Population dynamics of the ribbon fish, Lepturacanthus savala (Cuvier 1829) from the north-eastern part of the Bay of Bengal

Population parameters of Lepturacanthus savala from the trawl catches in the north-eastern part of the Bay of Bengal, Bangladesh were investigated based on length frequency data, using complete ELEFAN computer program. The asymptotic length (Lα) and growth constant (K) were estimated to be 106.50 cm (total length) and 0.80/year respectively. Based on these growth parameters, the total mortality (Z) was estimated to be 1.89. The estimated values for natural mortality (M) and fishing mortality (F) were 1.08 and 0.81 respectively. The estimated value for the exploitation rate (E) using the length converted catch curve was 0.43. The recruitment pattern showed two peaks per year. The estimated sizes of L. savala at 25, 50 and 75% probabilities of capture were 57.49, 60.39 and 63.28 cm respectively. The estimated length weight relationship for combined sex was W=0.00093 TL(super)2.97

A 30-Year History of Tide and Current Measurements in Elkhorn Slough, California

Elkhorn Slough was first exposed to direct tidal forcing from the waters of Monterey Bay with the construction of Moss Landing Harbor in 1946. Elkhorn Slough is located mid-way between Santa Cruz and Monterey close to the head of Monterey Submarine Canyon. It follows a 10 km circuitous path inland from its entrance at Moss Landing Harbor. Today, Elkhorn Slough is a habitat and sanctuary for a wide variety of marine mammals, fish, and seabirds. The Slough also serves as a sink and pathway for various nutrients and pollutants. These attributes are directly or indirectly affected by its circulation and physical properties. Currents, tides and physical properties of Elkhorn Slough have been observed on an irregular basis since 1970. Based on these observations, the physical characteristics of Elkhorn Slough are examined and summarized. Elkhorn Slough is an ebb-dominated estuary and, as a result, the rise and fall of the tides is asymmetric. The fact that lower low water always follows higher high water and the tidal asymmetry produces ebb currents that are stronger than flooding currents. The presence of extensive mud flats and Salicornia marsh contribute to tidal distortion. Tidal distortion also produces several shallow water constituents including the M3, M4, and M6 overtides and the 2MK3 and MK3 compound tides. Tidal elevations and currents are approximately in quadrature; thus, the tides in Elkhorn Slough have some of the characters of a standing wave system. The temperature and salinity of lower Elkhorn Slough waters reflect, to a large extent, the influence of Monterey Bay waters, whereas the temperature and salinity of the waters of the upper Slough (>5 km from the mouth) are more sensitive to local processes. During the summer, temperature and salinity are higher in the upper slough due to local heating and evaporation. Maximum tidal currents in Elkhorn Slough have increased from approximately 75 to 120 cm/s over the past 30 years. This increase in current speed is primarily due to the change in tidal prism which has increased from approximately 2.5 to 6.2 x 106 m3 between 1956 and 1993. The increase in tidal prism is the result of both 3 rapid man-made changes to the Slough, and the continuing process of tidal erosion. Because of the increase in the tidal prism, the currents in Elkhorn Slough exhibit positive feedback, a process with uncertain consequences. [PDF contains 55 pages]

A study of flow conditions near the substratum in an experimental channel [Translation from: Verhandlungen der Internationalen Vereinigung fur Theoretische und Angewandte Limnologie 18, 718-725, 1972]

In a slow flow, on a smooth uniform substratum, a limited bed allows the existence of currents slow enough for benthic invertebrates. These conditions rarely occur naturally. The investigations carried out in this work aimed, on an intermediary scale, to define the influence of irregularities in the substratum on flow near the bottom. The substrata used were made of glass marbles. The investigations were carried out in a transparent channel of 70 cm in length and a rectangular section 10 x 5 cm. The data was analysed to study the general evolution of flow in terms of average speeds and the appearance of the turbulence near the bottom.

Colpodella pugnax Cienk., Protomonas amyli Cienk., Protomonas spirogyrae Borzi and Protomonas huxleyi Haeckel [Translation from: Die Pilzthiere oder Schleimpilze (ed. W. Zopf), pp. 115-124. Breslau, Eduard Trewendt, 1885]

Morphological observations are given for Colpodella pugnax Cienk., Protomonas amyli Cienk., Protomonas spirogyrae Borzi and Protomonas huxleyi Haeckel.

