Early and better maturity in carp brood stock with control of environment and feeding

Available of carp breeders in their prim state of maturity is a major constraint in hypophysation. Experiments conducted in a fish farm at Naihati, West Bengal, for two consecutive years, 1983-84 and 1984-85, clearly prove that by manipulation of environmental parameters such as metabolites, dissolved oxygen, running water conditions, as also of stock densities and quality and quantity of feed. Catla catla, Hypophythalmichthys molitrix, Labeo rohita, Cirrhina mrigala and Ctenopharyngodon idella can be made to attain better maturity and spawning stage much earlier than normal i.e. even in summer months and the entire stock spawned during the period from March to September. Percentage of successful breeding, quantities of eggs released and fertilised in relation to the body weight of all the species, were also found to be more in comparison to the brood stock raised through the conventional methods.

A study on length-weight relationship, food and feeding habits of Indian scad, Decapterus russelli (Ruppel, 1830) along the northwest coast of India

Length and weight relationship of Decapterus russelli (Ruppell, 1830) is worked out to be W = 0.00312 L³ which indicates the isometric growth of the fish. Study on food and feeding habits revealed that the species is carnivorous, pelagic, feeding primarily on small crustaceans and small fish species, viz. Acetes indicus, ostracods, Apogon sp., Leiognathus sp., sciaenids, Netnipterus japonicas, Myctophid sp., Trichiurus sp., Therapon sp., D.russelli and occasionally on prawns. It is a selective feeder on Aeetes indicus.

Mixed culture of fishes in seasonal ponds through fertilization and feeding

A study on mixed culture of mirror carp (Cyprinus carpio Lin.), tilapia (Oreochromis niloticus Lin.), silver carp (Hypophthalmicthys molitrix Val.) and Thai sharpunti (Puntius gonionotus Bleeker) in the ratio of 1:2:2:5 was conducted in 12 seasonal mini ponds (30 m² each) for 105 days. There were six treatments each with two replicates and each pond was stocked with a total of 100 fishes. Rice bran and mustard oil cake were used as supplemental feed either in combination or alone in presence or absence of fertilizer. Fertilizers were used in the form of organic, inorganic or both. The best growth performance of mirror carp, tilapia and Thai sharpunti was obtained in treatment III which received both fertilizer (organic+inorganic) and rice bran while the highest growth of silver carp was obtained in treatment VI receiving only inorganic fertilizer. However, the overall best production (2450 Kg/ha) and economic return for the culture period was obtained in treatment VI followed by treatment III. The results are discussed in the light of water quality parameters.

Rearing of catfish (Clarias batrachus Lin.) larvae with live and prepared feeds

Provision or live feed (Tubificid worms) attributed significantly better weight gain in the five days old Clarias batrachus larvae when reared for another 28 days compared to those fed mixed feed (live and artificial) and artificial feed only. Larvae fed mixed feed showed significantly better weight gain compared to those fed only artificial feed and the survival rate was similar to those fed only live feed. Both the weight gain and survival rate were the lowest for the larvae reared only on artificial feed.

Effects of supplementary feeds on growth and survival of freshwater giant prawn (Macrobrachium resenbergii [i.e. rosenbergii] deMan)

Highest growth of prawn was obtained with Feed B (743 kg/ha) with highest survival rate (60.88%) followed by Feed A where production and survival rate was 659 kg/ha and 53.50%, respectively. Feed A contained 30% dry ground cow viscera, 40% oil cake, 20% rice-bran and 10% heat bran. Feed conversion ratios were found to be 7.60:1 for Feed A and 6.46:1 for Feed B, which indicated that Feed B was more efficiently utilized by the prawn than Feed A. Statistical analysis revealed that the differences in production of prawns among the treatments were highly significant (P< 0.01).

Effects of artificial feeds on production of fishes in polyculture

A study on the effects of artificial feeds on the growth and production of fishes in polyculture in 6 ponds along with some limnological conditions was conducted. Species of Indian and Chinese major carps (Labeo rohita, Catla catla, Cirrhinus mrigala, Hypophthalmicthys molitrix) and catfishes (Clarias batrachus, Clarias gariepinus) were stocked in 6 ponds. Stocking rate in both cases were 32044 fingerlings per hectare. Ratio of species of Rui:Catla:Mrigal:Silver carp:African Magur:Local Magur=25%:25%:5%:25%:14%:6%. Fertilization and artificial feeds were given in 3 ponds (treatment I) and only fertilization was done in other 3 ponds (treatment II). Average yield/ha/yr was 7.903 m.ton in case of fertilization and artificial feeding application and 3.374 m.ton in case of only fertilization application. Urea, TSP and cow dung were applied fortnightly at the rates of 400 kg/ha/yr, 2000 kg/ha/yr and 4000 kg/ha/yr respectively. Wheat bran, rice bran and mustard oil cake were given daily as an artificial feed in treatment I. Whereas treatment II was conducted without any artificial feed. Ratio of artificial feed was wheat bran:rice bran:oil cake=2:2:1 (by wt). Absence of artificial feed in 3 ponds under treatment II seriously affected the growth and production of fish.

Development of a new model of feeding strategy analysis of fish incorporating resource availability and use data

A feeding strategy model is proposed using stomach content and resource availability data as a modification to Costello (1990) and Amundsen et al. (1996). Incorporation of feeding electivity index (E) instead of the prey-specific abundance signifies the importance of resource availability in prey selection as well as the predator's ability to specialize, generalize or avoid particular prey items at the individual and population level.

Niche measures and feeding strategies of Barbodes gonionotus Bleeker and Oreochromis spp. from a ricefield in Bangladesh

Intra-and interspecific virtual niche measures and feeding strategies of Barbodes gonionotus and Oreochromis spp. were studied from a rice field in Bangladesh. Appropriateness and ease of interpretation of different indices were evaluated. Small sizes of both species had a relatively wider dietary breadth and used many of the resource categories available to them than the large size groups, though none were generalist feeder. The dietary overlap of large B. gonionotus on the small was greater than the reverse, but biologically insignificant. While the dietary overlap of large Oreochromis spp. on the small was significantly greater. Interspecific dietary width was relatively broader for B. gonionotus than Oreochromis spp. and overlap of B. gonionotus on Oreochromis spp. was significantly greater than the reverse. Evidence of significant intraspecific dietary overlap between the two sizes of tilapia reflects strong competition and cautions for mixed-size stocking in rice-fish system. Besides, there seem fewer opportunities for habitat segregation between B. gonionotus and Oreochromis spp., due to the significant interspecific dietary overlap of the former on the latter in rice-fish system. Tilapia specialized on periphytic detrital aggregate while silver barb tended to consume aquatic macrophytes and molluscs. Small sizes of B. gonionotus should be preferred for rice-fish integration over the Oreochromis spp. due to their broader niche width and pronounced ontogenetic dietary shifts with the aging of the stock.