The bacteriology of oil sardine (Sardinella longiceps) and mackerel (Rastrelliger kanagurta) from tropical waters off Cochin. 2. Qualitative aspects

80% of the flora of skin, gills and intestines of oil sardine and mackerel at isolation temperature 28 ± 2°C consisted of Gram negative asporogenous rods or cocci, belonging to the genera Vibrio, Pseudomonas, Moraxella, Acinetobacter and Flavobacteria/Cytophaga. Nearly 10% of the flora was constituted by Gram positives, Micrococcus and Arthrobacter. Incubation temperature of 36 ± 1°C recovered more Vibrio spp. and Gram positives, while at lower temperatures of 8 ± 1°C and 1 ± 1°C, more Pseudomonas, Acinetobacter and Moraxella spp. were recovered. Significant changes with respect to season were observed in the relative distribution of different genera.

Mercury toxicity in two intertidal tropical marine molluscs

Lethal and sub-lethal effects of mercury have been studied in Perna viridis and Modiolus carvalhoi. For P. viridis LC30 is 1.0 p.p.m. at 48 h and 0.23 p.p.m. at 96 h. Recorded LC50 values for M. carvalhoi are 0.5 p.p.m. and 0.19 p.p.m. at 48 h and 96 h respectively. The results document that these two species, although inhabiting the same area in the tidal belt, exhibit clear differences in mercury resistance. It is further shown that the duration of exposure affects mortality rates. In sub-lethal concentration, between 0.01 and 0.10 p.p.m. decrease in pedal-gland activity is conspicuous in P. viridis. At concentrations much below LC50 values (at 96 h), although some animals are alive, pedal-gland activity is totally suspended, supporting the assumption that shell closure ability plays a minor role in byssus thread production. In M. carvalhoi total cessation of pedal gland activity occurred at 0.09 p.p.m. of mercury.

Salt tolerance of bacteria isolated from tropical marine fish and prawn

Salt tolerance of selected cultures of Pseudomonas, Moraxella, Vibrio, Micrococcus, Acinetobacter and Flavobacteria/ Cytophaga was determined. More than 80% of the cultures belonging to each of the above genera, were capable of growth in presence of 1.5 to 3.5% salt (NaCl) and at least 25 to 30% of the cultures in each group required 1.5 to 3.5% salt for growth. 40% each of Pseudomonas and Vibrio strains and 30% each of Moraxella, Micrococcus and Flavobacteria/Cytophaga strains tolerated 10% salt. Majority of the cultures belonging to the genera Pseudomonas, Vibrio, Moraxella, Micrococcus, Acinetobacter and Flavobacteria/Cytophaga were slightly halophilic (2 to 5% salt tolerant), about 25% especially of Micrococcus spp. moderately halophilic (5 to 20% salt tolerant) and none from Pseudomonas, Vibrio, Moraxella, Acinetobacter and Flavobacteria/Cytophaga spp. extremely halophilic (20 to 32% salt tolerant).