by
A. SREENIVASAN
Fresh-water Biological Station
Bhavanisagar, India
APPLICATION OF LIMNOLOGICAL AND PRIMARY PRODUCTION STUDIES IN FISH CULTURE
Abstract
Limnology, primary production, and fish yield in five aquatic biotopes were studied. Odathurai tank, a small 50 ha impoundment with continuous inflow and outflow exhibiting very little diurnal variations in chemical parameters, was poor in plankton and the primary production was the lowest of the five types of waters: 1.75 to 6.83 g 02/m2/day. In K.C. Kulam pond and Chinglepet fort moat, wide diurnal variations in alkalinity and dissolved oxygen were noted but depth variations were little. The pH value varied widely as a result of intense photosynthetic activity in Chinglepet fort moat. Vellore fort moat was very similar to these two waters and in addition variations related to depth were also noted in dissolved oxygen, alkalinity and pH, indicating very strong, tropholytic activity in the bottom. The temple pond ‘Ayyankulam’ resembled Vellore fort moat in marked diurnal and depth variations in dissolved oxygen, alkalinity and pH. Community respiration was very high in Vellore fort moat and K.C. Kulam pond and least in Odathurai tank. Metabolic activities, as indicated by changes in dissolved oxygen, alkalinity, respiration, etc., were well correlated with gross primary production. These are also correlated with other parameters such as hardness, electrical conductivity, calcium, chlorides, phosphate, silicate and plankton. By using the limnological data and the diurnal and depth variations in chemical parameters, it is possible to predict the relative productivity of aquatic biotopes.
EXEMPLES D'ETUDES DE LIMNOLOGIE ET DE PRODUCTION PRIMAIRE APPLIQUEES A LA PISCICULTURE
Résumé
Des études de limnologie, de production primaire et de production de poisson ont été effectuées dans cinq biotopes aquatiques. Le réservoir d'Odathurai, pièce d'eau de 50 ha caractérisé par une alimentation et un écoulement continuels ainsi qu'une très faible amplitude des variations diurnes des paramètres chimiques, s'est révélé pauvre en plancton: la production primaire était la plus faible de toutes celles enrégistrées dans les cinq types d'eau: 1,75 à 6,83 g O2/m2/jour. Dans l'étang de K. C. Kulam et dans le fossé du fort de Chinglepat, on a constate que le degré d'alcalinité et la teneur en oxygène dissous, présentaient d'importantes variations diurnes mais variaient peu avec la profondeur. Dans les eaux de Chinglepat, le pH accusait de fortes variations par suite d'une photosynthèse très active. Le fossé du fort de Vellore présente de fortes analogies avec les deux pièces d'eau précitées et, en outre, on y a noté des variations en profondeur de la teneur en oxygène dissous, de l'alcalinité et du pH, ce qui indique une très forte activité tropholytique sur le fond. L'étang du temple d'Ayyankulam présentait les mêmes caractéristiques que le fossé du fort de Vellore en ce qui concerne l'amplitude marquée des variations diurnes et en profondeur de la teneur en oxygène dissous, de l'alcalinité et du pH. La respiration communautaire était très élevée dans le fossé du fort de Vellore et dans l'étang de K. C. Kulam et le plus faible dans le réservoir d'Odathurai. Les activités métaboliques, mesurées par les modifications de l'oxygène dissous, de l'alcalinité, de la respiration etc., correspondaient bien à la production primaire brute. Ces phénomènes ont également été mis en corrélation avec les autres paramètres tels que la dureté, la conductivité électrique, le calcium, les chlorures, les phosphates, les silicates et le plancton. En partant des données limnologiques et des variations diurnes et en profondeur, il est possible de prévoir la productivité relative des biotopes aquatiques.
