N Balakrishnan Nair

The annual reproductive cycles of Uca annulipes, Portunus pelagicus and Metapenaeus affinis (Decapoda: Crustacea) from the South-west coast of India

Employing the gonad index method, the reproductive cycles of three decapod crustaceans, Uca annulipes (Latreille), Portunus pelagicus (Linnaeus) and Metapenaeus affinis (Milne-Edwards) have been studied. In these crustaceans breeding is not continuous all the year round, but extends over several months of the year with distinct peak periods of gonadal activity. The male and female reproductive cycles are not concurrent. The peak of the reproductive cycle of males occurs slightly earlier in the breeding season than that of females. These studies indicate the possibility of production of successive broods of eggs during the same breeding season. In these species, the low saline conditions of the monsoon period are unfavourable for breeding. The medium and high saline conditions during the post-monsoon and pre-monsoon months, respectively, with plenty of planktonic food for the larvae, seem to be the favourable periods for breeding activity.

Effect of infestation with the isopod, Alitropus typus M. Edwards (Crustacea: Flabellifera: Aegidae) on the haematological parameters of the host fish, Channa striatus (Bloch)

Detailed accounts supported by experimental data are furnished regarding the haematological parameters of the host fish, Channa striatus infested by the isopod, Alitropus typus. Results demonstrate that the infested fish become anaemic through loss of blood as shown by a reduction in the total erythrocyte count, haemoglobin content and haematocrit. Considering the mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular haemoglobin concentration and volume index, the anaemia can be designated as macrocytic and hypochromic. The total and differential counts of white blood corpuscles of the infested fish indicate leucopenia coupled with lymphocytosis. The percentages of monocytes, neutrophils and macrophages, which were 0.65%, 0.39% and 1.04%, respectively, after 24 h of infestation, had increased to 2.31%, 4.91% and 2.02%, respectively, after 96 h of infestation and declined thereafter.

Preliminary observations on the interstitial fauna of the south-west coast of India

SummaryThis paper presents the preliminary observations on the interstitial fauna of the south-west coast of India, made during the course of 1963–1964. Observations were made at four stations representing different ecological habitats. The influence of some factors, such as wave action, grain size, temperature and salinity on the fauna was studied. The occurrence, seasonal abundance and the nature of distribution of the different groups on the intertidal zone, were also studied at the four stations.

Ecology of Indian estuaries—V: Primary productivity of the Ashtamudi estuary, south-west coast of India

Primary productivity at four representative stations in the Ashtamudi estuary has been presented. The average gross and net productivities in the surface water was maximum at Neendakara, the bar mouth zone and minimum at Kadapuzha, the riverine zone consistently exposed to pollution from paper mill effluents. Ashtamudi, the station directly on the gradient line and Kanjirakode, the station equidistant from Kadapuzha and Ashtamudi presented a transition phase with regard to the primary productivity. In the bottom water also productivity was minimum at the polluted zone. Generally productivity at sub-surface levels was higher than that at the surface. A seasonal pattern, independent of various environmental parameters, was discernible both in the gross and net productivity changes at surface and sub-surface levels. High concentrations of dissolved oxygen, silicate and nitrite helped to maintain higher productivities at Neendakara, Ashtamudi and Kanjirakode on several occasions during the year. The fact that productivity at the polluted Kadapuzha station was the lowest, indicates that the paper mill effluent has considerably disturbed the productivity mechanism of this otherwise healthy ecosystem.

Growth rates ofSalvinia molesta Mitchell with special reference to salinity

InSalvinia molesta Mitchell growth rate was uniform among the various size groups except in the proliferating floating stage in which it was faster. An average increase of about 25% weight occurred during a period of 5 days under laboratory condition. In general fresh set of leaves developed at an average interval of 4·5 days but this period may vary under different environmental conditions. In low salinities the growth of the fern showed retardation while in higher salinities it underwent complete destruction. Salinities above 7‰ was harmful for the weed while it completely withered in salinities 11‰ and above. Minimum period required for the total withering of the weed in salinities 34‰ and 11‰ were 30 min and 20 h respectively. These results are of value in the effective control of the weed by flushing them into brackish water lakes during monsoon.

