Factors influencing the timing and frequency of spawning and fecundity of the goldlined seabream (Rhabdosargus sarba) (Sparidae) in the lower reaches of an estuary

We have studied the reproductive biology of the goldlined seabream (Rhabdosargus sarba) in the lower Swan River Estuary in Western Australia, focusing particularly on elucidating the factors influencing the duration, timing, and frequency of spawning and on determining potential annual fecundity. Our results demonstrate that 1) Rhabdosargus sarba has indeterminate fecundity, 2) oocyte hydration commences soon after dusk (ca. 18:30 h) and is complete by ca. 01:30−04:30 h and 3) fish with ovaries containing migratory nucleus oocytes, hydrated oocytes, or postovulatory follicles were caught between July and November. However, in July and August, their prevalence was low, whereas that of fish with ovaries containing substantial numbers of atretic yolk granule oocytes was high. Thus, spawning activity did not start to peak until September (early spring), when salinities were rising markedly from their winter minima. The prevalence of spawning was positively correlated with tidal height and was greatest on days when the tide changed from flood to ebb at ca. 06:00 h, i.e., just after spawning had ceased. Because our estimate of the average daily prevalence of spawning by females during the spawning season (July to November) was 36.5%, individual females were estimated to spawn, on average, at intervals of about 2.7 days and thus about 45 times during that period. Therefore, because female R. sarba with total lengths of 180, 220, and 260 mm were estimated to have batch fecundities of about 4500, 7700, and 12,400 eggs, respectively, they had potential annual fecundities of about 204,300, 346,100 and 557,500 eggs, respectively. Because spawning occurs just prior to strong ebb tides, the eggs of R. sarba are likely to be transported out of the estuary into coastal waters where salinities remain at ca. 35‰. Such downstream transport would account for the fact that, although R. sarba exhibits substantial spawning activity in the lower Swan River Estuary, few of its early juveniles are recruited into the nearshore shallow waters of this estuary.

Tropical and subtropical moisture and southerly displaced North Pacific storm track: factors in the growth of late Quaternary lakes in the Mojave Desert

Historical flood events produced lakes in the Mojave River watershed in southeastern California and represent climatic conditions similar to those in the late Quaternary when perennial lakes formed in the Mojave Desert. Historical lakes are related to tropical and subtropical sources of moisture and an extreme southward shift of storm tracks. It is suggested that this atmospheric pattern occurred frequently during earlier periods with perennial lakes in the Mojave River drainage basin.

Influence of climate on environmental factors associated with long-term changes in chlorophyll production for the Sacramento-San Joaquin delta and Suisun Bay, California

Long-term changes in chlorophyll production were predicted from environmental variables for the Sacramento and San Joaquin rivers and Suisun Bay using Box-Jenkins transfer function models. Data used for the analyses were collected semimonthly or monthly between 1971 and 1987. Transfer function models developed to describe changes in chlorophyll production over time as a function of environmental variables were characterized by lagged responses and described between 39 and 51 percent of the data variation. Significant correlations between environmental variables and the California climate index (CA SLP) were used to develop a conceptual model of the link between regional climate and estuarine production.

Factors influencing colour production from the sugar medium used for the rapid approximation of bacterial counts in fishery products

Results of the studies carried out to elucidate the factors influencing colour production from the sugar medium used for the rapid approximation of bacterial counts in fishery products are reported. The effect of particle size, trace elements, salt soluble protein and non-protein fractions, rate of multiplication of bacteria, in the medium, surface bacteria and the rate of colour production by individual strains of bacteria were studied. It is observed that the best results are obtained when a sea-water homogenate is used.

Factors controlling drained weight in canned prawn

The paper gives an account of factors controlling the drained weight in canned prawn. The most important among them are concentration of brine used for blanching and blanching time which are found to be fixed and specific for different sizes of prawn irrespective of the quality of the material used. Other factors such as, acidity of brine used for filling the can, volume of brine, time of sterilization and time of cooling the blanched meat are also to some extent found responsible for fluctuations in drained weight.

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.

Factors controlling sterility in canned prawn

Probable sources of contamination of raw, blanched and processed meat at various stages of handling and methods for their rectification have been described in the paper. Inter-relationship between absolute sterility and commercial sterility with particular reference to the sanitation of the factory has been discussed.

