Heavy infection of Ichthyophthirius multifiliis in striped catfish (Pangasianodon hypophthalmus,Sauvage 1878) and its treatment trial by different therapeutic agents in a control environment

ABSTRACT

Striped catfish (Pangasianodon hypophthalmus) fingerlings were stocked (60 fishes/m³) in cemented square tanks for ornamental fishery purposes at the College Fish Farm in Mangalore. A total of 400 fishes with a mean weight (g) ranging from 3.24 ± 1.21 to 6.70 ± 1.13 and a mean length (cm) of 7.50 ± 0.94 to 9.50 ± 1.10 were examined. A severe outbreak of salt-like granule white spots was found on the body surface. Ichthyophthirius multifiliis, a ciliate pathogen, was identified as the causative agent by clinical signs, wet mount, and histopathological observations. Infected fishes were transferred and equally distributed to the 0.45 m³ glass aquaria and treated with three treatments: (T1) methylene blue + salt; (T2) raising temperature with salt; and (T3) formalin + malachite green. The best fingerling survival (55 ± 9.36%) was obtained by elevated water temperature with salt in T2.     

Seasonal and interannual variations of oceanographic conditions off Mangalore coast (Karnataka, India) in the Malabar upwelling system during 1995–2004 and their influences on the pelagic fishery

Mangalore coast is well known for its multi‐species and multi‐gear fisheries and the fishery and oceanographic features of this region is a true representation of the Malabar upwelling system. Ten years of study (1995–2004) of oceanographic parameters has been carried out from the inshore waters off Mangalore to understand their seasonal and interannual variations and influences on the pelagic fishery of the region. Attempt has been also made to understand the influence of local and global environmental conditions on the alternating patterns of abundance between the Indian mackerel and oil sardine from the area. Field‐ and satellite‐derived oceanographic data have shown that coastal upwelling occurs during July–September with a peak in August resulting in high nutrient concentrations and biological productivity along the coast. Nearly 70% of the pelagic fish catch, dominated by oil sardine and mackerel, was obtained during September–December, during or immediately after the upwelling season. Catches of scombroid fishes were significantly related to cold Sea Surface Temperature, while such relationships were not observed for sardines and anchovies. Significant positive correlations were observed between the ENSO events (MEI) and seawater temperature from the study area. The extreme oceanographic events associated with the cold La Niña, which preceded the exceptional 1997–98 El Niño event, were responsible for the collapse of the pelagic fishery, especially the mackerel fishery along the southwest coast of India (Malabar upwelling system). Coinciding with the collapse of the mackerel fishery, oil sardine populations revived during 1999–2000 all along the southwest coast of India. Tolerance of oil sardine to El Niño / La Niña events and the low predatory pressure experienced by their eggs and larvae due to the collapse of mackerel population might have resulted in its population revival.     

Reproductive biology of ridgeback shrimp Solenocera choprai (Decapoda, Penaeoidea, Solenoceridae) off Mangalore coast, south India

Abstract:   The ridgeback shrimp Solenocera choprai has emerged as one of the important commercial species in 60–100 m depth zone off Karnataka coast, India, since 1993. Studies were conducted on S. choprai to understand its reproductive biology which can help in formulating policies for management of the species. The diagnostic features of reproductive morphology of the species were studied and illustrated in detail. Based on the coloration and size of the ovary and ova diameter variations, five stages of maturity in female S. choprai were identified. The mature ova are fully yolked with diameters between 0.24 and 0.35 mm. Size at maturity (50%) has been estimated at 54.5 and 66.5 mm total length (TL) in males and females, respectively. The gonadosomatic index (GSI) showed an increasing trend according to the advancement of maturity of the ovary, and monthly mean GSI showed a positive correlation with monthly percentage of spawners. Solenocera choprai was found to be a continuous breeder with two peaks: a major peak in November and another extended peak during January–February. The estimated numbers of ova in the mature ovary were 38 532 and 133 689 in shrimps measuring 80 and 110 mm TL, respectively. A sigmoidal increase in the female-to-male sex ratio with increase in size was noticed in the species. A χ ²-test showed that the annual distribution of females and males is not significantly different from a 1:1 ratio at the 1% level.