated from a bay-wide mark-recapture study

Estimates of the abundance of American horseshoe crabs (Limulus polyphemus) are important to determine egg production and to manage populations for the energetic needs of shorebirds that feed on horseshoe crab eggs. In 2003, over 17,500 horseshoe crabs were tagged and released throughout Delaware Bay, and recaptured crabs came from spawning surveys that were conducted during peak spawning. We used two release cohorts to test for a temporary effect of tagging on spawning behavior and we adjusted the number of releases according to relocation rates from a telemetry study. The abundance estimate was 20 million horseshoe crabs (90 % confidence interval: 13−28 million), of which 6.25 million (90% CI: 4.0−8.8 million) were females. The combined harvest rate for Delaware, New Jersey, Virginia, and Maryland in 2003 was 4% (90% CI: 3−6%) of the abundance estimate. Over-wintering of adults in Delaware Bay could explain, in part, differences in estimates from ocean-trawl surveys. Based on fecundity of 88,000 eggs per female, egg production was 5.5×1011 (90% CI: 3.5×1011, 7.7×1011), but egg availability for shorebirds also depended on overlap between horseshoe crab and shorebird migrations, density-dependent bioturbation, and wave-mediated vertical transport.

Hatching date, nursery grounds, and early growth of juvenile walleye pollock (Theragra chalcogramma) off northern Japan*

Walleye pollock (Theragra chalcogramma) is widely distributed in the North Pacific Ocean and plays an important role in coastal subarctic ecosystems. The Japanese Pacific population of this species is one of the most important demersal fishes for commercial fisheries in northern Japan. The population is distributed along the Pacific coast of Hokkaido and the Tohoku area (Fig. 1), which is the southern limit of distribution of the species in the western North Pacific. In Funka Bay, the main spawning ground for this population, pollock spawn from December to March (Kendall and Nakatani, 1992). Planktonic eggs and larvae are transported into the bay, where juveniles usually remain until late July when they reach 60−85 mm in total length (Hayashi et al., 1968; Nakatani and Maeda, 1987). These juvenile pollock then migrate from Funka Bay eastward to the Doto area off southeastern Hokkaido (Honda et al., 2004). Many studies on eggs, larvae, and juveniles of the species have been conducted in or near Funka Bay, but little information is available on the ecology of the early life stages in the Tohoku area. Hashimoto and Ishito (1991) suggested that eggs are transported from Funka Bay southward to the Tohoku area by the coastal branch of the Oyashio Current, but there has been no study to verify this hypothesis.

Reprodução e parasitismo em Melanoides tuberculata (Müller, 1774) (Gastropoda, Thiaridae) da Vila do Abraão, Ilha Grande, Angra dos Reis, RJ

