Some aspects of reproductive biology of two sciaenids, Otolithes cuvieri Trewavas and Johnius elongatus Mohan: maturation, spawning, sex ratio and fecundity

The gonads of Otolithes cuvieri and Johnius elongatus are described in seven maturity stages. O. Cuvieri spawns once a year from April to September as evidence by ova diameter frequency distribution and GSI values. 50% maturity is attained at 210mm TL in males and 200mm TL in females. Fecundity ranged from 2387 to 104379 with a mean value of 33502. Log-Log relationship between fecundity and total lenght, body weight and ovary weight were determined. An overall sex ratio of 1.54:1.00 was unequal in favour of males. Johnius elongatus spawns twice a year from January-February to Aprile-May and from August to October as evidence by ova diameter frequency distribution and GSI values. 50% maturity is attained at 140-143mm TL in both sexes. Fecundity ranged from 4238 to 167669 with a mean value of 42818. Log-Log relationship between fecundity and total lenght, body weign and ovary weight were determined. An overall sex ratio of 1.00:1.20 was unequal in favour of females.

Fecundity of the sole Euryglossa orientalis (Bl. & Schn.)(family: Soleidae) from Karachi coast

During the present study fecundity of 30 ovaries of Euryglossa orientalis was determined. Fecundity ranged from 9922 to 8389 with a mean value of 36361. The number of ova in the dorsal lobe was less than that of ventral lobe. Log-log relationship between fecundity and total length, fish weight, ovary weight and ovary length were determined.

A few observations on the biology of Tachysurus thalassinus Ruppell from Veraval (Gujarat)

The length-weight relationship of T. thalassinus differed in the sexes and, therefore separate equations were obtained; for males log W = -5.1728 4- 3.0495 log L; and for females log W = -5.7456 + 3.2798 log L. The spawning period of this species appears to be restricted to a short period from October to November. Fecundity has been found to range from 33 to 55 mature eggs in specimens of the size range 421-564mm. The sex ratio of males to females was 1.8:1. T. thalassinus is a bottom carnivore, crustaceans ranking first in food followed by fishes, mollusc and polychaetes.

Field trials on culture of Clarias batrachus

Culture of Magur, Clarias batrachus on an experimental basis was carried out for a total of 159 days in 6 earthen ponds each of 0.02 ha in area, singly in 2 ponds and in combination with Rohu, Labeo rohita in 4 ponds. Three different artificial feeds were used. Growth of Magur varied from 89 to 110 and survival form 93 to 100%. Out of the 3 feeds used, feed formulation 2 yielded better results. Length-weight relationship parameters were found as log W=0.4979067+1.878346 log L; -1.1116438+2.3511497 log L; and -1.238157+2.433125 log L indicating growth to be not isometric. Relative condition factor (K u) was close to or higher than 1.0 only in fishes higher than 200 mm of total length; K. values which were less than 1.0 up to January, reached values greater than 1.0 by March-April. Condition appears to be influenced by spawning rather than feeding.

Disinfection of aquarium effluents by chlorination and UV treatment

The study was conducted to investigate the efficacy of chlorine and UV irradiation in disinfecting aquarium effluent. A non-agglutinating, a virulent strain of Aeromonas salmonicida (NCIMB 11 02) was used as the test organism. Effluents from a fish tank were inoculated with a suspension of test organisms and subsequently treated with different concentrations of hypochlorite and UV irradiation separately and simultaneously. When used alone, 1.0 ppm hypochlorite reduced the viable cell count from 6.5 log to 3.0 log within 20 minutes of contact period. On the other hand, when used in combination with UV irradiation only 0.5 ppm hypochlorite exerted the same bactericidal effect within the same contact period as was observed with 1.0 ppm hypochlorite alone. This result indicated that required dose of disinfectant for the disinfection of aquarium effluents can be considerably reduced when it is used in combination with UV irradiation.

Studies on growth and mortality of Cyprinus carpio (Lin.) in floating ponds

Growth and mortality rate of Cyprinus carpio (Linnaeus) under five different dietary conditions were studied in fifteen floating net cages in ponds of the Bangladesh Agricultural University Campus, Mymensingh. Growth rate was found to vary under different dietary conditions. The feed with mixture of 25% rice bran, 5% wheat bran, 30% linseed oil cake and 40% water hyacinth leaf meal exhibited the highest growth rate. The gain of log of body weight per unit increase of log of total length was significant. Significant survivals of the fishes were found.

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.

Yielding of engineering polymers at strain rates of up to 500 s-1

A method is described for measuring the mechanical properties of polymers in compression at strain rates in the range approximately 300-500 s-1. A gravity-driven pendulum is used to load a specimen on the end of an instrumented Hopkinson output bar and the results are processed by a microcomputer. Stress-strain curves up to high strains are presented for polycarbonate, polyethersulphone and high density polyethylene over a range of temperatures. The value of yield stress, for all three polymers, was found to vary linearly with log (strain rate) at strain rates up to 500 s-1. © 1985.