APLICACION EN LA PISCICULTURA DE LOS ESTUDIOS LIMNOLOGICOS Y DE LA PRODUCCION PRIMARIA
Extracto
Se han llevado a cabo estudios limnológicos y de la producción primaria así como del rendimiento de peces en cinco biotopos acuáticos. El estanque de Odathurai, pequeño embalse de 50 hectáreas con constante entrada y salida de agua muestra variaciones diurnas muy pequeñas de los parámetros químicos, escasez de plancton, y su producción primaria fué la menor de los cinco tipos de aguas: 1,75 a 6,83 g 02/m2/día. En el estanque de K.C. Kulam y en el foso del fuerte de Chinglepat se observaron amplias variaciones de alcalinidad y del oxígeno disuelto si bien las variaciones de profundidad eran pequeñas. El valor del pH varió ampliamente como resultado de una intensa actividad fotosintética en el foso de Chinglepat. El foso del fuerte de Vellore fué muy semejante a dichas dos aguas y además se observaron, relacionadas con la profundidad, del oxígeno disuelto, de la alcalinidad y del pH, lo que indicaba una actividad trofolítica muy intensa en el fondo. El estanque del templo de Ayyankulam se parecía al foso del fuerte de Vellore en las sensibles variaciones del oxígeno disuelto, la alcalinidad y el pH, tanto diurnas como debidas a la profundidad. Las actividades metabólicas, señaladas por los cambios de oxígeno disuelto, alcalinidad respiración, etc., se correspondieron bien con la producción primaria bruta. Estas están igualmente correlacionadas con otros parámetros tales como la dureza del agua, la conductividad eléctrica, calcio, cloruros, fosfato, silicato y plancton. Utilizando los datos limnológicos y las variaciones diurnas y de profundidad en los parámetros químicos es posible predecir la productividad relativa de los biotopos acuáticos.
The paramount need to increase protein supply to the inland population has necessitated the use of all available waters for fish culture. Even waters unsuitable initially could be improved to make them fit for fish culture. Despite the intensification of pond culture, adequate accounts of limnological aspects are not available. As part of a program to correlate the biological cycles in ponds with fish production in India a few ponds in Madras state have been studied intensively and the results are presented here.
Ponds were sampled periodically, the water being collected by a Friedinger sampler. The oxygen method (dark and light bottles) was used to estimate primary production as indicated in previous papers (Sreenivasan, 1964a,b,c). The water samples collected were analysed for dissolved gases, dissolved nutrients, etc. according to standard methods, within a few minutes of collection.
(i) Vellore fort moat
The Vellore fort moat is an L-shaped pond surrounded with vertical stone walls and 4.8 ha (12.0 acres) in area. It is supplied with the storm-water drainage of the town along with some sewage. Further, direct faecal pollution also occurs. This pond accumulates a lot of fine ooze because it is not completely drained and the outlet is 4.0 m above the bottom. The average depth is 1.5 m, the maximum depth 4.0 m.
(ii) Ayyankulam
This is a typical temple tank, 1.4 ha, with stone-paved steps all round. This is used only for bathing by people and for washing clothes. It is also filled by storm water after rains. The water is less polluted than Vellore moat. The average depth is 3.0 m and maximum depth 7.0 m.
(iii) Chinglepet fort moat
This 2.4 ha moat is very different from the Vellore moat in being very shallow (average depth 1.0 m, maximum depth 3.0 m) and in not being as highly polluted as the latter. It is fed to a small extent by a large irrigation tank known as ‘Kolovai lake.’
(iv) Karpurachettikulam (K.C. Kulam)
This is a deep 0.6 ha pond in Chinglepet town used for bathing cattle, washing clothes, etc. This is filled by storm water. The maximum depth is 6 m and average depth 2 m; the shallow areas are very small.
(v) Odathurai tank
This is a large irrigation tank of about 73 ha (180 acres) extent which shrinks to about 40 ha(100 acres) in summer (mean area: 50 ha, 125 acres). This is fed by a seepage stream of Bhavani canal. The bottom is almost flat with very few steep slopes. The maximum depth is about 6.5 m while the average depth is about 1.5 m. There is continuous inflow and outflow for about eight months a year since the water is taken out for irrigation of crops. Thus, this is in fact a small impoundment and plankton blooms are not evident.
Data on physical and chemical conditions are given in Table I. All the five ponds described here are tropical ponds with temperatures not lower than 25.0°C and reaching 36.2°C. Variations in temperature were not wide and thermal stratification was only rarely noted (only in the deep Ayyankulam).
