Biology, Oceanography, and Fisheries of the North Pacific Transition Zone and Subarctic Frontal Zone: Papers from the North Pacific Transition Zone Workshop, Honolulu, Hawaii, 9-11 May 1988

In the past few years, large-scale, high-seas driftnet fishing has sparked intense debate and political conflict in many oceanic regions. In the Pacific Ocean the driftnet controversy first emerged in the North Pacific transition zone and subarctic frontal zone, where driftnet vessels from Japan, the Republic of Korea, and Taiwan pursue their target species of neon flying squid. Other North Pacific driftnet fleets from Japan and Taiwan target stocks of tunas and billfishes. Both types of driftnet fishing incidentally kill valued non-target species of marine life, including fish, mammals, birds, and turtles. In response to public concerns about driftnet fishing, government scientists began early on to assemble available information and consider what new data were required to assess impacts on North Pacific marine resources and the broader pelagic ecosystem. Accordingly, a workshop was convened at the NMFS Honolulu Laboratory in May 1988 to review current information on the biology, oceanography, and fisheries of the North Pacific transition zone and subarctic frontal zone. The workshop participants, from the United States and Canada, also developed a strategic plan to guide NMFS in developing a program of driftnet fishery research and impact assessment. This volume contains a selection of scientific review papers presented at the 1988 Honolulu workshop. The papers represent part of the small kernel of information available then, prior to the expansion of cooperative international scientific programs. Subsequent driftnet fishery monitoring and research by the United States, Canada, Japan, Korea, and Taiwan have added much new data. Nevertheless, this collection of papers provides a historical perspective and contains useful information not readily available elsewhere. (PDF file contains 118 pages.)

Report on Marine Mammal Unusual Mortality Event UMESE0501Sp: Multispecies Mass Stranding of Pilot Whales (Globicephala macrorhynchus), Minke Whale (Balaenoptera acutorostrata), and Dwarf Sperm Whales (Kogia sima) in North Carolina on 15-16 January 2005

