D. S. JOHNSON
Department of Zoology
University of Singapore
Republic of Singapore
Only one species of fresh-water prawn, Cryphiops (Macrobrachium) rosenbergii (de Man), is at present exploited on any considerable scale in Malaysia. A species of potential value is Cryphiops (Macrobrachium) lanchesteri (de Man), despite its relatively small size. Favourable features include: the large numbers in which it may occur; its ability to reproduce in standing fresh waters; its pronounced eurytopy; and its apparently vegetarian habits. Given suitable environmental conditions, it would be a suitable species for pond culture.
BIOLOGIE DE CERTAINES CREVETTES D'EAU DOUCE SUSCEPTIBLES DE PRESENTER UN INTERET COMMERCIAL, NOTAMMENT LA CREVETTE DES RIZIERES Cryphiops (Macrobrachium) lanchesteri (de Man)
Actuellement, une seule espèce de crevette d'eau douce, Cryphiops (Macrobrachium) rosenbergii (de Man) est exploitée de manière assez étendue en Malaisie. Une autre espèce qui pourrait se révéler intéressante malgré sa petite taille est Cryphiops (Macrobrachium) lanchesteri (de Man). Les caractéristiques favorables de cette espèce comprennent notamment: son abondance relative; son aptitude à se reproduire en eau douce stagnante; son eurytopie prononcée; enfin, ses habitudes apparemment végétariennes. Dans des conditions de milieu appropriées cette espèce devrait convenir à l'élevage en étang.
BIOLOGIA DE LANGOSTINOS DE AGUA DULCE POTENCIALMENTE VALIOSOS CON ESPECIAL REFERENCIA AL LANGOSTINO Cryphiops (Macrobrachium) lanchesteri (de Man)
Sólo una especie de langostino de agua dulce, Cryphiops (Macrobrachium) rosenbergii (de Man), se explota actualmente en escala algo considerable en Malasia. A pesar de su tamaño relativamente pequeño, una especie de valor potencial es Cryphiops (Macrobrachium) lanchesteri (de Man). Sus características favorables incluyen: las grandes cantidades en que existen; capacidad para reproducirse en aguas dulces inmóviles; su destacada euritopía; y sus aparentes costumbres vegetarianas. En condiciones ambientales favorables sería una especie adecuada para su cultivo en estanques.
In Malaya1 prawns form an important element in the fauna of most fresh-water habitats though they are absent from many isolated ponds, some streams and rivers in high mountains, and moderately to highly polluted waters. Their abundance, their role in the ecology of fresh-water habitats and their high protein content give them considerable potential importance.
Lanchester (1901) reported a few species of prawns collected by the Skeat expedition. He also collected several species at Singapore in 1899 but made no report on these. They have been examined by Johnson (1962a) together with specimens collected by Flower. Roux (1935; 1936) deals with two species of fresh-water prawns. In recent years the author has been carrying out a program of taxonomical and distributional studies. The results have been published in a series of papers (Johnson, 1960a, 1960b, 1961, 1962a, 1962b, 1964). The relation between distribution of several species and various physical and chemical factors is discussed by Johnson (1967b). Two recent papers (Johnson 1966 and Johnson (in press)) attempt to assess their potential value as food organisms.
The only Malaysian species which is at present exploited on any considerable scale is the udang galah, Cryphiops (Macrobrachium) rosenbergii (de Man). This species, the largest of the oriental fresh-water prawns, is popular in Malaysia, though not in Singapore, and available supplies are scarcely sufficient to meet the demand. The Malaysian Fisheries Department instituted a program of research, which is chiefly concerned with developmental requirements and other problems involved in large-scale culture of this prawn (Ling, 1962; Ling and Merican, 1961). The larvae can now be reared on a large scale in low salinity water and the young prawns used for stocking isolated fresh-water ponds. The carnivorous and cannibalistic tendencies of this species, however, limit its usefulness for pond culture.
One justification, though by no means the only one, for pursuing general research on Malaysian fresh-water prawns, is the possibility that one or more hitherto unexploited or under-exploited species may prove to possess potential economic value. The present paper is an attempt to summarize some of this research carried out with limited facilities, as a part-time study. It does not purport to be a final report, but is intended rather as a pointer to possible further research.
1 To be considered for the purpose of this paper as comprising western Malaysia and the Republic of Singapore
Amongst the fresh-water prawns considered of economic importance by Holthuis and Rosa (1965), they list several species as occurring in the area 433 (Malaysia, Singapore, Cocos and Keeling Islands). Johnson (in press) has given detailed comments on these. Caridina gracilirostris de Man is specifically indicated as being cultured in area 433, whereas it is not exploited at all. Of the species which they list, the only one that is currently exploited in Malaya on any noteworthy scale is Cryphiops (Macrobrachium) rosenbergii. Atya spinipes Newport is the object of a very small-scale subsistence fishery in a few areas.
