Eradication of predatory fishes in fish ponds and nursery ponds using electricity

Prior to stocking economic species in tanks and nursery ponds, all the unwanted and predatory fishes in them will have to be removed. Even though most of them can be caught with ordinary gear such as cast net, drag net, scoop net etc. Total or absolute eradication is not possible and those left over are sufficient to destroy all the fingerlings introduced. Development of an electrical method for killing predatory fishes at reasonable cost is therefore, expected to provide a solution. This paper deals with a few methods, based on the use of electricity and which are suitable for different ponds.

Utilization of the fish waste self-brine of fish curing industry as farm fertilizer

Large quantities of self-brine accumulating in curing tanks during the process of commercial fish salting is mostly wasted at present. This liquor exuded from the fish during the process of salting contains considerable amounts of soluble proteins and minerals. Due to the presence of organic matter the self-brine quickly putrefies causing nauseating smell. This renders the whole surroundings insanitary and often leads to health hazards to neighboring localities. Any economic method of utilising this waste brine and converting it into some useful product will be a tangible help to the fish curing industry. Hence, a method is given for converting this waste self-brine into a cheap and efficient fertilizer.

Identification and culture of common diatoms as possible feed for Penaeus monodon

Diatoms were collected from Buyuan Bay, and from the hatchery tanks at Tigbauan, to determine the commonly occurring species, the feasibility of culturing these species, and the potential of these selected species as food for larval P. monodon. The commonly occurring diatoms were identified as Chaetoceros calcitrans, Navicula grimmei, Nitzchia seriata, Nitzchia closterium and Amphiprora sp. These diatoms were isolated and unialgal cultures prepared. Protein content analysis using the micro-Kjildahl method gave the following result: C. calcitrans, 11 . 78%; Nitzchia seriata, 25%; Nitzchia closterium, 30 . 5%; Navicula grimmei, 9 . 06% and Amphiprora sp. 8 . 96%. Feeding experiments were conducted to determine acceptability of the different diatom species and percentage survival of larval stages Z SUB-1 -M SUB-2 . Larvae were placed in 4-l capacity plastic containers with a stocking density of 10/l. The results of several feeding trials using the different mass-produced diatoms are summarized. From the data gathered, C. calcitrans appears to be the most promising candidate as feed for zoea and mysis stages of P. monodon. The average percentage survival of C. calcitrans was 63 . 76% for the 3 trials, and as high as 82 . 22% in the third trial. Comparatively high percentage survival of larvae was also recorded when Nitzchia seriata (48 . 17%) and Nitzchia closterium (67 . 6%) were given as feed, while both Amphiprora sp. and Navicula grimmei gave 0% survival. The poor results with Amphiprora sp. and Navicula grimmei may be due to their low protein content (8 . 96% and 9 . 06%, respectively) and the inability of the larvae to ingest them. Navicula and Amphiprora were observed to cling to the appendages of the larvae and to settle down in the medium making them unavailable to the larvae. Low survival was also noted when frozen C. calcitrans was used (14 . 25%). This may be due partly to the effect of the floculating agent (ALSO SUB-4 . 25 g/l) used in concentrating the diatoms. When protein contents of C. calcitrans, N. seriata and N. closterium are compared, the 2 Nitzchia species have relatively higher protein contents than C. calcitrans and, therefore, could be the more desirable feed candidates. However, few feeding trials were made using Nitzchia so that additional investigations will have to be done on this aspect.

A suctorean parasite of Penaeus monodon larvae

A pathogenic suctorean, identified as Ephelota gemmipara was observed in P. monodon larvae spawned and reared in tanks. Commonly found to inhabit hydroid colonies, E. gemmipara has a stalked body with two types of tentacles, the sucking and piercing types, and was observed to reproduce by multiple exogenous budding.