A very characteristic feature of these ponds is the absence of free carbon dioxide in the organically enriched ponds, Vellore fort moat, Chinglepet fort moat, Ayyankulam, and in the reservoir-type pond Odathurai. But Karpurachettikulam was different in that free carbon dioxide was present at times and in high concentrations of 22 mg/l. Very high phenolphathalein alkalinity was noted in Vellore moat(128.0 ppm); in Chinglepet moat it was 80.0 ppm, Ayyankulam 50.0 ppm and in Odathurai tank 61.0 ppm. Methyl orange alkalinity was very high in Karpurachettikulam (285 to 722 ppm) and fairly high in Chinglepet moat (164 to 370 ppm) and Odathurai (180 to 484 ppm) and Ayyankulam (100 to 125 ppm). But though mostly high, at times methyl orange alkalinity was absent in Vellore moat at periods when hydroxide alkalinity ensued (pH> 9.6).
The pH value was always very high in Vellore moat (8.3 to 9.6) and fairly high in Chinglepet moat (7.5 to 9.25), Ayyankulam (7.3 to 9.1) and Odathurai (8.5 to 8.7). In K.C. Kulam it was low on some occasions (6.9).
Oxygen disappears from the bottom in Vellore moat and pronounced depletion occurs in the lower layers of Ayyankulam. Even in the very shallow Chinglepet moat, the oxygen content is low even in surface waters in the early forenoon (2.0 mg/l). Similar condition was observed also in K.C. Kulam. However in the large Odathurai tank, the dissolved oxygen was fairly normal, though not as high as in the other four ponds.
The chloride content is very high in Vellore moat, 118 to 715 ppm. In K.C. Kulam it was 190 to 242 ppm, Ayyankulam 190 to 242 ppm, and only slightly less in Chinglepet moat (76 to 124 ppm). It was low in Odathurai tank, 16.5 to 93.0 ppm.
Vellore moat had the highest water hardness, 222 to 656 ppm. Ayyankulam and K.C. Kulam waters also had hardness exceeding 200 ppm. Chinglepet moat has also water of high hardness, 113 to 180 ppm. The electrical conductivity of Vellore moat and Ayyankulam are very high (over 1000 μ.mho) and that of K.C.Kulam equally high, 800 to 1,900 μ.mho. Chinglepet moat (475 to 1,150) and Odathurai tank (400 to 525) had moderately high conductivities.
Very high phosphate content throughout the year is a feature of Vellore moat (0.16 to 4.0 ppm) and K.C.Kulam (0.24 to 1.2 ppm). Soluble inorganic phosphate was not noticed in Chinglepet moat and Ayyankulam at any time. In Odathurai tank, phosphate was occasionally present in small amounts (0.1 ppm). Silicate was very high in Ayyankulam but moderate in other ponds. Nitrate was not detected in any of these ponds at any time.
This was moderately high, over 30 mg/l as Ca, in all the ponds.
There is variation in the occurrence of plankton groups from pond to pond and also in the same pond seasonally.
(i) Vellore moat
This has a predominantly blue-green bloom, especially of Microcystis aeruginosa, often to the exclusion of others. A high population of zooplankters was also noticeable here.
(ii) Chinglepet moat
Here, blue-green algae are important at times but not dominant. They occurred along with members of Chlorophyceae in May 1965. The number of genera noticed at times is larger than in other ponds. In August 1964, diatoms were dominant. In November 1964 no blue-greens were noticed but only green algae. Abundant zooplankters were present when blue-green algae were noted.
(iii) Ayyankulam
This pond was dominated by blue-green algae, the most frequent and numerous ones being Oscillatoria and Microcystis species.
(iv) K.C. Kulam
In this pond, blue greens, Chlorophyceae and colonial flagellates (green algae) were present. Zooplankters were fairly numerous. This pond had a very rich bottom fauna of gastropods, chironomid larvae, oligochaetes, annelids, etc.
(v) Odathurai tank
This was poor in plankton, being a flowing water for the major part of the year. Zooplankters were insignificant. Phytoplankton consisted mainly of diatoms. Gastropods were abundant and a few chironomids and annelids were also present.
In the deeper ponds, such as Vellore moat and Ayyankulam where shallows were limited, bottom fauna is also limited. Even in the shallow Chinglepet moat the bottom fauna was very insignificant. Details of the plankton are given in Table V.