On 15-16 January 2005, three offshore species of cetaceans (33 short-finned pilot whales, Globicephala macrorhynchus, one minke whale, Balaenoptera acutorostrata, and two dwarf sperm whales, Kogia sima) stranded alive on the beaches of North Carolina. The pilot whales stranded near Oregon Inlet, the minke whale in northern North Carolina, and the dwarf sperm whales near Cape Hatteras. Live strandings of three species in one weekend was unique in North Carolina and qualified as an Unusual Mortality Event. Gross necropsies were conducted on 16-17 January 2005 on 27 pilot whales, two dwarf sperm whales, and the minke whale. Samples were collected for clinical pathology, parasitology, gross pathology, histopathology, microbiology and serology. There was variation in the number of animals sampled for each collection type, however, due to carcasses washing off the beach or degradation in carcass condition during the course of the response. Comprehensive histologic examination was conducted on 16 pilot whales, both dwarf sperm whales, and the minke whale. Limited organ or only head tissue suites were obtained from nine pilot whales. Histologic examination of tissues began in February 2005 and concluded in December 2005 when final sampling was concluded. Neither the pilot whales nor dwarf sperm whales were emaciated although none had recently ingested prey in their stomachs. The minke whale was emaciated; it was likely a dependent calf that became separated from the female. Most serum biochemistry abnormalities appear to have resulted from the stranding and indicated deteriorating condition from being on land for an extended period. Three pilot whales had clinical evidence of pre-existing systemic inflammation, which was supported by histopathologic findings. Although gross and histologic lesions involving all organ systems were noted, consistent lesions were not observed across species. Verminous pterygoid sinusitis and healed fishery interactions were seen in pilot whales but neither of these changes were causes of debilitation or death. In three pilot whales and one dwarf sperm whale there was evidence of clinically significant disease in postcranial tissues which led to chronic debilitation. Cardiovascular disease was present in one pilot whale and one dwarf sperm whale; musculoskeletal disease and intra-abdominal granulomas were present in two pilot whales. These lesions were possible, but not definitive, causal factors in the stranding. Remaining lesions were incidental or post-stranding. The minke whale and three of five tested pilot whales had positive morbillivirus titers (≥1:8 with one at >1:256), but there was no histologic evidence of active viral infection. Parasites (nematodes, cestodes, and trematodes) were collected from 26 pilot whales and two dwarf sperm whales. Sites of collection included stomach, nasal/pterygoid, peribullar sinuses, blubber, and abdominal cavity. Parasite species, locations and loads were within normal limits for free-ranging cetaceans and were not considered causative for the stranding event. Gas emboli lesions which were considered consistent with or diagnostic of sonarassociated strandings of beaked whales or small cetaceans were not found in the whales stranded as part of UMESE0501Sp. Twenty-five heads were examined with nine specific anatomic locations of interest: extramandibular fat, intramandibular fat, auditory meatus, peribullar acoustic fat, peribullar soft tissue, peribullar sinus, pterygoid sinus, melon, and brain. The common finding in all examined heads was verminous pterygoid sinusitis. Intramandibular adipose tissue reddening, typically adjacent to the vascular plexus, was observed in some individuals and could represent localized hemorrhage resulting from vascular rete rupture, hypostatic congestion, or erythrocyte rupture during the freeze/thaw cycle. One cetacean had peracute to acute subdural hemorrhage that likely occurred from thrashing on the beach post-stranding, although its occurrence prior to stranding cannot be excluded. Information provided to NMFS by the U.S. Navy indicated routine tactical mid-frequency sonar operations from individual surface vessels over relatively short durations and small spatial scales within the area and time period investigated. No marine mammals were detected by marine mammal observers on operational vessels; standard operating procedure for surface naval vessels operating mid-frequency sonar is the use of trained visual lookouts using high-powered binoculars. Sound propagation modeling using information provided to NMFS indicated that acoustic conditions in the vicinity likely depended heavily on position of the receivers (e.g., range, bearing, depth) relative to that of the sources. Absent explicit information on the location of animals meant that it was not possible to estimate received acoustic exposures from active sonar transmissions. Nonetheless, the event was associated in time and space with naval activity using mid-frequency active sonar. It also had a number of features in common (e.g., the “atypical” distribution of strandings involving multiple offshore species, all stranding alive, and without evidence of common infectious or other disease process) with other sonar-related cetacean mass stranding events. Given that this event was the only stranding of offshore species to occur within a 2-3 day period in the region on record (i.e., a very rare event), and given the occurrence of the event simultaneously in time and space with a naval exercise using active sonar, the association between the naval sonar activity and the location and timing of the event could be a causal rather than a coincidental relationship. However, evidence supporting a definitive association is lacking, and, in particular, there are differences in operational/environmental characteristics between this event and previous events where sonar has apparently played a role in marine mammal strandings. This does not preclude behavorial avoidance of noise exposure. No harmful algal blooms were present along the Atlantic coast south of the Chesapeake Bay during the months prior to the event. Environmental conditions, including strong winds, changes in upwelling- to downwelling-favorable conditions, and gently sloping bathymetry, were consistent with conditions which have been correlated with other mass strandings. In summary, we did not find commonality in gross and histologic lesions that would indicate a single cause for this stranding event. Three pilot whales and one dwarf sperm whale had debilitating conditions identified that could have contributed to stranding, one pilot whale had a debilitating condition (subdural hemorrhage) that could have been present prior to or resulting from stranding. While the pilot and dwarf sperm whale strandings may have had a common cause, the minke whale stranding was probably just coincidental. On the basis of examination of physical evidence in the affected whales, however, we cannot definitively conclude that there was or was not a causal link between anthropogenic sonar activity or environmental conditions (or a combination of these factors) and the strandings. Overall, the cause of UMESE0501Sp in North Carolina is not and likely will not be definitively known. (PDF contains 240 pages)

Abundance and Distribution of Ichthyoplankton along an Inshore-Offshore Transect in Onslow Bay, North Carolina

The distribution and abundance of ichthyoplankton was investigated from November 1979 to March 1980 along a transect from coastal to continental slope waters in Onslow Bay, North Carolina. Representatives of 66 families were collected; 24 of which were tropical families, a category that also includes families of typically oceanic and deep-sea fishes. Larvae of tropical species were collected in coastal and shelf waters, demonstrating the intrusion of Gulf Stream waters onto the continental shelf. From December through March, frontal waters that separated cold open-shelf surface waters from warm Gulf Stream surface waters were observed. Higher abundances of fish larvae were sometimes, but not consistently, associated with frontal waters. A great diversity of taxa was collected in offshore waters, and densities of larvae were low in coastal waters; low densities were attributed to gear selectivity rather than low larval abundance. Larvae of commercially and recreationally important estuarine-dependent species, especially Leiostomus xanthus and Micropogonias undulatus, were dominant components of the ichthyoplankton. Representatives of the families Bothidae, Clupeidae, Gadidae, Gonostomatidae, Myctophidae, Ophidiidae, and Sparidae were also important components of the ichthyoplankton. Larvae of species representing two strikingly different life history types-mesopelagic and estuarine-dependent frequently cooccurred.(PDF file contains 32 pages.)