Effect of furanace on the development of larval stages of Penaeus monodon Fabricius

Zoea 2(Z SUB-2 ) Mysis 1 (M SUB-1 ) and Postlarva 1 (P SUB-1 ) of P. monodon artificially spawned in closed-system concrete hatchery tanks were bioassayed for their tolerance to the antibiotic furanace. The setup consisted of four 20-liter capacity plastic basins previously conditioned for 15 days with freshwater in full sunlight. During the experiment, each basin was filled with 5 liters of seawater to which was added filtered Chaetoceros and Brachionus to give densities of 5 . 0-7 . 5 x 10 SUP-4 cells/ml and 10-20 individuals/ml, respectively. The following are the properties of the water used throughout the experiments: salinity, 26-32%; pH, 7 . 3-8 . 4; temperature, 25-30 degree C; dissolved oxygen, 4 . 5-8 . 4 ppm; nitrite, 0 . 36-0 . 99 ppm; and ammonia, 0 . 10-0 . 30 ppm. To each basin were added 50 healthy larvae of specific stages of P. monodon. After an initial acclimation of one hour in the medium, preweighed amounts of the antibiotic were added and thoroughly dissolved. The concentrations tested were 1 . 0, 2 . 0 and 3 . 0 ppm. One basin always served as control. After 24 hours of exposure, the surviving population in each basin was counted. The survivors were then examined thoroughly under the microscope for unusual behavior and morphological defects brought about by the exposure. To minimize wide variations in the medium as a result of feeding and other manipulations, the systems were all prepared at 9:00 a.m. each time, and the feeds on two instances, one at 5:00 p.m. and another at 5:00 a.m. Fifteen trials conducted with Z SUB-2 showed survival ranges of 68% to 98% with a mean of 77 . 6% in the controls; 32% to 94% with a mean of 65 . 7% at 1 ppm, and 0% to 56% with a mean of 36 . 5% at 2 ppm. There were no survivors at 3 ppm. Interpolation from the survival-dose curve gave a 24-hr LC SUB-50 of approximately 1 . 6 ppm.

The biology and control of Caligus sp., an ectoparasite of the adult milkfish Chanos chanos Forskal

One unidentified species of copepod belonging to the genus Caliqus of the family Caigidae was found to infest the adult milkfish broodstock. To control the parasites infesting the adult milkfish, tests were made using the chemical (2,2,2-trichloro-1-hydroxyl)-phosphonic acid-dimethylethol (Neguvon) at a concentration of 0 . 25 ppm. It is noted that a concentration of 0 . 25 ppm of Neguvon maintained for 12-24 hours in the sabalo-containing tanks in a closed water system but with aeration is effective in controlling the parasites. Fish mortality during the experiment was due to inadequate aeration in the tanks.

Land-based mass production of prawn (Penaeus monodon Fabricius) spawners

The first spawnings were obtained 12 days after ablation with 4 spawners yielding 784,000 eggs and a harvest of 250,000 P SUB-10 fry. Survival of females after 1 month was approximately 30%. Mortalities were mostly due to handling stress during the regular ovarian samplings as well as disease frm the accumulated excess feeds on the bottom of the tank. Male survival could not be recorded because of transfers to other tanks and addition of new stocks. Development seemed to peak 3 weeks after ablation. The average number of eggs per ablated spawner was 120,000. However, many of the partially spawned females were removed from the spawning tanks the following day so that remaining eggs released in the next 2 to 3 days could not be recorded. Estimate of the average number of eggs per ablated spawner is 120,000-150,000 in contrast to 500,000 per wild spawner. However, the low production cost more than compensates for the difference. Fry reared in the Wet Laboratory were used for experiments, mostly on feeding. Therefore, survival at harvest is not to be taken as a reflection of stock quality. Although fewer in number, larvae from ablated prawns are as healthy in terms of vigor in swimming and feeding as those from wild females. Most mortalities are due to inability to molt caused by lower water temperatures and inadequate feeding.

Minimum dissolved oxygen tolerance of four different sizes of milkfish

Four size groups of milkfish were tested, 4-18 g, 20-34 g, 35-95 g and 200-300 g. A number of fish from each group were placed separately in identical 1.2 m2 wooden tanks containing seawater filled up to 30 cm depth. The aggregate weight of fish per size group was approximately 1 kg. The fish were held for 72 h, fed with lab-lab and provided with continuous aeration to allow recovery from stress during transport and handling. After the recovery period, aeration was stopped and 200 g of the fine rice bran was spread over the water in each tank creating a film of bran particles on the water surface. This was designed to speed up depletion of dissolved oxygen considering the combined effects of the screening-off of sunlight, the reduction of air-water interface and the breakdown of the bran particles. It is probable that stress on milkfish in brackishwater ponds could start when oxygen level drops to about 1.4 ppm. A further decrease to 0.04 ppm could produce a total kill of all specimens above 4 grams with marketable size and bigger size fish dying first.