Productivity measurements are given in Table III. Photosynthetic oxygen production is very high in Vellore moat but a low level is also noticed sometimes (range 1.9 to 42.3 g O2/m2/day). Ayyankulam shows a steady high production throughout the year (ranging from 16.01 to 29.34 g O2/m2/day). Chinglepet moat (10.5 to 18.5) and K.C. Kulam (10.0 to 26.1 g O2/m2/day) also have high production. Odathurai has the least oxygen production of the five (1.75 to 6.83 g O2/m2/day), but for an impounded water this is normal. Productivity as inferred from oxygen and carbon dioxide changes is high in Chinglepet moat, Vellore moat, Ayyankulam and to a lesser extent in K.C. Kulam and least in Odathurai tank.
We have under study here four types of waters: (i) two fort moats, (ii) one temple tank, (iii) one village pond, and (iv) a small irrigation impoundment. The two fort moats differ greatly from one another. Chinglepet moat is very shallow and is filled by fresh water from a large rainfed tank and is not heavily polluted by sewage or sullage, in contrast to the Vellore fort moat which is deep and very heavily polluted. The higher temperature of Chinglepet moat is due to its shallowness. Both waters invariably had phenolphthalein alkalinity (free carbon dioxide being absent), but on occasions hydroxide alkalinity occurs in Vellore moat due to very high photosynthesis and consequent utilization of all bicarbonate. In Vellore moat phenolphthalein alkalinity as high as 128 ppm (CaCO3) occurs, while the maximum in Chinglepet moat is 80.0 ppm (Table II). This was lowest in Odathurai tank. The pH value is influenced by changes in carbon dioxide, CO3" and HCO'3. Both the diurnal and depth variations of pH indicate the high metabolic levels of the waters and high productivity. When photosynthesis is high, the pH increases to a high level by afternoon and, as in the case of Vellore moat, even hydroxide alkalinity is produced. Likewise a vertical gradient in pH also indicates high metabolic activity. Due to a high rate of photosynthesis and the concurrent utilization of free carbon dioxide, HCO3', etc. from the euphotic zone, the pH increases (CaCO3 being precipitated). While due to lack of penetration of sunlight and the consequent inadequacy or absence of photosynthesis no such utilization of free carbon dioxide or HCO3' occurs in the bottom waters. Further, due to catabolic activity (mainly bacterial), free carbon dioxide increases in the bottom and by attacking the precipitated CO3" increases the HCO3' also. Thus, in productive waters there is a gradient of free carbon dioxide, CO"3 and HCO'3. In highly buffered waters, however, the pH gradient may not be very marked. The very slight variation in the pH of Odathurai water is striking. The changes in alkalinity and pH are very low in Odathurai tank indicating a lower rate of photosynthesis. Thus, maximum increase in dissolved oxygen was only 2.0 mg/l. In the other four waters the changes were very great (Table II). The pH value of K.C. Kulam did not rise above 8.6 but touched a low level of 6.9. Ayyankulam and Chinglepet moat recorded the upper value of 9.1.
All the ponds except Chinglepet moat are very hard waters - invariably over 200 ppm CaCO3 - but the former is only moderately hard, not as high as the other four (113 to 180 ppm). The chloride value was also lower in this moat, in contrast to the others, again an indication of milder pollution. The calcium content was high in all the ponds but here again that of Chinglepet moat was slightly lower than that of the others. Electrical conductivity, an index of total dissolved salts, was highest in Vellore moat, next highest in Ayyankulam and K.C. Kulam. It was almost similar in Chinglepet moat, and in Odathurai tank this was also fairly high.
Dissolved oxygen data also reveal the productivity of the waters. Hutchinson's statement (1957) that a skillful limnologist can probably learn more about the nature of a lake from a series of O2 determinations than from any other kind of chemical data is quite valid for our work. There is a diurnal increase in dissolved oxygen with very low values before day-break and peak value of supersaturation in the afternoon; a wide fluctuation is characteristic of productive biotopes. Also a vertical steep gradient with supersaturation or high saturation at the surface and complete disappearance, or deficit at the bottom, is a characteristic of such waters. High photosynthesis in the euphotic zone results in supersaturation of oxygen in that zone; this zone is severely restricted to a thin layer less than 3 m because of the blanketing effect (Prowse, 1963) of the overgrowth of plankton, sometimes a permanent bloom. The falling plankton, bottom organisms and bacteria all deplete the poor oxygen resources of the bottom layer. Thus we see the spectacle of oxygen supersaturated at the surface and H2S predominant on the bottom (just below 5 m) in Vellore moat.
