Environmental parameters and incidence of white spot disease in Penaeus monodon (Fab.) farming

An investigation was carried out to monitor management practices and to find out whether there is any relationship with occurrence of deadly white spot disease and environmental parameters. Three semi-intensive and a improved traditional shrimp farms were selected in which mass mortality of shrimp (Penaeus monodon) by white spot disease occurred previously. The farms were situated at two different geographical locations. Two ponds from each farm at random were selected for the study. Out of eight investigated ponds, 6 ponds in three farms were affected by the disease during investigation period. The non-affected ponds had relatively lower stocking density, lightly different management practice and were located at different geographical area. There was no significant variation in water quality parameters among the affected and non-affected ponds. No significant variations were recorded in pond preparation, source of Post Larvae (PL), water and feed management among the affected and non-affected ponds. The observation indicated that pond micro-organisms in a farm may not the only cause of the disease but some external factors also might be responsible for the outbreak of this disease.

Study of white spot disease in four native species in Persian Gulf by histopathology and PCR methods

After serious disease outbreak, caused by new virus (WSV), has been occurring among cultured penaeid shrimps in Asian countries like China since 1993 and then in Latin American countries, during June till July 2002 a rapid and high mortality in cultured Penaeus indicus in Abadan region located in south of Iran with typical signs and symptoms of White Spot Syndrome Virus was confirmed by different studies of Histopathology, PCR, TEM, Virology. This study was conducted for the purpose of determination of prevalence(rate of infection)/ROI and grading severity (SOI) of WSD to five species: 150 samples of captured shrimps and 90 samples of cultured ones; Penaeus indicus, P. semisulcatus, P. merguiensis, Parapenaopsis styliferus, and Metapenaeus affinis in 2005. 136 of 240 samples have shown clinical and macroscopical signs & symptoms including; white spots on carapase (0.5-2 mm), easily removing of cuticule, fragility of hepatopancreas and red color of motility limbs. Histopathological changes like specific intranuclear inclusion bodies (cowdry-type A) were observed in all target tissues (gill, epidermis, haemolymph and midgut) but not in hepatopancreas, among shrimps collected from various farms in the south and captured ones from Persian Gulf, even ones without clinical signs. ROI among species estimated, using the NATIVIDAD & LIGHTNER formula(1992b) and SOI were graded, using a generalized scheme for assigning a numerical qualitative value to severity grade of infection which was provided by LIGHTNER(1996), in consideration to histopathology and counting specific inclusion bodies in different stages(were modified by B. Gholamhoseini). Samples with clinical signs, showed grades more than 2. Most of the P. semisulcatus and M. affinis samples showed grade of 3, in the other hand in most of P. styliferus samples grade of 4 were observed, which can suggest different sensitivity of different species. All samples were tested by Nested PCR method with IQTm 2000 WSSV kit and 183 of 240 samples were positive and 3 1evel of infection which was shown in this PCR confirmed our SOI grades, but they were more specified.

Size-composition of Annual Landings in the White Shrimp, Litopenaeus setiferus, Fishery of the Northern Gulf of Mexico, 1960–2006: Its Trend and Relationships with Other Fishery-dependent Variable

The potential for growth overfishing in the white shrimp, Litopenaeus setiferus, fishery of the northern Gulf of Mexico appears to have been of limited concern to Federal or state shrimp management entities, following the cataclysmic drop in white shrimp abundance in the 1940’s. As expected from surplus production theory, a decrease in size of shrimp in the annual landings accompanies increasing fishing effort, and can eventually reduce the value of the landings. Growth overfishing can exacerbate such decline in value of the annual landings. We characterize trends in size-composition of annual landings and other annual fishery-dependent variables in this fishery to determine relationships between selected pairs of these variables and to determine whether growth overfishing occurred during 1960–2006. Signs of growth overfishing were equivocal. For example, as nominal fishing effort increased, the initially upward, decelerating trend in annual yield approached a local maximum in the 1980’s. However, an accelerating upward trend in yield followed as effort continued to increase. Yield then reached its highest point in the time series in 2006, as nominal fishing effort declined due to exogenous factors outside the control of shrimp fishery managers. The quadratic relationship between annual yield and nominal fishing effort exhibited a local maximum of 5.24(107) pounds (≈ MSY) at a nominal fishing effort level of 1.38(105) days fished. However, annual yield showed a continuous increase with decrease in size of shrimp in the landings. Annual inflation-adjusted ex-vessel value of the landings peaked in 1989, preceded by a peak in annual inflation-adjusted ex-vessel value per pound (i.e. price) in 1983. Changes in size composition of shrimp landings and their economic effects should be included among guidelines for future management of this white shrimp