The significance of sedimentation and sediments to phytoplankton growth in drinking-water reservoirs

In the mesotrophic-eutrophic Saidenbach Reservoir in Saxony, the nanoplankton and cyanobacteria have increased at the expense of diatom dominance, due to a doubling of the external phosphorus load in the last 15 years. However, the phosphorus sedimentation flux is still very high (up to 80% of the input), corresponding to more than 2 g m2 d-1 in terms of dry weight. There is a strong correlation between the abundance of diatoms in the euphotic zone and their sedimentation flux (with a delay of about 2 weeks). Only about 25% of the deposited material could be clearly attributed to plankton biomass; the remainder resulted from flocculation and precipitation processes or directly from the inflow of clay minerals. The ash content of the deposited material was high (73%). Thus the sedimentation flux can be considered to operate as an internal water-treatment/oligotrophication process within the lake. The neighbouring Neunzehnhain Reservoir still has a very clear water with a transparency up to 18 m depth. Though the sediment was not much lower than Saidenbach sediment in total phosphorus and total numbers of bacteria, sulphide was always absent and the ratio of Fe 2+ to Fe 3+ was very low in the upper (0- 5 cm) layer. Thus the external and internal phosphorus loads do not attain the critical level necessary to induce a ”phosphorus - phytoplankton” feedback loop.

Age and growth of spiny dogfish (Squalus acanthias) in the Gulf of Alaska: analysis of alternative growth models

Ten growth models were fitted to age and growth data for spiny dogfish (Squalus acanthias) in the Gulf of Alaska. Previous studies of spiny dogfish growth have all fitted the t0 formulation of the von Bertalanffy model without examination of alternative models. Among the alternatives, we present a new two-phase von Bertalanffy growth model formulation with a logistically scaled k parameter and which estimates L0. A total of 1602 dogfish were aged from opportunistic collections with longline, rod and reel, set net, and trawling gear in the eastern and central Gulf of Alaska between 2004 and 2007. Ages were estimated from the median band count of three independent readings of the second dorsal spine plus the estimated number of worn bands for worn spines. Owing to a lack of small dogfish in the samples, lengths at age of small individuals were back-calculated from a subsample of 153 dogfish with unworn spines. The von Bertalanffy, two-parameter von Bertalanffy, two-phase von Bertalanffy, Gompertz, two-parameter Gompertz, and logistic models were fitted to length-at-age data for each sex separately, both with and without back-calculated lengths at age. The two-phase von Bertalanffy growth model produced the statistically best fit for both sexes of Gulf of Alaska spiny dogfish, resulting in L∞ = 87.2 and 102.5 cm and k= 0.106 and 0.058 for males and females, respectively.

Studies on some physico-chemical factors of Kaptai lake

The present investigation dealt with the climatic and some physico-chemical conditions of the Kaptai lake with respect to their monthly variation. Air temperature was found always higher than water temperature. Vertical variation in temperature (0.8-4.7°C) was observed in all months. The water level fluctuates appreciably throughout the year. Wide seasonal fluctuations were also noted in water transparency. The lake was found to be slightly hard and alkaline pH. Dissolved oxygen (DO) (6.4-9.1 mg/l) and free carbondioxide (4.7- 6.0 mg/l) contents showed favourable condition for aquatic lives. DO at different depth has shown no wide variation (1.0-2.4 mg/1). Conductivity ranged between 91.9±7.1 and 106.4 ±5.2 mS/cm.

Length-weight relationship and condition factor of black carp (Mylopharyngodon spiceus Richardson) in Bangladesh

The length-weight relationship and condition factor of Mylopharyngodon spiceus were determined. The result of the study showed the dependence of weight (W) on the total length (L) in the following form: W= 0.006L(super 3.156) or in the logarithmic form Log W=- 2.1851 + 3.156 Log L. Standard errors of length and weight were 0.674 cm and 3.214 g respectively. The co-efficient correlation "r" was found to be 0.972 which indicated that the relationship between length and body weight of the fish was highly significant. The t-test also indicated that the correlation between length and weight was significant. The range and mean value of condition factor (K) were 0.865 to 1.041 and 0.958 respectively.

Stock dynamics of horse mackerel, megalaspis cordyla (Linnaeus) along northwest coast of India

The stock dynamics of horse mackerel, Megalaspis cordyla, along the northwest coast of India has been studied using length frequency data recorded from commercial landings and trawl catches of research-cum-training vessel M.F.V. Saraswati. The growth parameters for this species has been estimated to be L∞=54 cm and K=0.49 per annum. The natural and fishing mortality for the stock have been worked out to be 0.93 and 0.91 per annum respectively. The study indicated that the stock is fished at a safer fishing mortality level F sub(0.1), lower than F sub(msy) level.