Effect of some environmental factors on the acute toxicity of deltamethrin to common carp: a laboratory study under aerobic condition

The toxicity of xenobiotic in aquatic ecosystems is influenced by many factors such as ambient temperature, water hardness, pond soil type, etc. In the present study, it was observed that air temperature, water hardness and soil sediment have profound influence on the toxicity of deltamethrin to common carp fry (ay. length 3.5 ± 0.5 cm, ay. weight 0.58 ± 0.25 g); 96h LC(sub)50 values for common carp at 38.07 ± 2.20°C maximum and 27.86 ± 1.22°C minimum air temperature in soft and very hard water were 0.102 and 0.495 µg lˉ¹, respectively. This value had increased significantly to 2.37 and 3.02 µg at 30.55 ± 1.21°C maximum and 26.04 ± 0.61°C minimum air temperature, respectively. When sediment was included, 96h LC(sub)50 at 38.07°C maximum temperature in very hard water was 1.808 µg 1ˉ¹ and this had increased to 8.073 µg 1ˉ¹ when tested at 30.55°C maximum temperature. Due to the 7.5°C increase in maximum and 1.7°C in minimum temperature, toxicity increased significantly. Lower toxicity in very hard water in comparison to soft water may be due to the lower solubility of deltarnethrin and high level of calcium. Adsorption reaction of deltamethrin with clay, humus, FeOOH, MnOOH and particulate organic carbon, and complexation reaction with dissolved organic carbon were responsible for the lowered toxicity in the experiment with sediment. Exposure time had no significant effect on acute toxicity of deltamethrin.

Influence of some abiotic factors on the acute toxicity of cadmium to Cyprinus carpio

Hardness of water had significant effect on the acute toxicity of cadmium to common carp, Cyprinus carpio. The 96h LC sub(50) and safe application rate increased from 43.17 and 22.77 mg 1 super(-1) in soft water (0.9 mM Ca super(2+) l super(-1)) to 310.48 and 177.66 mg l super(-1), respectively, in very hard water (6.0 mM Ca super(2+) l super(-1)). In medium hard and hard water, 96h LC sub(50) values were 48.39 and 116.45 mg l super(-1). When sediments were included in the medium hard, hard and very hard water treatments, the 96h LC sub(50) were 111.20, 133.71 and 334.47 mg l super(-1), respectively. Among these values, the one for medium hard water with sediment treatment was significantly higher than medium hard water treatment; values for the other two treatments were non-significant when compared with respective water treatments. Sediment was able to reduce the acute toxicity of cadmium mainly due to the complexation of cadmium with dissolved organic carbon (DOC). At the lower hardness level, cadmium complexed with DOC and the acute toxicity was reduced significantly. At higher hardness, most of the DOC sites were occupied by calcium and the acute toxicity of cadmium was not significantly reduced in hard water with sediment and very hard water with sediment experiments in comparison to respective water treatments.

Hydrobiology of Colombo (Beira) Lake, 1. Diurnal variations in temperature, hydrochemical factors and zooplankton

An extensive study of the hydrobiology of the Colombo Lake was initiated by the authors in May 1969 as a contribution to the International Biological Program (Productivity of freshwater communities) by the Department of Zoology, Vidyalankara University of Ceylon, Kelaniya. The Colombo Lake often referred to as the Beira Lake covers an area of approximately 160 acres. The water is usually very turbid with a greenish blue appearance due to the presence of large quantities of blue green algae.

Characterization of the fisheries of the major and minor lakes of Uganda and the socio-economic factors influencing fishery exploitation

There is growing recognition that the performance of the fisheries sector depends on the communities responsible for activities within it. These communities include fishers, processors, fish mongers, traders, local leaders, fishery administrators etc. On the basis of this, characterisation and diagnostic studies were conducted in 1995 focussing on mainly the fishers and opinion leaders on the major and some minor water bodies in Uganda. The study revealed that the desire to earn income is the driving force behind the malfishing practices experienced on Uganda fisheries. The destructive fishing gears and fishing methods as responses advanced by the fishers and opinion leaders were seines and cast nets on lakes Victoria, Kyoga and Albert and to a less extent traps

The role of social,economic and cultural factors in the management of satellite lake fisheries in Uganda

The fisheries of small lakes are important for producing fish for local populations not clear the larger lakes.The satelite support important fisheries and other economic activities like fishing water for domestic purpose and tourism besides socio-cultural functions.

Studies on the fish ponds at Pitipana, Negombo 1: seasonal and diurnal variation of some hydrobiological factors

The present paper is a part of a detailed investigation on the biology of grey mullet, Mugli cephalus L., and the feasibility of its culture in the brackish waters of Sri Lanka. The authors present the results of investigation on the water quality of five experimental ponds at the Pitipana Brackishwater Fisheries Station, Negombo, carried out over a period of one year, December 1976 to November 1977, together with studies on the primary productivity are presented.