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19892
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Subject: Aquaculture × End date: 1989 × Start date: 1989 × Type: Thesis × Thesis Type: M.Sc ×
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    ThesisItemOpen Access
    Effect of salinity on survival, growth and breeding of the shrimp
    (Department of Aquaculture, College of Fisheries, Panangad., 1989) Ignatius, C A; KAU; Thampy, D M
    The present study has been undertaken with the major objective of elucidating the effect of salinity on survival, growth, ovarian development, fecundity, incubation period and batch hatching of the freshwater prawn Macrobrachium idella. Mortality of juveniles of M. idella which were acclimated at 0 and 20 ppt and treanferred abruptly to varying salinities, was found to start at 27.5 and 32.5 ppt respectively, whereas in those which were gradually acclimated from 0 to 45 ppt, it was found to start only at a higher salinity level of 37.5 ppt. The 120 Hr LC50 values were 30.90 + 0.7107, 35.89 + 0.7842 and 40.74 + 0.7402 ppt for the prawns acclimated at 0 and 20 ppt and for those gradually acclimated respectively. Thus it could be seen that this prawn is a highly euryhaline one and that acclimation at a higher salinity level and gradual acclimation have got advantage in extending the upper tolerance level. Growth was found to be significantly influenced by salinity, being highest at 0 – 10 ppt, lower at 15 ppt and almost nil at 20 ppt and beyond. Sporozoan infection was noticed in the prawns reared at 15, 20 and 25 ppt. Salinity was found to have no significant influence on fecundity, while ovarian development is being influenced by it. The rate of ovarian development was high at 6 and 12 ppt and low at 0 ppt. Incubation period, which takes about 13 – 15 days was not found to be influenced by salinity, while there was some effect on batch hatching, the rate of which was more at 0 ppt and less at 6 ppt. During incubation, mortality of eggs due to infection was observed only at 0 ppt. Thus, it could be seen that a salinity level of around 6 ppt is ideal for ovarian development, maximum fecundity and synchronous hatching.
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    ThesisItemOpen Access
    Food selectivity of pond reared and wild Etroplus suratensis (Bloch) and effect of supplementary feeding on its growth
    (Department of Aquaculture, College of Fisheries, Panangad, 1989) Sathiavathy, C R; KAU; Susheela, Jose
    Food and feeding habits of E.suratenis during fry (30-49 mm), fingerlings (50-69) mm, subadult (70-89 mm) and adult (90-120mm) stages in the captive environment of a culture pond and wild environment viz. Cochin backwater were studied. The study was conducted from October 1986 to March 1987. A culture pond in the College of Fisheries, Panangad was stocked with E. suratensis of the above four length groups in 1:1:1:1 ratio, at a stocking density of 5600 Nos/ha, after preliminary preparations. Samples were collected from both these environments form the end of first month onwards. Each month, the numbers that were removed from the culture pond were restocked with same numbers of specimens of various length groups. Salient ecological parameters viz, temperature, PH, salinity, alkalinity,dissolved oxygen,phytoplankton primary productivity, zooplankton and zoobenthos of the culture pond and the backwaters were analysed at monthly intervals . The feeding intensity of the specimens in the captive and wild environment, relative lengths of gut during different stages, food items consumed in the culture pond and in the backwaters and selectivity index of various food items were studied. A feeding experiment was also conducted with fingerlings of E. suratensis where five feeds were used in duplicate. The feeds used were (I) conventional feed made of groundnut oil cake and rice bran (1:1) having 31.50% crude protein (II) 50% conventional feed + 50% fresh hydrilla verticillata having 24.55% crude protein (III) Fresh Hydrilla verticillata alone having 17.60% crude protein (IV) 50% conventional feed + 50% fresh Enteromorpha intestinalis having 23.30% crude protein (V) fresh Enteromorpha Intestinalis alone having 15.1% crude protein. Analyses of the physio-chemical parameters of the captive and wild environments show that their range was tolerable for the normal life activities of fishes and did not affect the food intake of the species. The feeding intensity of E.suratensis was found to increase from the first length group to the fourth length group in both the environments. The feeding indices of the four different length groups in the brackish water culture pond were 13.89, 19.45, 33.33 and 44.44 while the corresponding values in the backwaters were 55.56, 66.67, 72.72 and 77.78. Feeding intensity of E.suratensis was higher in the backwaters than in the culture pond. The RLG of E.suratensis from first to fourth length groups in the culture pond were 2.911, 3.111, 3.850 and 4.420 while the corresponding values for the fishes form the backwaters were 3.011,3.331, 4.010 and 4.535. The food items in general of the four length groups in culture pond were detritus, diatoms, filamentous algae, rotifers, copepods, other crustaceans, insect larvae and gastropods, with some variations in their order of preference among different length groups. In the backwaters the major food items in general were diatoms, higher aquatic plants, detritus , rotifers, copepods, other crustaceans and insect larvae. Selectivity index of the important food items in the culture pond and backwaters during October 1986 and March 1987 were studied for all the length groups. Selectivity index values were obtained for diatoms, filamentous algae, rotifers, copepods, other crustaceans and insect larvae for all the for length groups in pond and backwater. The selectivity index of detritus was +1 for all the four length groups in culture pond and backwaters, during both the months under study. For the higher aquatic plants, the selectivity index was +1 for the length groups II, III and IV in the backwater. But for the length group I in the backwaters and for all the four length groups in culture pond, no selectivity index exist for higher aquatic plants. In the feeding experiment, maximum values for average specific growth rate expressed as percentage wet body weight d-1 (0.455), average monthly increment (39), percentage gain in the body weight (14.634%) and best food conversion factor (18) were obtained for feed V, viz; fresh Enteromorpha intestinalis alone. Statistical analysis using analysis of variance technique showed that there was significant variation due to the effect of feeds. Analysis of least square method indicate that these five feeds can be grouped into two. In the first group, with feeds I and II, there was no significant difference between the feeds. In the second group with feeds III, IV and V , no significant difference were seen among themselves, but all these feeds show significant difference with the feeds I and II. The growth performance obtained by these feeds in the second group were superior that the feeds I and II.