Growth performance, recovery rate and fish yield of GIFT strain at various water depths under rice-fish culture systems

Effect of water depth on recovery rate, growth performance and fish yield of GIFT in the rice-fish production systems was studies in experimental plots of 123 m2 with a pond refuge of I meter deep which covered 10% of the total land area. Mortality rate of fish was very low ranging from 0.81-1.63%. However, at harvest, recovery rate ranged from 76.69-82.93% with the highest recovery at 11-15 em of water depth. Significantly the highest absolute growth (99.97) and specific growth rate (2.42%) were found at 21-25 cm water depth. The same treatment also produced significantly higher fish yield (909.76 kg/ha) although statistically similar to the fish yield (862.60 kg/ha) obtained at ll-15 em of water depth. Results also suggested that higher water depth can produce bigger fish but no significant effects of water depth was found on fish yield in the treatments 11-15 cm and 21-25 cm water depths of this experiment.

Check list of plankton of the northern Red Sea

Qualitative estimation of phytoplankton and zooplankton of the northern Red Sea and Gulf of Aqaba were carried out from four sites: Sharm El-Sheikh, Taba, Hurghada and Safaga. A total of 106 species and varieties of phytoplankton were identified including 41 diatoms, 53 dinoflagellates, 10 cyanophytes and 2 chlorophytes. The highest number of species was recorded at Sharm El-Sheikh (46 spp), followed by Safaga (40 spp), Taba (30 spp), and Hurghada (23 spp). About 95 of the recorded species were previously mentioned by different authors in the Red Sea and Gulf of Suez. Eleven species are considered new to the Red Sea. About 115 species of zooplankton were recorded from the different sites. They were dominated by four main phyla namely: Arthropoda, Protozoa, Mollusca, and Urochordata. Sharm El-Sheikh contributed the highest number of species (91) followed by Safaga (47) and Taba (34). Hurghada contributed the least (26). Copepoda dominated the other groups at the four sites. The appearances of Spirulina platensis, Pediastrum simplex, and Oscillatoria spp. of phytoplankton in addition to the rotifer species and the protozoan Difflugia oblongata of zooplankton impart a characteristic feature of inland freshwater discharge due to wastewater dumping at sea in these regions resulting from the expansion of cities and hotels along the coast.

Growth rates of Tilapia esculenta (Graham) and Tilapia zillii (Gervais) under cultivation in ponds at Nyegezi, Tanzania

Aquaculture in Tanzania is still on a subsistence level and most of the ponds are maintained as part time job. The ponds are too small, shallow and over crowded with stunted Tilapia spp. In the present paper the results of experiments conducted in ponds at Nyegezi with T. esculenta and T. zillii are presented. This was part of an overall project of developing techniques of fish cultures with Tilapia under the limited existing conditions at Nyegezi. In a mono - species culture experiement with Tilapia zillii in nine month's time an average size of 172.8 mm/115.0 g was attained. In another experiment with T. zillii and T. esculenta in thirteen month's time, T. zillii attained an average size of 180.2mm/106.6 g and T. esculenta 193.6 mm/118.8 g. In another experiment with intensive feeding schedule an average size of 179.3 mm/126.6 g was attained by T. zillii and 191.0 mm/125.0 g by T. esculenta in four month's time. A locally prepared supplimentary feed with local Brewery Waste and Fish Meal (10:1) was readily accepted by both species of Tilapia. T. zillii voraciously fed on Cabbage leaves, Cauliflower leaves, Chinese cabbage leaves, Cassava leaves and on the common weed Comalina sp. Though all the items mentioned above were readily accepted by T. zillii feeding with Comaltna sp. was the easiest and most convenient because of its availability. In an intensive feeding experiment with vegetable leaves/Comalina sp. and the locally prepared supplimentary feed the fishes attained table size in four months time. Cement cistens of 5 X 3 X 1½ m size could be conveniently used for breeding both species of Tilapia. T. zillii had semi adhesive eggs and they were deposited on the sides of the cement wall. The number of young ones in a brood ranged from 160 to 314 in T. esculenta and 687 to 4,356 in T. zillii.