Melanoides tuberculata (Müller, 1774), molusco exótico límnico de origem afroasiática, foi registrado pela primeira vez na Vila do Abraão, Ilha Grande, Angra dos Reis, Rio de Janeiro, em 2005. Atua como primeiro hospedeiro intermediário de diversos trematódeos de importância médica. As populações são compostas majoritariamente por fêmeas partenogenéticas que possuem um marsúpio onde se desenvolvem os juvenis. Os objetivos foram verificar: a presença de machos; se existem flutuações na produção de ovos e juvenis ao longo do tempo; quando a maturidade sexual é atingida e, a existência de parasitos relacionando sua presença com o número de ovos e juvenis. Para a contagem de ovos e juvenis, foram utilizadas fêmeas coletadas bimestralmente de setembro/07 a outubro/10, separadas em quatro classes de tamanho, segundo o diâmetro da concha: Classe I: < 3mm; Classe II: 3 a 5,99mm; Classe III: 6 a 8,99mm; Classe IV: > 9mm. Separamos cinco fêmeas/classe, totalizando 20 fêmeas/coleta, exceto nas amostras de setembro/07 (16 exemplares), abril/09 (19 exemplares) e de abril/10 (13 exemplares), totalizando 348 fêmeas. Para observação dos parasitos, ovos e juvenis o teto da cavidade palial foi retirado e o marsúpio dissecado. Classificamos os juvenis em classes de acordo com o número de voltas: com menos de duas; com duas a quatro e com mais de quatro. Os dados foram analisados utilizando Excel e SYSTAT 12. Para a histologia da gônada e do marsúpio, utilizamos cinco exemplares coletados mensalmente de setembro/12 a fevereiro/13, de cada classe de tamanho, totalizando 20 espécimes/coleta, exceto em outubro/12, quando 16 espécimes foram usados, pois somente um espécime da Classe IV foi encontrado. Os espécimes foram fixados em formalina Millonig de Carson, descalcificados em EDTA, incluídos em parafina e corados em hematoxilina e eosina. Foram encontrados 16 machos. Quantificamos 24.694 ovos e 31.474 juvenis, com as seguintes médias: Classe I: 0 ovos e 0,31 juvenis; Classe II: 24,19 ovos e 47,56 juvenis; Classe III: 114,84 ovos e 155,78 juvenis; Classe IV: 146,76 ovos e 158,41 juvenis. O teste de Kruskal-Wallis mostrou que existe variação significativa no número de ovos e juvenis ao longo do ano (p < 0,01 para ambos) e entre o número de ovos e juvenis entre as diferentes classes de tamanho de concha (p <0,01 para ambos). Foram contabilizados 27.877 juvenis com menos de duas voltas, 3.251 juvenis com duas a quatro voltas e 346 juvenis com mais de quatro voltas. Dentre 348 fêmeas, 111 estavam parasitadas (32% do total) por Centrocestus formosanus (Nishigori, 1924). O Teste de Mann-Whitney, levando em consideração todas as fêmeas, demonstrou que fêmeas parasitadas apresentaram menor número de ovos e juvenis que as não parasitadas ( p<0,01). Excluindo as fêmeas da Classe 1, o resultado do teste foi o mesmo (p< 0,01). Concluímos que: a população de M. tuberculata da Vila do Abraão não é formada somente por fêmeas; as fêmeas se reproduzem o ano todo, pois foram encontrados ovos e juvenis em todas as coletas; que quanto maior a fêmea há mais ovos e, em média, há mais juvenis no marsúpio; que a maturidade sexual é alcançada com aproximadamente 3 mm de diâmetro de concha, devido a presença de ovócitos vitelogênicos tardios e, que o parasitismo afeta negativamente M. tuberculata, reduzindo o número de ovos e juvenis formados

Factors determining spawning success in Penaeus monodon Fabricius

Spawning success in relation to the size of spawner, clumping of eggs, percentage of spawning and frequency of spawning was studied in Penaeus monodon collected off Tamil Nadu, India. The results indicated positive correlation between the size of spawner and the fecundity and hatching percentage, but not the start of hatching. Hatching characteristics were influenced by clumping of eggs or abortive spawning; the greater the clumping, the longer the time taken for hatching, resulting in a lower hatching percentage. The start of hatching time increased when the frequency of spawning increased. Lower hatching rate was observed as the frequency of spawning increased.

River-based artificial propagation of the African catfish Clarias gariepinus: an option for the small fish farmer

A cheap method of propagating the African catfish, Clarias gariepinus, by incubating the fertilized eggs in a cage placed directly in a flowing river is described. Hatching ranged between 39 and 70%. This is not significantly different from the commonly used water recirculating flow through system. The economic advantages of the river hatching method are discussed with special emphasis on the rural fish farmers.