Marine Ranching: Proceedings of the Eighteenth U.S.-Japan Meeting on Aquaculture Port Ludlow, Washington, 18-19 September 1989

Female reproduction in penaeid shrimp is carefully regulated by several different endocrine factors. Their precise modes of action have not yet been fully elucidated. Three endocrine factors, each representing a different chemical class of hormones, have been investigated in the penaeid shrimp Sicyonia ingentis in our laboratory: ecdysteroids, vitellogenesis-inhibiting hormone (VIH) , and methyl farnesoate (MF). Ecdysteroids (the steroid molting hormones of arthropods; predominantly 20-hydroxyecdysone), are initially present in low levels (<10 ng/mg) in shrimp embryos. As development of the embryos nears time of hatch, the ecdysteroid levels increase to approximately 150 ng/ mg, indicating that they may be of embryonic origin and involved in embryonic development. An assay was developed for shrimp VIH, which presumably is a protein. Delay of onset of the next reproductive cycle was observed following injection of sinus gland extracts into shrimp that had previously had their eyestalks removed. A photoaffinity analog was synthesized for the putative shrimp reproductive hormone MF-a terpenoid. This analog, farnesyl diazomethyl ketone (FDK) , was used to demonstrate the presence of specific binding proteins for MF in shrimp hemolymph. (PDF file contains 136 pages.)

On the physical and biological oceanography near the entrance of the Gulf of California, October 1966-August 1967

ENGLISH: A study of the temporal and spatial distribution of larval tunas and the concomitant oceanic conditions was made in cooperation with the Direccion General de Pesca e Industrias Conexas of Mexico. Field work consisted of eight hydrographic cruises made from October 1966 through August 1967 near the entrance of the Gulf of California. From January through April, surface currents were southerly at velocities up to 20 cm/sec; currents in June were variable in direction and mostly less than 10 cm/sec; by August the surface current was northerly at 10-15 cm/sec. Surface winds were usually secondary to the distribution of mass as an influence on the surface circulation. Currents at 100 m were generally similar in direction to those at the surface, but the water moved more slowly. Between the surface and 100 m, southbound currents crossed the entrance of the Gulf at velocities of 5-10 cm/sec during January and April, forming frontal boundaries with the California Current water, which often occurred south of the entrance. From April to August, the median concentration of surface chlorophyll a increased from 0.65 to 0.97 mg/m3, while the median productivity increased from 5.6 mgC/m3/day in April to 17.8 mgC/m3/day in June before returning to 2.6 mgC/m3/day in August. Primary productivity was closely correlated with the concentration of surface chlorophyll a. Productivity was generally higher in the vicinity of the Gulf than that found for water in the open Pacific. Productivity was highest near Islas Las Tres Marias and second highest near Cabo San Lucas, both locations of local upwelling. The standing crop of phytoplankton was shown to be subjected to progressively heavier grazing pressure in the spring and summer by zooplankton. SPANISH: Un estudio de la distribución temporal y espacial de las larvas de atún y de las condiciones oceánicas concomitantes fue realizado en cooperación con la Dirección General de Pesca e Industrias Conexas de México. El trabajo experimental consistió en ocho cruceros hidrográficos realizados desde octubre 1966 hasta agosto 1967, cerca a la entrada del Golfo de California. De enero a abril, las corrientes superficiales fueron meridionales alcanzando velocidades hasta de 20 cm/seg; las corrientes en junio fueron variables en dirección y la mayoría con una velocidad de menos de 10 cm/seg; en agosto la corriente superficial fue septentrional a 10-15 cm/seg, Los vientos superficiales fueron por lo común secundarios a la dístríbucíón de la masa, como una influencia de la circulación superficial. Las corrientes a 100 m fueron generalmente similares en dirección a las de la superficie, pero el agua se movió más lentamente. Entre la superficie y los 100 m, las corrientes que se dirigen hacia el sur cruzaron la entrada del Golfo a velocidades de 5-10 cm/seg durante enero y abril formando límites frontales con el agua de la Corriente de California, que apareció a menudo al sur de la entrada. De abril a agosto, la concentración media de la clorofila a superficial aumentó de 0.65 a 0.97 mg/m3, mientras que la productividad mediana aumentó de 5.6 mgC/m3/día en abril hasta 17.8 mgC/m3/día en junio antes de regresar a 2.6 mgC/m3/día en agosto. La productividad primaria se correlacionó estrechamente con la concentración de clorofila a superficial. La productividad fue generalmente más alta en la vecindad del Golfo que aquella encontrada en el agua de alta mar del Pacífico. La productividad fue más alta cerca a las Islas Tres Marías, y el segundo máximo fue cerca al Cabo San Lucas, ambas localidades de afloramiento local. Se indicó que la reserva permanente de fitoplancton estaba sujeta por el zooplancton a una fuerta presión progresiva de apacentamiento en la primavera y el verano. (PDF contains 116 pages.)