The deficit was less severe in the other ponds. In Odathurai tank, which is shallow and also has continuous inflow and outflow refreshing the water, the oxygen deficit is not severe. In larger and deeper reservoirs like Amaravathy, oxygen depletion in the hypolimnion waters has been noticed (Sreenivasan, 1965).
Community respiration or the oxygen consumption in the dark bottle (B.O.D.), also indicates the comparative productive capacity of waters. It is very high in Vellore moat and Ayyankulam, the two most productive waters; it is slightly less in Chinglepet moat and K.C. Kulam, and least in Odathurai tank. Elsewhere (Sreenivasan, 1964b) it has been shown that in oligotrophic lakes there is practically no community respiration. In large sheets of water subject to strong wind action, for example, Odathurai tank, the oxygen change may not show much variation because, if supersaturated, oxygen may escape into the air, while, if undersaturated, oxygen will diffuse into the water by the agitation caused by winds. But in static bodies of water, oxygen changes during day reflect the productivity changes in phenolphthalein and methyl orange alkalinity in open waters. The maximum rate of oxygen production in the euphotic zone measured by the bottle method also reflects the productivity of the biotope (Sreenivasan, 1964a,c).
Overabundance of plankton alone does not increase productivity. The ‘self shading effect’ of a blanket of algae (Prowse, 1963) restricts the production to only the top 1 m or so in Vellore moat. Also the quality of plankton determines the efficiency of photosynthesis. Excess production of carbon dioxide in K.C. Kulam shows that it is either receiving excess organic matter or is digesting more organic matter than is synthesized by photosynthesis.
As far as fish yield is concerned, it can be seen from Table IV that the output (average of seven or eight years) from Vellore fort moat, Ayyankulam and K.C. Kulam are almost the same. The yield from Chinglepet fort moat was a little lower, but this is because the pond was too shallow (average depth 1.0 m) and the “lebensraum” was very restricted for fishes. The yield from the large ‘tank’ (an impoundment) Odathurai was lower, less than 100 kg/ha, but this was indicated by the lower rate of primary production and much lower rates of metabolism of the water and the poor plankton. Though chemical parameters of this tank are similar to those for the other four bodies of water, the wide diurnal fluctuations typical of highly productive waters were lacking.
It is thus possible to determine the fish production potential of biotopes by studying primary production as well as the diurnal and depth variations in certain chemical factors, reflecting the metabolism of these waters.
Grateful thanks are due to Dr. G.A. Prowse, Director, Tropical Fish Culture Research Institute, Malacca, for going through the manuscript and offering valuable suggestions.
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Hutchinson, C.E., 1957 A treatise on limnology. Vol.1. London, John Wiley, 1009 p.
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Sarig, S., 1961 Fisheries and fish culture in Israel in 1960. Bamidgeh, 13(¾):61–76
