Underwater warp tension meter

A self-contained electronic solid-state instrument capable of measuring the tension between the different parts of a trawl net in operation, has been designed and developed for the measurement in the range 0 to 300 kg with an accuracy of ± 2 kg. The instrument is useful for measuring the resistance to motion of various accessories of a trawl net. It consists of an inductive type underwater tension transducer and an electronic indicating meter kept on board the vessel, both the units being connected by electric cable.

A preliminary survey of the helminth fish parasites in Imo River

A preliminary survey of the helminth fish parasites was carried out in Imo River (Nigeria). A total of 191 fishes belonging to 15 genera were examined and only 13.6% were infested with various species of helminth parasites which is low percentage of infection. The following helminth parasites were recorded. Wenyonia virilis, kainji; Wenyonia sp., Procamallanus laeviconchus; Procamallanus sp., Sprionoura congolense; Spironoura sp., Cucullanus sp. and Serradacnitis serrata. It was found that helminth parasites showed some degree of specificity in their distribution within their fish hosts. This specificity could be as a result of the physiochemical and physiological factors operating in the gut such as pH, osmotic tension, oxygen tension and nutrient levels. The results also revealed that age and sex influence helminth parasites infections in fishes

Physiological ecology of the ciliated protozoon Loxodes

Loxodes faces special problems in living close to the oxic-anoxic boundary. In tightly-stratified ponds like Priest Pot its optimum environment may be quite narrow and it can be displaced by the slightest turbulence. Loxodes cannot sense an O sub(2) gradient directly but its ability to perceive gravity allows it to make relatively long vertical migrations. It is also sensitive to light and oxygen and it uses these environmental cues to modulate the parameters of its random motility: in the dark, it aggregates at a low O sub(2) tension and in bright light it aggregates in anoxic water. The oxic-anoxic boundary is also a zone where O sub(2) may be a scarce and transient resource, but Loxodes) can switch to nitrate respiration and exploit the pool of nitrate that often exists close to the base of the oxycline.

The effect of autotrawl systems on the performance of a survey trawl

Three aspects of a survey bottom trawl performance—1) trawl geometry (i.e., net spread, door spread, and headrope height); 2) footrope distance off-bottom; and 3) bridle distance off-bottom—were compared among hauls by using either of two autotrawl systems (equal tension and net symmetry) and hauls conducted with towing cables of equal length and locked winches. The effects of environmental conditions, vessel heave, crabbing (i.e., the difference between vessel heading and actual vessel course over ground), and bottom current on trawl performance with three trawling modes were investigated. Means and standard deviations of trawl geometry measures were not significantly different between autotrawl and locked-winch systems. Bottom trawls performed better with either autotrawl system as compared to trawling with locked winches by reducing the variance and increasing the symmetry of the footrope contact with the bottom. The equal tension autotrawl system was most effective in counteracting effects of environmental conditions on footrope bottom contact. Footrope bottom contact was most inf luenced by environmental conditions during tows with locked winches. Both of the autotrawl systems also reduced the variance and increased the symmetry of bridle bottom contact. Autotrawl systems proved to be effective in decreasing the effects of environmental factors on some aspects of trawl performance and, as a result, have the potential to reduce among-haul variance in catchability of survey trawls. Therefore, by incorporating an autotrawl system into standard survey procedures, precision of survey estimates of relative abundance

On the relative efficiency of different shaped otter boards

Rectangular, horizontal curved and oval otter boards were tested under identical fishing conditions and their relative efficiency ascertained on the basis of towing tension and the horizontal opening of the boards. While the tension in the warps with the different otter boards was not significant, the horizontal curved board gave increased lateral spread to the net.

On the relative utility of different methods to increase the vertical height in an otter trawl

Comparative fishing experiments to study the relative utility of different methods for increased vertical spread of bottom trawl and the availability of off bottom fishes in the region were made using gussets, kite, separate float line and side panels on a two seam net. The catch rates as well as composition of fish were studied. The opening of the trawl mouth, both horizontally and vertically, under different operating gears and towing tension on warps were measured and estimated for comparison purposes. Better catch rate with good quality fishes was obtained with the gear operated with separate float line. With kite, the vertical spread was increased with less catch indicating poor concentration of off bottom fishes.