Some aspects of the biology of Otolithes cuvieri (Trewavas) and Johnius glaucus (Day) from Veraval

The length-weight relationship in O. cuvieri and J. glaucus can be described by the equations log W=-5.27997+3.13225 log L and log W=-4.93431+3.02556 log L respectively. The length at first maturity in O. cuvieri is estimated as 256 mm and in J. glaucus as 180 mm. Empty stomachs occurred in high percentage in both the species. A study on composition of food items revealed that O. cuvieri feeds on a variety of organisms while J. glaucus a selective feeder.

Length-weight relationship in the Asian seabass, Lates calcarifer (Bloch) under culture condition

Asian seabass, Lates calcarifer (Bloch) - a catadromous centropomid perch, is a good candidate species for brackishwater aquaculture in India. The length-weight relationship and the relative condition of L. calcarifer were assessed under culture condition. The length of the fish samples ranged from 25 to 240 mm and the relative condition (w sub(r)) of the fish for different length groups ranged from 99.54 to 104.39, indicating the good condition of the fish. The regression analysis of log-transformed length-weight data was carried out and the 'b' coefficient indicates the good condition of fish showing an isometric growth in the juvenile phase under culture condition.

On the biology of Tachysurus caelatus (Valenciennes) from Veraval

The length-weight relationship of males and females of Tachysurus caelatus can be described by the equation log W = -5.6659 + 3.2685 log L and log W = -4.7648 + 2.9104 log L, respectively. A sex ratio of 1.37 males : 1.00 females was observed. Fecundity in the fish measuring 385 to 402 mm ranges between 44 and 55 ova. It is a demersal carnivorous feeder, feeding chiefly on crustaceans, fish, molluscs and polychaetes.

Growth of the buccaneer anchovy Encrasicholina punctifer off Mozambique, based on samples collected in research surveys

Growth of Encrasicholina punctifer (Engraulididae) is estimated, based on samples obtained during five surveys on Sofala Bank (central Mozambique). The estimated values of the von Bertalanffy growth function, TL∞=12 cm and K=2.0 yearˉ¹ are compared with results of growth studies elsewhere in the Indo-Pacific region, based mainly on the index Φ=log(sub)10 K+2*log(sub)10L∞ assumed to be constant within species. This comparison is rendered difficult by the uncertain taxonomical status of stolephorid anchovies.

Monitoring of the socio-economics status of fisher communties on Lake Victoria, Uganda

The objectives of the study was to provide information on the changes in the socio- economis status of the fisher communities.The study aimed at contributing to the following selected OVIs of the IFMP log frame:"10% increased in incomes from fish catches by fishing crews by EOP",20% women in BMUs reporting increased household incomefrom fishing by EOP","50% women and fishing crews in BMUs reporting greater say in fisheries decision making.

Estimations of maximum sustainable fish yields and stocking densities of inland reservoirs of Sri Lanka

The Maximum Sustainable Yields of all fish species for 9 man-made reservoirs in Sri Lanka were calculated by the simplified version of Schaefer Model. The relationship between the Maximum Sustainable Yield (MSY) and Morpho-edaphic Index, (MEI) for Sri Lankan reservoirs was found to be: Log sub(e) MSY = 0.9005 log sub(e) MEI + 1.9220. MSY for these reservoirs were estimated using this relationship. The number of Tilapia) juveniles needed to be recruited to the fisheries of some reservoirs in addition to the present recruitment to increase the fish production to the level estimated by MEI relationship were calculated mathematically.

Relationship between total length and mouth gap of some commercially important carp fry

The estimated regression equation for total length and mouth gape computed were Log TL = Log 0.23 + 0.663 log MG (vertically) (r = 0.960) and Log TL = Log 0.08 + 0.686 log MG (horizontally) (r = 0.949). In case of rohu average total length from 11350 mm to 23775 mm and mouth gape 805 um to 1225 um (vertically) and 700 um to 1110 um (horizontally) between the first day of mouth opening up to 15 days. The regression equation for total length and mouth gap were Log TL = Log 0.20 + 0.660 log MG (vertically) (r = 0.935) and Log TL = Log 0.02 + 0698 log MG (horizontally) ( r = 0.907). In case of silver carp average total length from 12800 ,urn to 33555 um and mouth gape 690 um to 1210 um (vertically) and 615 um to 1115 um (horizontally) between the first day of mouth opening up to 15 days. The regression equation for total length and mouth gape were Log TL = Log 0.36 + 0.596 log MG (vertically) (r = 0.936) and Log TL = Log 0.26 + 0.607 log MG (horizontally) (r = 0.891). The relationship between total length and mouth gape (vertically and horizontally) of the studied fry were found to be linear and highly significant.