It is possible that the small atyid prawns, such as Caridina gracilirostris, C. propinqua de Man, and C. tonkinensis Bouvier (not mentioned by Holthuis and Rosa), which occur in low salinity brackish waters, could form the basis of a culture fishery which might be especially attractive as a means of utilizing the productivity of waters which are now neglected. The more typically fresh-water species of this genus are distinctly local in Malaysia and sporadic in occurrence. In combination with their small size these distributional features suggest that they are not the most suitable species for exploitation in Malaysia, though pond culture of C. simoni peninsularis Kemp should be feasible.
The two commonest prawns of the tree country of southern Malaya are Cryphiops (Macrobrachium) geron (Holthuis) and C. (M). trompi (de Man) (not listed by Holthuis and Rosa (1965)). Both may be abundant in forest streams and rivers; both have excellent flavour. But the waters of their natural habitats tend to be unproductive so it is unlikely that either will ever be exploited on a large scale.
Of the remaining species only two, C. (M). lanchesteri, the riceland prawn, and C. (M). sintangensis (de Man) appear to have potential economic value on present evidence. The former is more likely to prove important. Though it is somewhat the smaller it is more widespread, often more abundant where it occurs, and more commonly found in ponds and ditches.
3.1 General considerations
C. (M). lanchesteri is a relatively small species but one which may make a considerable contribution to the biomass of the habitat in which it lives since it normally occurs in large numbers. A good swimmer, it is less strictly a bottom dweller than are many palaemonids. It has a light and somewhat compressed build and a relatively large abdomen and lives in fresh waters throughout its life cycle. The species appears to be indigenous to the swamps and ricelands of southeast Asia from where it appears to have penetrated south along the Malay peninsula. It has reached Singapore, probably through human agency, but has not yet been recorded in Indonesian waters.
Johnson (1964) mapped the Malaysian distribution of this species, but a number of new records have subsequently been added. It is now known to occur in the ricelands of central Trengannu and near Kuala Sedili Besar in eastern Johore. It probably occurs generally in riceland areas, and in the numerous fish ponds, slow rivers, streams, canals, many ditches, and in inundated disused mines.
In the Malaysian area ovigerous females of C. (M). lanchesteri may have an overall length of only 33 mm. Wild caught specimens seldom exceed 50 mm but the author obtained larger specimens from the research ponds of the Tropical Fish Culture Research Station at Batu Berendam, Malacca. The largest, a male, had an overall length of 62 mm. The large-sized males differ somewhat from the smaller individuals previously described and will necessitate a redescription of the species. In these ponds the pH, calcium content, and phosphate content of the water tend to be higher than in many natural habitats, and there is an abundant supply of digestible algae; but even where these conditions prevail in natural habitats such large individuals have not been obtained. A probable contributory factor is the rarity of efficient predatory fish which are excluded and eliminated in the ponds. It is quite likely that in uncontrolled habitats prawns do not survive long enough to attain the maximum size.
As stated earlier, C. (M). lanchesteri flourishes in standing and slowly flowing waters. Zoeae and post-larvae can sometimes be obtained from isolated pond habitats, and populations in such habitats appear to maintain themselves. It thus seems clear that breeding as well as growth may occur in stagnant water. Nonetheless populations can become established in streams with a moderate water flow if other conditions are favourable. The maximum flow which the author has recorded for such a habitat was 0.70m/sec.
Since C. (M). lanchesteri can live in shallow habitats it has to be able to withstand exposure to rather high temperatures for periods of several hours. The full range of temperatures from which the species has been collected is 25.5°C to 36.0°C, which corresponds to the temperature range of aquatic habitats in southern Malaya. Presumably it occurs at somewhat lower winter temperatures of countries to the north of Malaysia. It would be interesting to know the high temperature tolerance of the species in these countries since Malaysian specimens appear to be killed by slightly higher temperatures.
C. (M). lanchesteri does not appear to exhibit any behavioural response to increasing temperature. Thus during 1965 the author has observed that, at the Sembawang hot springs, Singapore, individual prawns continued to move undisturbed into water with temperature above 40°C though fishes turned back. The stretch of stream with temperatures between 40° and 45°C had the bottom littered with dead prawns. Similarly in open streams, in the middle of the day, the fish tend to congregate under bridges or in deep holes where the water temperature may be as much as 2°C below that of the rest of the stream; the prawns, by contrast, remain generally distributed.
Though no critical experiments have been carried out it appears from observations in hot springs that continued exposure to temperatures above 40°C is lethal to C. (M). lanchesteri. The upper safety margin is thus very small with the species flourishing in habitats in which the highest temperatures are only slightly below the lethal. However, throughout the Malaysian area temperatures of fresh waters seldom rise above 36°C and never above 37.5°C so that the hazard of high temperature death is more apparent than real. Nothing is known of lower temperature limits, but since the species occurs in more seasonal climates than in Malaysia it is unlikely that any such limitation by low temperature will be operative in the Malaysian area.