Development of trawls for medium sized trawlers for Veraval, north-west coast of India

Comparative fishing experiments with 25 m bulged belly and 25 m six seam trawls were carried out to study the relative efficiency of the gear. Bulged belly trawl was found more efficient than the other at depths below 40 m. The tension and horizontal opening were more in bulged belly and six seam trawl respectively. Bulged belly caught more of prawns and lobsters but there was no significant difference in the catch of sciaenids, cephalopods and ribbon fishes in the two nets.

On the comparative fishing experiments with a four-seam and a two-seam trawls on the east coast

Fishing experiments were undertaken to study the relative utility of a newly designed four seam type net on a conventional two seam net at the centre along the East Coast in both inshore and deeper zones (up to 100m.) and the results indicated that the new four seam net has given higher catch rate of 6 to 8% more with higher catch rate of fish supposed to belong to off bottom region. Further this gear found more selective in obtaining Lactarius, which is one of the good variety of fish from trawlers, in both quantity as well as in quality. In terms of horizontal spread this new net gave less on comparison with the conventional two seam net, thereby showed corresponding increase in vertical spread; but warp tension remained more or less same in both the gear. Both gear have worked equally well in majority of depth ranges experimented with optimum spread. Finally the results indicated that the new net can work well from the present trawlers along the coast.

Some physical properties of the muscle lipid of two freshwater teleosts, Ophicephalus striatus (Bloch.) and Clarias batrachus (Linn.)

Various physical properties (viscosity, fluidity, surface tension and specific gravity) have been determined for muscle lipids of Ophicephalus striatus and Clarias batrachus. Results are presented and the methods used in determination noted. The physical parameters studied are found to be species-specific.

Some changes in the physical qualities of muscle lipid of the freshwater murrel, Ophicephalus striatus (bloch.) during storage

The present communication reports the changes in the specific gravity, coefficient of viscosity, fluidity and surface tension of the muscle lipid of O. striatus, a common freshwater murrel, when stored at room temp (32 ± 2°C) The specific gravity of muscle lipid was found to rise from 0.894 to 0.912 during the first 25 days of storage but registered the highest (0.925) when stored for 50 days. Surface tension seemed to rise with the duration of storage. This was, presumably, due to an increase in the forces with which the molecules in the surface of the lipid tended to compress the molecules below to the smallest possible volume. During the period of storage marked changes seemed to occur in the direction of an increase in the value of the coefficient of viscosity and a reciprocal decline in the fluidity. Evidently, the observed increase in the viscosity seemed to be the result of increased internal friction between different molecular layers of the lipid, whereas a decline in the fluidity was perhaps the consequence of its inverse correlation with the coefficient of viscosity.

On the comparative efficiency of "V" shaped and rectangular flat otter boards for trawling off Veraval, north west coast of India

V shaped all steel boards, with their inherent stability to tide over obstacles and mud, interchangeability of starboard and portside boards are found to be superior to conventional flat rectangular boards for bottom trawling. These are cheaper in construction, offer less resistance and give longer service. Comparative trials with the two types of boards showed significant difference in tension between the boards but not in catch or horizontal opening.

Organic pollution in culture water resulting from excess feed and metabolite buildup

Penaeus monodon postlarvae were subjected to increasing feed concentrations and their growth and survival rates were recorded. Measurements were made of dissolved organic matter, and ammonia and nitrite-nitrogen concentrations. Survival was highest at the lowest feeding level and decreased as feed concentration increased. It is concluded that although organic matter enriches the food supply for P. monodon postlarvae, at higher concentration levels it can pollute the culture water, which in turn leads to mass mortality of the postlarvae. Secondly, the survival rate of P. monodon postlarvae is directly related to dissolved organic matter concentration, oxygen tension, and ammonia-nitrogen concentrations in the culture water. Even at sublethal levels these adverse environmental conditions decrease the survival rate.