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Table I
Physical and chemical conditions of the five biotopes
| Temperature °C | Free carbon dioxide ppm | Alkalinity (ppm) CaCO3 | pH | Dissolved oxygen mg/l | Chloride | ||
| Phenolphthalein | methyl orange | ||||||
| Vellore fort moat | 26.0–31.8 | 0.0 | 2.0–128.0 | 0.0–64.0 | 8.3–9.6 | 0.0–27.3 | 118–715 |
| Chinglepet fort moat | 26.8–33.0 | 0.0 | 1.0–80.0 | 164–370 | 7.5–9.25 | 2.0–16.6 | 76–124 |
| Ayyankulam | 25.0–34.2 | 0.0-0.0 | 7.5–50.0 | 100–225 | 7.3–9.1 | 0.6–19.2 | 93–280 |
| K.C.Kulam | 28.8–36.2 | 0.0–22.0 | 0.0–66.0 | 285–722 | 6.9–8.8 | 1.2–16.6 | 190–242 |
| Odathurai tank | 27.2–33.5 | 0.0 | 23.7–61.0 | 180–480 | 8.1–8.7 | 5.0–9.6 | 16.5–9.30 |
| Hardness CaCO3 ppm | Electrical conductivity μ.mho | Phosphate mg/l | Silicate mg/l | Calcium mg/l | Oxygen absorbed | |
| Vellore fort moat | 222–656 | 975–2805 | 0.16–4.0 | 2.5–60.0 | 44.8–56.3 | 5.4–17.1 |
| Chinglepet fort moat | 113–180 | 475–1150 | Nil-Tr | 1.2–3.5 | 15.5–37.8 | 0.8–4.4 |
| Ayyankulam | 264–314 | 1075–1370 | 0.0 | 50–66.0 | 43.6–52.1 | 4.7–17.0 |
| K.C.Kulam | 170–245 | 800–1900 | 0.24–1.2 | 1.2–6.4 | 33.0–64.4 | 4.7–8.6 |
| Odathurai tank | 126–284 | 400–525 | 0.10-0.0 | 2.2–4.2 | 41.6–26.0 | 8.2 |
Table II
Variations in certain chemical conditions
| A. Diurnal variations (surface) | ||||||
| Free carbon dioxide ppm | Alkalinity (ppm) CaCO3 | Dissolved oxygen mg/l | pH | |||
| Phenolphthalein alkalinity | Methyl orange alkalinity | |||||
| Chinglepet fort moat | (a) | .. | 32.0–88.0 | 158-59 | 2.4–17.6 | 8.0–9.25 |
| (b) | .. | 44.0–70.0 | 360-293 | 3.6–10.8 | 8.1–8.6 | |
| K.C.Kulam | (a) | 14-12 | 27.8–68.5 | 444-187 | 3.2–15.6 | 8.2–8.8 |
| (b) | .. | 0.0–19.0 | 390-385 | 5.6–9.8 | 7.9–8.0 | |
| Vellore fort moat | (a) | .. | 50.0–128.0 | 280-198 | 13.6–27.0 | 8.2–8.8 |
| (b) | .. | 67.5-67.5 | 225-225 | 8.2–10.8 | 8.9–9.0 | |
| Ayyankulam | (a) | .. | 30.0–50.0 | 165-118 | 5.4–18.4 | 7.9–8.8 |
| (b) | .. | 17.0–22.0 | 150-142 | 5.6–13.4 | 8.6–8.9 | |
| Odathurai tank | (a) | .. | 61.0–72.0 | 205-178 | 8.2–10.6 | 8.5–8.6 |
| (b) | .. | 45.0-45.0 | 411-402 | 5.0–5.7 | 8.7–8.7 | |
| B. Depth variations | ||||||
| Free carbon dioxide ppm | Alkalinity (ppm) CaCO3 | Dissolved oxygen mg/l | pH | |||
| Phenolphthalein alkalinity | Methyl orange alkalinity | |||||
| Chinglepet fort moat | (a) | 0.0–6.2 | 30.0–4.4 | 360–370 | 2.6-1.8 | 7.8-7.5 |
| (b) | .. | 4.0-4.0 | 302–304 | 2.0-2.0 | 7.9-7.9 | |
| K.C.Kulam | (a) | 14.0–22.0 | 24.0–28.0 | 444–468 | 3.2-1.2 | 7.1-6.9 |
| (b) | .. | 12.0-12.0 | 390-390 | 2.6-1.2 | 8.2-8.2 | |
| Vellore fort moat | (a) | 0.0–45.0 | 27.5–67.5 | 225–366 | 13.6-4.8 | 9.2-8.7 |
| (b) | .. | 32.5–35.0 | 280–290 | 3.4-3.2 | 8.9-8.8 | |
| Ayyankulam | (a) | 0.0–5.0 | 0.0–17.0 | 150–225 | 19.0-1.4 | 8.9-8.8 |
| (b) | .. | 10.0–15.0 | 165–170 | 5.4-4.6 | 7.9-7.6 | |
| Odathurai tank | (a) | .. | 23.0–33.0 | 205–224 | 7.4-6.4 | 8.1-7.9 |
| (b) | .. | .. | .. | .. | .. | |
Table III
Productivity measurements of the five biotopes