Caractérisation des situations hydro-biologiques et potentialités de pêche thonière au Cap Lopez en Juin et Juillet 1972 et 1974

Surface temperature was measured by remote sensing through Cape Lopez (Gulf of Guinea) frontal region during the fishing season in June and July 1972 and 1974. Twelve typical situations are analysed through four main directions: surface situation, tendency, hydrobiological structure and availability to fisheries. The tuna behavior is analysed in relation with the frontal zone movements and a mechanism which tends to aggregate important shoals of tunas is presented.

Distribution, growth, and mortality of sailfish (Istiophorus platypterus) larvae in the northern Gulf of Mexico

Ichthyoplankton surveys were conducted in shelf and slope waters of the northern Gulf of Mexico during the months of May–September in 2005 and 2006 to investigate the potential role of this region as spawning and nursery habitat of sailfish (Istiophorus platypterus). During the two-year study, 2426 sailfish larvae were collected, ranging in size from 2.0 to 24.3 mm standard length. Mean density for all neuston net collections (n=288) combined was 1.5 sailfish per 1000 m2, and maximum density was observed within frontal features created by hydrodynamic convergence (2.3 sailfish per 1000 m2). Sagittal otoliths were extracted from 1330 larvae, and otolith microstructure analysis indicated that the sailfish ranged in age from 4 to 24 days after hatching (mean=10.5 d, standard deviation [SD]=3.2 d). Instantaneous growth coefficients (g) among survey periods (n=5) ranged from 0.113 to 0.127, and growth peaked during July 2005 collections when density within frontal features was highest. Daily instantaneous mortality rates (Z) ranged from 0.228 to 0.381, and Z was indexed to instantaneous weight-specific growth (G) to assess stage-specific production potential of larval cohorts. Ratios of G to Z were greater than 1.0 for all but one cohort examined, indicating that cohorts were gaining biomass during the majority of months investigated. Stage-specific production potential, in combination with catch rates and densities of larvae, indicates that the Gulf of Mexico likely represents important spawning and nursery habitat for sailfish.

Effect of diazinon 60 EC on Anabas testudineus, Channa punctatus and Barbodes gonionotus

Anabas testudineus, Channa punctatus and Barbodes gonionotus were exposed to 5.62, 6.25, 6.87, 7.50, 8.12 and 8.75 ppm; 1.13, 2.26, 3.39, 4.52, 5.65 and 6.78 ppm; and 2.00, 2.50, 3.00, 3.50, 4.00 and 4.50 ppm of Diazinon 60 EC, respectively. The median lethal concentration (LC50) values of Diazinon 60 EC on A. testudineus, C. punctatus and B. gonionotus were 6.55, 3.09 and 2.72 ppm for 96 hrs of exposure. The fish species showed several abnormal behaviors which included restlessness, arena movements, loss of equilibrium, increased opercular activities, strong spasm, paralysis and sudden quick movements during the exposure. For histopathological studies, A. testudineus, C. punctatus and B. gonionotus were exposed for 7 days to sublethal concentrations of 1.13 and 3.75 ppm; 1.13 and 2.26 ppm; and 1.13 and 2.26 ppm of Diazinon 60 EC, respectively. Hypertrophy, necrosis and pyknosis of hepatocytes, pyknosis and degenerative changes such as necrosis of tubular and haematopoietic cells of kidney were the major histopathological effects.