Effect of substrate types on fecundity and nauplii production of ablated Penaeus monodon Fabricius

Experiments were undertaken to assess the survival, spawning, fecundity and nauplii production of ablated P. monodon females reared in flow-through broodstock tanks with white coralline and black sand substrate for 62 days. The similar trend observed in mortality rates in both substrates suggests that variation in substrate material for broodstock tanks is not a likely cause of prawn mortality. There were also no significant differences observed between rematurtion rates, i.e. number of spawnings, under the different treatments. Singnificantly higher nauplii production were observed in females in tanks with white substrates. At present, the land-based broodstock tanks in SEAFDEC utilize white coralline substrates due to higher hatching rate of eggs and nauplii production, convenience in siphoning out debris and excess food that tend to accumulte in the tank, and contrast provided by the white substrate during nightly observations of ovaries.

Salinity preference of the milkfish Chanos chanos Forskal

Salinity preference of the milkfish fry is described. Milkfish fry which were acclimatized to different salinities have preference for certain salinity which is 32 ppt. Majority of the fry in the control tanks usually prefer to stay either at the bottom or at the uppermost layer; only a few stay at the middle layer. This strongly suggests that milkfish fry that are not caught along the shore by fishermen usually tend to migrate to waters of high salinity. Furthermore, salinity preference of milkfish fry does not change with age.

Effect of different sex ratios of ablated wild-stock Penaeus monodon Fabricius on maturation, fecundity and hatching rates

The study was conducted to determine other sex ratios of ablated wild-stock Penaeus monodon other than the most commonly practiced 1 male: 1 female. Four different sex ratios, 0:1, 1:1, 1:2, and 1:4 male: female were tested in four 4m diameter circular tanks for a period of 55 days. During the first run the 1 male: 2 females ratio gave: (a) the highest percentage of first (42.20%), second (30.00%) and third (33.33%) spawning; and (b) the highest total and average fecundity (3.9 million eggs and 300,692 eggs, respectively). The 1 male: 2 females ratio is recommended on the basis of highest percentage for the first, second and third spawners, total and average fecundity.

Survival, maturation, fecundity and hatching rates of unablated and ablated Penaeus indicus H.M. Edwards from brackishwater ponds

Penaeus indicus harvested after three months of rearing in brackishwater ponds and averaging 6.9 g for females and 5.6 g for males were stocked in two 12 cu m flowthrough ferrocement tanks at 240 females and 200 males per tank. The females were ablated on one eyestalk in one tank and remained unablated in the other tank; all males were unablated. Ablated females spawned up to 7 times per female; unablated females spawned up to only 3 times during the two month duration of the experiment. Ablated females produced a total number of 17.5 x 10⁶ eggs, 6.6 x 10⁶ nauplii, and an average of 23,480 eggs/spawning and 37.8% hatching rate from a total of 757 spawnings. Unablated females produced a total of 2.0 x 10⁶ eggs, 1.1 x 10⁶ nauplii, and an average of 26.990 eggs/spawning and 53.9% hatching rate from a total of 74 spawnings. Survival of ablated females was 53.5% compared to 69.4% for unablated females; males in both tanks averaged more than 90% survival.

A comparative study on the induced breeding and in vitro fertilization performance by various inducing agents in catfish, Heteropneustes fossilis (Bloch)

Brood catfish, Heteropneustes fossilis were collected from Tamirabarani river basin of Tamil Nadu, India and kept in cement tanks. Three inducing hormones viz, Ovaprim, Ovatide and WOVA-FH were injected at the rate of 0.5, 1.0, 1.5 and 2.0 ml/kg body weight in order to induce oocyte maturation and ovulation. After 10-13h of injection at a water temperature of 27±-0.5°C, stripping of eggs and in vitro fertilization was done. Ovaprim gave maximum (94.67%) hatching rate followed by Ovatide (90.33%) and WOVA-FH (77.33%).

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.

How to construct a fish smoking kiln

As interest increases in fish production, fish farming is on the rise as more fish is produced in ponds, cages and tanks. However not all fish can be sold out and consumed at the same time, in addition to this, different consumers show different preference. Some individua Is tend to prefer smoked fish to fresh and fried fish. Apart from satisfying the different consumer preferences, fish smoking is important because it in creases the self life of fish, there by reducing post harvest losses. It also adds value to the fish and in this way the farmer can fetch more money from farmed products. Although the technology has been around for several years amongst the fishing communities, it is not well known amongst fish farmers. There is need to bring fish fanners on board to know how to construct the smoking kiln through the stapes out lined below.