Northerly Distribution of White Sharks, Carcharodon carcharias, in the Eastern Pacific and Relation to ENSO Events

Twenty-nine verified records of white sharks, Carcharodon carcharias, from British Columbia and Alaska waters (1961–2004) are presented. Record locations ranged from lat. 48°48ʹN to lat. 60°17ʹN, including the northernmost occurrence of a white shark and the first report of this species from the central Bering Sea. White sharks recorded from the study area were generally large, with 95% falling between 3.8 and 5.4 m in length. Mature white sharks of both sexes occur in British Columbia and Alaska waters, although they do not necessarily reproduce there. White sharks actively feed in the study area; their diet is similar to that reported for this species from Washington and northern California waters. Sea surface temperature (SST) concurrent with white shark records from the study area ranged from 16°C to between 6.4°C and 5.0°C, extending the lower extreme of the range of SST from which this species has been previously reported. White shark strandings are rarely reported, yet 16 (55%) of the records in this study are of beached animals; strandings generally occurred later in the year and at lower latitudes than nonstrandings. No significant correlation was found between white shark records in the study area and El Niño events and no records occurred during La Niña events. The data presented here indicate that white sharks are more abundant in the cold waters of British Columbia and Alaska than previous records suggest.

Effects of shear on eggs and larvae of striped bass, morone saxatilis, and white perch, M. americana

Shear stress, generated by water movement, can kill fish eggs and larvae by causing rotation or deformation. Through the use of an experimental apparatus, a series of shear (as dynes/cm2)-mortality equations for fixed time exposures were generated for striped bass and white perch eggs and larvae. Exposure of striped bass eggs to a shear level of 350 dynes/cm2 kills 36% of the eggs in 1 min; 69% in 2 min, and 88% in 4 min; exposure of larvae to 350 dynes/cm2 kills 9.3% in 1 min, 30.0% in 2 min, and 68.1% in 4 min. A shear level of 350 dynes/cm2 kills 38% of the white perch eggs in 1 min, 41% in 2 min, 89% in 5 min, 96% in 10 min, and 98% in 20 min. A shear level of 350 dynes/cm2 applied to white perch larvae destroys 38% of the larvae in 1 min, 52% in 2 min, and 75% in 4 min. Results are experimentally used in conjunction with the determination of shear levels in the Chesapeake and Delaware Canal and ship movement for the estimation of fish egg and larval mortalities in the field.

Das M74-Syndrom des Ostseelachses (Salmo salar): Symptome, Verbreitung und Ursachen

An overview is presented on the M74-Syndrome of Baltic salmon which is known since 1974 and which, since 1992, has caused considerable losses of artificially produced yolk-sac larvae in Swedish and Finnish hatcheries responsible for compensatory salmon stocking programmes. The syndrome only affects offspring of wild salmon ascending the rivers for spawning and not offspring derived from salmon broodstocks permanently kept in hatcheries. The syndrome seems to be restricted to the Baltic Sea where it has been recorded in all of the remaining Swedish (except the west coast) and Finnish salmon rivers as well as in populations of Estonian rivers and the Russian River Neva. In Sweden and in Finland, the syndrome has been recorded in recent years in offspring of up to 80 % of female salmon used for spawning and resulted in a larval mortality of up to 90 %. A nutrition-associated thiamine (vitamin B1) deficiency is considered as primary cause. However, other environmental factors seem to be involved in addition. There is concern that the syndrome constitutes a major threat with respect to the survival of the few still naturally reproducing populations of Baltic salmon.

The diatoms of Longans lake-vegetation. Fossil diatom flora. [Translation from: Acta Phytogeographica Suecica 36 73-86, 1955. ]

Sediment samples were taken from Lake Langans in Sweden and fossilised diatoms analysed. Sample methods and environmental factors are discussed. Species with a characteristic occurrence are described. The article discusses diatom-thanatocoenoses as indicators of environment.