The early life history of swordfish (Xiphias gladius) in the western North Atlantic

Lengths and ages of sword-fish (Xiphias gladius) estimated from increments on otoliths of larvae collected in the Caribbean Sea, Florida Straits, and off the southeastern United States, indicated two growth phases. Larvae complete yolk and oil globule absorption 5 to 6 days after hatching (DAH). Larvae <13 mm preserved standard length (PSL) grow slowly (~0.3 mm/d); larvae from 13 to 115 mm PSL grow rapidly (~6 mm/d). The acceleration in growth rate at 13 days follows an abrupt (within 3 days) change in diet, and in jaw and alimentary canal structure. The diet of swordfish larvae is limited. Larvae <8 mm PSL from the Caribbean, Gulf of Mexico, and off the southeastern United States eat exclusively copepods, primarily of one genus, Corycaeus. Larvae 9 to 11 mm eat copepods and chaetognaths; larvae >11 mm eat exclusively neustonic fish larvae. This diet indicates that young larvae <11 mm occupy the near-surface pelagia, whereas, older and longer larvae are neustonic. Spawning dates for larvae collected in various regions of the western North Atlantic, along with the abundance and spatial distribution of the youngest larvae, indicate that spawning peaks in three seasons and in five regions. Swordfish spawn in the Caribbean Sea, or possibly to the east, in winter, and in the western Gulf of Mexico in spring. Elsewhere swordfish spawn year-round, but spawning peaks in the spring in the north-central Gulf of Mexico, in the summer off southern Florida, and in the spring and early summer off the southeastern United States. The western Gulf Stream frontal zone is the focus of spawning off the southeastern coast of the United States, whereas spawning in the Gulf of Mexico seems to be focused in the vicinity of the Gulf Loop Current. Larvae may use the Gulf of Mexico and the outer continental shelf off the east coast of the United States as nursery areas. Some larvae may be transported northward, but trans-Atlantic transport of larvae is unlikely.

Histopathological changes in gill, kidney and liver of an estuarine mullet, Liza parsia, induced by sublethal exposure to DDT

Liza parsia were exposed to sublethal (0.02 ppm) concentration of DDT for 15 days. The gill responded initially with copious secretion of mucus, oedematous separation of epithelial cells from the basement membrane and fusion of secondary gill lamellae. Hyperplasia of the cells lining primary gill lamellae and lamellar telangiectases (or aneurysms) was frequently seen after day 10 of exposure. Kidney exhibited hypertrophy of the epithelial cells lining proximal convoluted tubules which was followed by shrinkage in glomerular tufts, increase in Bowman's space, appearance of amorphous eosinophilic materials in the lumina of the tubules and focal necrosis on day 10 of the treatment. Hyaline droplets and casts were also encountered in the epithelial cells and lumina of the proximal tubules. Liver revealed an initial dilation of canaliculi and increased secretion of bile. Thereafter, the displacement of nuclei towards periphery of the hepatocytes, disorganization of blood sinusoids, pyknotic changes in nuclei, cytolysis and vacuolation as well as focal necrosis were noticed after day 10 of the intoxication.

Toxic effects of dimecron to Labeo rohita Ham. fingerlings during acute and chronic exposures: histopathological changes

The exposure to the highest dimecron cone. (8 mg/1) resulted in severe histopathological changes in different tissues of Labeo rohita fingerling. Cell necrosis, cytoplasmic vacuolation and pycnotic nuclei were major abnormalities observed in liver tissue. The degeneration of glomeruli and proximal tubules, cytoplasmic vacuolation and focal haemorrhagic area were noted in case of kidney tissues. Major changes observed in intestinal tissues were degeneration of villi, disintegrity of mucosal layers, necrosis of epithelial cells etc. However, hypertrophy of cells and granulation of cytoplasm were major histopathological changes observed in fish at lower dimecron cones. (4 mg/1).

Investigation of health status of juvenile exotic carps from various farming conditions of Bangladesh

Health status of juvenile silver carp, Hypophthalmichthys molitrix and silver barb, Barbodes gonionotus were investigated in three fish farms following different farming conditions through clinical and histopathological examinations for a period of nine months. Here the fishes and water quality parameters were sampled on monthly basis. Among the water quality parameters, water temperature has a distinct effect on fish health observed during the winter season. Different clinical signs like scale loss, dermal lesion, fin erosion were observed, while histopathologically necrosis, pyknosis, inflammation, haemorrhage, hypertrophy, vacuoles, missing of gill lamellae and clubbing were evidenced in the investigated fishes. The study showed that pathological symptoms were mainly increased during the winter season and H. molitrix exhibited severe pathological symptoms in compare to B. gonionotus during the investigation. It was also found that fishes of BAU farm was comparatively in the best condition, while, the fishes of other farms were severely affected during the experimental observations. In addition, disease like Epizootic Ulcerative Syndrome (EUS), protozoan disease and suspected bacterial colonies were clearly evidenced in the fishes of Government and NGO fish farms.