The influence of salinity on a tropical estuarine shipworm Nausitora hedleyi Schepman (Bivalvia - Teredinidae)

Species belonging to the genus Nausitora (Bivalvia - Teredinidae) are generally confined to brackish waters. In the Cochin backwaters, a tidal estuary on the southwest coast of India, this genus is represented by the species N. hedleyi Schepman. Fresh settlement of the species in the area is noticed only during the period of low salinity, though the species of found to exist, throughout the year. Tests conducted to ascertain the effect of salinity changes on the activity of the borer showed that though it can endure a wide range, the optimum salinity range for early development was from 11.24–14.54%.

Ecology of biofouling on Crassostrea madrasensis (Preston) (Mollusca:Bivalvia) in a tropical backwater

Ecology of biofouling on the edible estuarine oysterCrassostrea madrasensis (Preston) has been investigated in the Ashtamudi Backwater of the southwest coast of India. Fouling was highly conspicuous throughout the year and dominant groups included barnacles, serpulids, bryozoans and modiolids. Intensity of fouling varied from 73 to 179 % on living oyster valves and 65 to 172 % on dead valves with respective annual averages of 118 and 127%. Substrate selection and settlement of the different groups were mostly opportunistic. Barnacles were the most dominant, living and dead ones collectively contributing to about 26 % of fouling on living valves and 32 % on dead valves. Serpulid fouling was 22 % both on living and dead oyster valves, bryozoans 15 and 12%, modiolids 11 and 12% and the miscellaneous groups formed 27 and 20 % respectively. Availability of free settling space and fouling in relation to substrate size were also investigated. Total fouling was very intense on oysters of 25–35 cm2 size group. Impact of biofouling on oysters and certain earlier studies on the topic are discussed.

Condition factor ofAmblypharyngodon chakaiensis Babu and Nair in the Chakai boat channel (Trivandrum-Kerala-India)

Condition factor (K) and relative condition factor (Kn) ofAmblypharyngodon chakaiensis Babu and Nair males and females respectively have been studied in relation to the various months of the year and length groups. No significant correlation exists between the proportion of the males in the population and value of condition factor (K). On the basis ofK andKn and the various length groups in respect of males and females are arranged into three classes and their incidence in the pre-spawning, spawning and post-spawning seasons were represented. In femalesKn showed significant positive correlation with gonadosomatic index. The size at first maturity observed by direct observation of the gonads in females and males agrees with the inflexions on the curve depictingK andKn with respect to length groups. The influence of feeding intensity onK does not seem to be quite apparent inA. chakaiensis. The steady fall inK in the males seems to be related to the decrease in the percentage occurrence of males of these length group in the sample.

Harpacticoid copepods associated with the seagrass Halophila ovalis in the Ashtamudi Estuary, south-west coast of India

A temporal study of harpacticoid copepod populations associated with the seagrass Halophila ovalis was undertaken in the Ashtamudi Estuary, south-west coast of India. A total of 19 species representing 8 families was recorded in this assemblage. Harpacticoids formed 7.52% of the total phytal meiofauna. At the species level, harpacticoids exhibit parallel assemblages with phytal zones, found in other localities.

Ecology of Indian estuaries: studies on the zooplankton ecology of kadinamkulam backwater

Ecology of the zooplankton of Kadinamkulam Backwater, a brackish water lake along the south-west coast of India, has been studied from February 1980-January 1981. Seasonal distribution of the zooplankton followed an uniform pattern throughout the backwater. Zooplankton in the Kadinamkulam Backwater is composed of foraminifers, coelenterates, nematodes, rotifers, chaetognaths, polychaetes, cladocerans, ostracods, amphipods, copepods, decapod larvae, insect larvae, bivalves, tunicates, and fish eggs and larvae. Among these, rotifers, copepods and copepod nauplii are the major components which form the bulk of the zooplankton (nearly 98 %). A distinct regional variation is discernible in the dominance of zooplankton components. Copepods constitute the dominant group near the barmouth and middle portion of the backwater, while rotifers are dominant in the upper reaches, where freshwater influx was relatively high. Factors influencing seasonal variation and distribution have also been discussed.