| Primary production | Productivity rates μ mol/l/hr | Secchi disc visibility cm | Community respiration mg/l/h/O2 | ||||
| Gross g O2/m2/day | Maximum rate mg/m3/day | By oxygen change method | By changes in alkalinity | From maximum rates in bottle experiment | |||
| Vellore fort moat | 1.9–42.3 | 6.67–45.15 | 11.0–125.0 | 8.0–250.0 | 3.50–123.0 | 21–80 | 0.13–0.92 |
| Chinglepet fort moat | 10.5–18.5 | 30.0–34.4 | 30.0–55.0 | 78–176 | 78.1–90.0 | 31–50 | 0.17–0.45 |
| Ayyankulam | 16.0–29.3 | 19.73–37.07 | 37.0–100.0 | 16–183 | 52.0–96.0 | 30–60 | 0.15–1.30 |
| K.C.Kulam | 10.0–26.06 | 14.4–57.6 | 22.0–50.0 | 12.0–230.0 | 38.0–150.0 | 35–68 | 0.20–0.34 |
| Odathurai tank | 3.15–6.83 | 2.6–20.7 | 3.0–7.8 | 0.0–51.0 | 2.6–30.0 | 15.0–71* | 0.03–0.2 |
Table IV
Fish yield in the five biotopes
(Total in kg - figures in parentheses kg/ha)
| Year | Vellore fort moat | Chinglepet fort moat | K.C.Kulam | Ayyankulam | Odathurai tank |
| 1 | 2 | 3 | 4 | 5 | 6 |
| 1957–58 | 10,470 (2,169) | No data | 217(362) | 2,278(1,627) | 2,842(57) |
| 1958–59 | 10,740 (2,239) | 659(275) | 323(538) | 1,121(801) | 3,777(72) |
| 1959–60 | 7,678 (1,600) | 2,414(1,007) | 719(1,198) | 2,204(1,574) | 3,485(70) |
| 1960–61 | 6,288 (1,310) | 2,153(900) | 771(1,285) | 3,687(2,633) | 6,363(127) |
| 1961–62 | 4,178 (870) | 2,311(963) | 1,017(1,695) | 1,733(1,245) | 4,465(89) |
| 1962–63 | 4,926 (1,027) | 2,506(1,044) | 1,205(2,008) | 1,901(1,358) | 5,231(105) |
| 1963–64 | 2,260 (471) | 2,912(1,240) | 1,469(2,448) | 2,013(1,438) | 5,388(108) |
| 1964–65 | No data | 3,270(1,363) | 1,849(3,081) | No data | 3,008(60) |
Table V
Plankton of the five biotopes
| Vellore fort moat | Ayyankulam | Chinglepet fort moat | K.C.Kulam | Odathurai tank |
| 5–200 μl/l | 5–30 μl/l | 100-30 μl/l | 100–300 μl/l | 1 μl/l |
| Microcystis (permanent bloom) | Oscillatoria | Spirulina | Miscrocystis | Oscillatoria |
| Anabaena | Microcystis | Nostoc | Nodularis | Microcystis |
| Nostoc | Merismopedia | Oscillatoria | Nostoc | Navicula |
| Scenedesmus | Lyngbya | Microcoleus | Merismopedia | Cyclotella |
| Ankistrodesmus | Scenedesmus | Tetrapedia | Tetrapedia | Gyrosigma |
| Ulothrix | Peridinium | Merismopedia | Oscillatoria | Ankistrodesmus |
| Aphanizomenon | Euglena | Microcystis | Selenastrum | Fragilaria |
| Ulothrix | Rhaphidiopsis | Maugeotia | Scenedesmus | Pediastrum |
| Navicula | Navicula | Stephanodiscus | Crucigenia | Spirulina |
| Cyclotella | Nitzschia | Navicula | Pediastrum | Spirogyra |
| Noduloria | Ankistrodesmus | Nitzschia | Tetraspora | Tetrapedia |
| Phormidium | Volvox | Cyclotella | Ophiocytium | Euglena |
| Selenstrum | Ulothrix | Amphora | Euglena | Ceratium |
| Melosira | Volvox | Navicula | ||
| Scenedesmus | Pandorina | Scenedesmus | ||
| Cocconeis | Closterium | Microcoleus | ||
| Staurastrum | Chlorella | |||
| Selenastrum | Cosmarium | |||
| Peridinium | Navicula | |||
| Oocystis | Phacus | |||
| Closterium | Oocystis | |||
| Tribonema | Staurastrum | |||
| Pediastrum | Amphora | |||
| Pandorina | ||||
| Eudorina | ||||
| Pleodorina | ||||
| Pinnularia | ||||
| Diatoma | ||||
| Synedra | ||||
| Cosmarium | ||||
| Ceratium | ||||
| Euglena | ||||
| Nodularia |