Dynamics of parasite population and its histopathological and histophysiological effects in the stomach of a freshwater fish

The caryophyllaeid cestode Lytocestoides fossilis infects the freshwater catfish Heteropneustes fossilis. The study was conducted for two consecutive years (2004-06) to record the bio-statistical data of the parasite. The incidence, intensity, density and index of infection of the parasite have been recorded. The infection was more during June to September, moderate during February to May and low during October to January. The parasite brought about severe histopathological changes in the stomach of infected fish. The changes observed in the stomach of fish included structural damage of the villi, inflammation, and fibrosis associated with hyperplasia and metaplasia. The hypertrophy of mucous layer led to vacuolation and necrosis. Histochemical changes were noticed with enhanced carbohydrate, protein and lipid contents. The enhanced substrate content in the infected organ might be due to the disfunctioning of the digestive tract, which results in the accumulation of various metabolites. Mucus secretion was triggered as a protective interaction against parasitic invasion. The parasitic infection affects the general metabolic state of the host and as the result, the fish becomes sluggish and moribund.

Health and disease status of Thai pangas, Pangasius hypophthalmus cultured in rural ponds of Mymensingh, Bangladesh

Thai pangas, Pangasius hypophthalmus is one of the important aquaculture species in Bangladesh. Over the last few years spectacular development has been taking place in Thai pangas farming in Mymensingh district. Due to availability of easy breeding and culture techniques as well as quick return, more and more people are converting their rice fields into pangas farms overnight. The present study was carried out to examine health and disease status of Thai pangas mainly through clinical, histopathological and bacteriological techniques. In addition, for collecting primary data on disease and health status of Thai pangas and the resultant socioeconomic impacts on rural households, questionnaire interview and participatory rural appraisal tools were used with selected farming households in three upazilas of Mymensingh district. The most prevalent diseases as reported by the farmers were red spot, followed by anal protrusion, tail and fin rot, pop eye, dropsy and gill rot. Other conditions like cotton wool type lesion, ulceration and white spot were reported but with lower incidence. Four isolates of Aeromonas hydrophila were recovered from kidney and lesion of diseased fish. Hemorrhage over the body especially near mouth and caudal region was noticed in the fishes associated with aeromonad infection. Internally, kidney, liver and spleen became swollen and enlarged. The isolates varied with their pathogenicity. All the four isolates were sensitive to Nitrofurantoin, Cotrimoxazole and Tetracycline but were resistant to Amoxycilline. An attempt was made to treat diseased fish with extracts from neem leaf, garlic and turmeric. Recovery of infection was monitored through mortality and histopathology. General histopathological changes of different organs were also studied. Extract from neem (Azadirachta indica) leaf gave better result. Telangiectasis, lamellar hypertrophy and hyperplasia hemorrhage, lamellar fusion, necrosis of lamellar epithelial cells, presence of parasites and their cysts were the major pathology of gills. Hemorrhagic lesion, pyknotic nuclei and melanomacrophage centers (MMC) were found in the liver of fish. Major pathologies in kidney of fish included presence of MMC, necrotic and ruptured kidney tubules, severe haemopoietic necrosis, and hemorrhage. The economic loss due to disease in Thai pangas farming was estimated from the difference between expected production and actual production. On an average, Thai pangas farmers of Mymensingh incur a loss of Tk. 23,104/ha/cycle due to fish disease (3.6% of expected total production). The loss, however, varied with location and size of farms, type of farmers and management practices. The study also highlighted fish health management related problems and recommended further work for the development of user-friendly farmer-oriented fish health management packages.

Structural features of geostrophic circulation in open region of the South China Sea

On the basis of observation data of water temperature and salinity the mean seasonal geostrophic circulation in open region of the South China Sea (SCS) was computed by the dynamic method relative to the 800 decibar reference surface. The results of computation let go to following notices: In both main monsoons (winter and summer) there are two main geostrophic eddies: the anticlockwise eddy in the northern and northwestern part, and the clockwise eddy in the southern part of the SCS with corresponding divergent and convergent zones. The main frontal zones go along the middle latitudes of the sea from the southern continental shelf of Vietnam to the area west of Luzon Island. The strength and stability of the current in winter are higher than in summer. The Kuroshio has an enough strong branch intruding into the SCS through Bashi Strait in winter creating in the sea the water structure similar to that of the Northwest Pacific subtropical and tropical regions. In summer the Kuroshio water can intrude directly only into the area southwest of Taiwan.