Predatory behaviour of a snakehead fish (Channa striatus Bloch)

The predatory behaviour of a snake-head, Channa striatus (Bloch) on Labeo rohita fingerlings was studied in the laboratory. The study was conducted with six C. striatus (120 to 210 g and 22 to 28 cm) over 24h a day for 3 weeks. Three different sizes prey of large (2.00g and 5.8cm), medium (1.30g and 4.5cm) and small (0.72g and 3.5cm) were used for the first week and then medium size prey for 2nd and 3rd weeks. All the predators preferred eating the small group of L. rohita although all three size groups of L. rohita offered were available. It was found that the prey fishes remained together aside of the aquarium from the predator. Predator first targeted a prey, drove fast towards it, the prey tried to escape from the predator's attack using a specific route and finally the predator grasped the prey on head first and then engulfed. The handling time ranged between 45 and 50 sec. The time of peak feeding was found in the morning and in the evening of day. When 2 or 3 predators were kept in one aquarium, they engaged in fighting, head on, followed by an attack on the mouth region by the dominant one, and subsequently on the pectoral fin and caudal fin of the defeating one. After 2-3 days they became habituated to remain together and did not involve themselves in fighting.

Predation by Channa striatus (Bloch) on Rana tigrina (Daudin), Puntius gonionotus (Bleekeer) and Labeo rohita (Hamilton) in the laboratory

The growth performance of a predatory snakehead, Channa striatus was tested by supplying tadpoles of Rana tigrina and fingerlings of Puntius gonionotus and Labeo rohita as prey for a period of 21 days in aquaria. Prey consumption by C. striatus was significantly different (P<0.05) for different prey used (T1 - R. tigrina, T2 - P. gonionotus, T3 - L. rohita). Tadpoles of R. tigrina were preferred by the predator (C. striatus) over P. gonionotus and L. rohita although tadpole is nutritionally inferior to each of P. gonionotus and L. rohita. Each predator rayed on 50-330 mg per day per g of their body weight. Fish preyed on tadpoles also showed the highest growth. Significant difference in weight gain was found between T1 and T2 and also between T1 and T3 but no difference was found between T2 and T3. Food conversion ratio (FCR) was found to be lowest in treatment T3 followed by the treatments T2 and T1 respectively.

A study on the lipid distribution pattern in muscles of two teleosts, Arius dussumieri and Ophiocephalus striatus

The muscles of the various regions and zones of the body of the two teleosts, A. dussumieri and O. striatus have been analyzed for lipid contents. There is a significant dorsum-ventral gradient in lipid concentration exhibited by both the fishes with higher lipid values in the ventral aspect of the body, especially the belly flaps. As regards the vertical series, both the fishes exhibit comparatively higher lipid contents at the dorsal aspects of the caudal region and at anterior portion of the dorsal fin area with lower lipid values at cephalic and middle portions of the body. The red muscle of Arius exhibits higher lipid content than the white muscle.

Distribution of 5'-nucleotidase activity in the tissues of a freshwater teleost, Ophicephalus striatus Bloch

Homogenates of tissues have been analysed for the presence of 5'-nucleotidase activity. Sexes are not treated individually since no significant differences were observed. All organs showed marked activity, the highest being in the cardiac tissues, then the kidney, spleen, brain, and low values in the liver and muscles. Comparison with data from other fish studied shows a marked difference between O. striatus and O. punctatus.

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.

Hydrobiological studies of an irrigation tank with reference to the culture of large murrel, Channa marulius (Hamilton) and striped murrel Channa striatus (Bloch)

The importance of selection of species for culture according to the ecological niches and fish food organisms is highlighted with respect to the Fox Sagar, an irrigation take. The tank was infested with submerged vegetation as well as minnows and weed fishes, which rendered the tank unsuitable for the culture of Indian major carps. The tank was stocked with 8000 fingerlings of Channa marulius and C. striatus during 1981 by the local fisherman co-operative society. Only partial harvest was possible during 1982 because of high water level. The final harvest was in April-May, 1983. The yield obtained was 3640 kg during the culture period of about 20 months.

Studies on iced storage of common murrel (Channa striatus)

The iced storage characteristics of common murrel (Channa striatus) have been studied. The non-protein nitrogen and alpha amino nitrogen in the muscle of the fish decreased during iced storage and the total volatile base nitrogen at the end of iced storage was not high even though the fish became unacceptable during the period. There was steep decrease in total bacterial count during initial storages of storage and then increased steadily on further storage. The fish remained in acceptable condition for 8 to 9 days in ice.

Study on the growth and survival of Channa striatus (Bloch) postlarvae using live feed

Feeding experiments were conducted on the postlarvae of Channa striatus with two different live feeds - a copepod (Thermocyclops decipiens) and cladocerans (Moina micrura and Ceriodaphnia comuta) individually and in mixture. Food was provided at the rate of (500±50 Ind/L) and the experiments were carried out in 100 litre capacity tanks for 30 days. Results indicated better weight gain (951.85±28.77%) and survival (92.00<%) of postlarvae fed with mixed live food than individual live feed organisms.

A video method for quantifying size distribution, density, and three-dimensional spatial structure of reef fish spawning aggregations

There is a clear need to develop fisheries independent methods to quantify individual sizes, density, and three dimensional characteristics of reef fish spawning aggregations for use in population assessments and to provide critical baseline data on reproductive life history of exploited populations. We designed, constructed, calibrated, and applied an underwater stereo-video system to estimate individual sizes and three dimensional (3D) positions of Nassau grouper (Epinephelus striatus) at a spawning aggregation site located on a reef promontory on the western edge of Little Cayman Island, Cayman Islands, BWI, on 23 January 2003. The system consists of two free-running camcorders mounted on a meter-long bar and supported by a SCUBA diver. Paired video “stills” were captured, and nose and tail of individual fish observed in the field of view of both cameras were digitized using image analysis software. Conversion of these two dimensional screen coordinates to 3D coordinates was achieved through a matrix inversion algorithm and calibration data. Our estimate of mean total length (58.5 cm, n = 29) was in close agreement with estimated lengths from a hydroacoustic survey and from direct measures of fish size using visual census techniques. We discovered a possible bias in length measures using the video method, most likely arising from some fish orientations that were not perpendicular with respect to the optical axis of the camera system. We observed 40 individuals occupying a volume of 33.3 m3, resulting in a concentration of 1.2 individuals m–3 with a mean (SD) nearest neighbor distance of 70.0 (29.7) cm. We promote the use of roving diver stereo-videography as a method to assess the size distribution, density, and 3D spatial structure of fish spawning aggregations.