Demand for fish in Sub-Saharan Africa: the past and the future

The Sub-Saharan region of Africa accounted for only 5.5% of the world's demand for fish from 1989 to 1991, inspite of comprising 9% of the global population. This study was carried out to determine the future demand for fish in the Sub-Saharan region. Fish accounts for approximately 10% of animal protein consumed. It is prominent in the diet of the poor since cured and smoked fish is a cheaper source of protein than meat or eggs. The average per capita consumption in 1992 was about 8 kg compared to 30 kg globally. Fish is prominent in the diets of people near coastal areas and large inland water bodies and a total of 40% of fish consumed is freshwater fish. Consumption is rising in the coastal areas but falling inland, probably due to drought and overexploitation resulting in an inadequate supply. Aquaculture has not been widely adopted and does not contribute substantially to the region's supply. To determine future demand and trends, a regression analysis was carried out at the country level with FAO data on fish consumption from 1960 to 1992, using several proxies for disposable income, cost of fishery products, changes in tastes and national differences in the tradition of fish consumption. An aggregate increase in fish consumption of nearly 2.7% annually over the next few years was predicted with a strong correlation between increases in income, prices and population. Real income was a significant and positive determinant of fish consumption, even though consumption increaed more slowly than income. Given the high projected rate of population increase, the growth rate in overall fish consumption actually implies a reduction in per capita fish consumption of 0.31% annually. If technological progress can improve production and supply, aquaculture could have a significant impact on fish consumption in the region.

Some reproductive aspects of Chrysichthys nigrodigitatus (Lacépède) from Cross River, Nigeria

Between May and October 1990, fecundity, egg size and condition factor of Chrysichthys nigrodigitatus (Lacépède) in the Cross River, Nigeria, were studied. The fecundity (F) of this population varied from 3 046 eggs (total length, L=28.5 cm) to 28 086 eggs (L=64 cm). A mean relative fecundity of 231 eggs/cm or 13 eggs/g of fish was obtained for this population. The fecundity of this population can be estimated with the formula F=2.511 · L 2.30 or F=52.893 · W 0.78 , total length being in cm and weight (W) in g. The mean egg diameter of this population varied from 0.65 mm to 3.54 mm. Condition factor (CF) of the population varied from 0.24 to 1.34 with 0.977 as the mean; 52.8% had CF higher than the mean and 47% had CF above unity. Smaller fish in this population were in better condition than bigger ones. The egg size and condition factor obtained in this study are evidence that the Cross River population of C. nigrodigitatus can provide excellent broodstock.

Effect of different salinity levels on the fertilization and hatching of Heterobranchus bidorsalis

The success of induced spawning for the production of fish seed depends on many factors which affect hatchery conditions. This paper discusses the results of an investigation on the effects of six different levels of salinity on the fertilization and hatching of Heterobranchus bidorsalis eggs. The results indicate that spermatozoa of H. bidorsalis can survive under a wide range of saline concentrations, with survival increasing with an increase in salinity from 0 to 0.4% and then decreasing as the level of salinity increases. Survival was optimum of 0.4% saline concentration.

Reproductive biology of carpenter seabream (Argyrozona argyrozona) (Pisces: Sparidae) in a marine protected area

The carpenter seabream (Argyrozona argyrozona) is an endemic South African sparid that comprises an important part of the handline fishery. A three-year study (1998−2000) into its reproductive biology within the Tsitsikamma National Park revealed that these fishes are serial spawning late gonochorists. The size at 50% maturity (L50) was estimated at 292 and 297 mm FL for both females and males, respectively. A likelihood ratio test revealed that there was no significant difference between male and female L50 (P>0.5). Both monthly gonadosomatic indices and macroscopically determined ovarian stages strongly indicate that A. argyrozona within the Tsitsikamma National Park spawn in the astral summer between November and April. The presence of postovulatory follicles (POFs) confirmed a six-month spawning season, and monthly proportions of early (0−6 hour old) POFs showed that spawning frequency was highest (once every 1−2 days) from December to March. Although spawning season was more highly correlated to photoperiod (r = 0.859) than temperature (r = −0.161), the daily proportion of spawning fish was strongly correlated (r= 0.93) to ambient temperature over the range 9−22oC. These results indicate that short-term upwelling events, a strong feature in the Tsitsikamma National Park during summer, may negatively affect carpenter fecundity. Both spawning frequency and duration (i.e., length of spawning season) increased with fish length. As a result of the allometric relationship between annual fecundity and fish mass a 3-kg fish was calculated to produce fivefold more eggs per kilogram of body weight than a fish of 1 kg. In addition to producing more eggs per unit of weight each year, larger fish also produce significantly larger eggs.