Water oxygen determinations from 45 habitats of C. (M). lanchesteri yielded a saturation range from 1 to 148 percent. About 13.3 percent of the habitats had less than 25 percent oxygen saturation. All readings were taken during daylight at least 3 h after sunrise. The present observations indicate that C. (M). lanchesteri is more tolerant to low oxygen than are other Malaysian prawns. It is the only species which has been collected from a habitat with less than 10 percent oxygen saturation. It should be noted, however, that it has never been collected from any habitat with oxygen so low as to be undetectable by the ordinary Winkler method.
Like other prawns, C. (M). lanchesteri appears to be unable to withstand any marked degree of organic pollution though it is not clear just which factors are deleterious. Low oxygen content might be operative in some habitats but the species is absent even where the oxygen content is apparently high. Intolerance to high concentrations of ammonia is another possible limiting factor. No records from habitats with ammonia concentrations greater than 4 ppm are available.
Though there is no precise information it is probable that this species is more tolerant to tin mine pollution than are most species, as evidenced by its common occurrence in mine pools and pools in tin tailings.
While abundant in fresh waters C. (M). lanchesteri seldom occurs in estuarine waters. However, in the absence of experimental evidence one cannot rule out the possibility that it is euryhaline, being excluded from more saline waters by biotic factors. Whatever the reason, this inability to penetrate high salinity waters is important in restricting its natural distribution, and has probably prevented it from spreading to Indonesia. Though it is present on Penang and Singapore islands, it has not been found on other small islands in the area.
It has been stated earlier that all developmental stages of this prawn can thrive in fully fresh-water habitats. It occurs in a reservoir near Malacca where the salinity (Hutchinson, 1957) is only 5.91 ppm, and it thrives in riceland streams in the same area with salinities between 10.0 and 20.0 ppm.
Tolerance to chloride ion concentration is related to the general problem of salinity tolerance. In the ionically well balanced waters of the Sembawang hot springs the chloride ion concentration was 9.504 mEq/l 2, corresponding to a chlorinity of 0.97 parts per thousand. The species can survive in ionically well balanced waters when the chloride ion is as little as 0.036 mEq/l. C. (M). lanchesteri is absent in highly acid waters with a pronounced anion excess even if the chloride content is optimum, as observed in an irrigation canal at Klebang Besar near Malacca, which had a chloride concentration of 1.636 mEq/l, pH of 4.8 and an anion excess of 1.647 mEq/l.
The recorded limits for sodium concentration cover much the same range as those for chloride but with both lower and upper limits slightly higher, from 0.076 to 10.65 mEq/l. The ability of this and other Malaysian fresh-water prawns to survive in waters which are very poor in chloride and sodium is especially noteworthy.
3.8 Other chemical factors
C. (M). lanchesteri appears to be a eurytopic species capable of thriving under a wide variety of chemical conditions, though it is perhaps less adapted to acid waters than are such species as C. (M). trompii. It is most frequently found in waters with pH between 6.0 and 7.0 and there are no records from waters with pH below 4.9. Johnson (1967b) gives 7.6 as the upper limit but it has since been found that the species can survive in habitats where the daytime pH may exceed 9.0. The rarity of such records merely reflects the rarity of freshwaters with pH exceeding 7.5 in southern Malaya.
The records for alkalinity give a similar picture to those for pH, the mean value of 46 records being 0.460 mEq/l. There are few records from localities with alkalinity below 0.150 mEq/l and the lowest alkalinity from which the species has been recorded is 0.080 mEq/l. Thus though C. (M). lanchesteri occurs in soft waters it does not extend into the extremely soft waters common in southern Malaya. It does, however, occur in habitats with alkalinities up to 2.80 mEq/l. It is absent in waters in which there is a considerable absolute anion excess.
Chloride ion concentration has already been considered under section 3.7. The limited records for sulphate ion concentrations are mostly from waters which are poor in sulphate with concentrations ranging from about 0.001 to 0.268 mEq/l. The exception was at the Sembawang hot springs where the sulphate concentration is as high as 1.58 mEq/l. Thus C. (M). lanchesteri can tolerate moderately high sulphate concentrations in waters which are ionically well balanced. Its absence from acid sulphate waters may well be due to the marked anion excess and consequent low pH of these waters. The ability to survive in habitats where there are only traces of sulphate ion is especially noteworthy in view of the widespread occurrence of such waters in many tropical areas.
Almost all southern Malayan waters are poor in calcium (Johnson, 1967 a). The author has recorded C. (M). lanchesteri from waters with calcium content ranging from 0.000 to 0.287 mEq/l. It is fairly certain that there are localities in northern and central Malaya in which C. (M). lanchesteri occurs in waters of higher calcium concentrations. According to the classification of Ohle (1934) as modified by Williams (1964) all these habitats are poor in calcium. However it is as well to note that many C. (M). lanchesteri habitats have biota of a type which in other countries would indicate calcium-rich waters, even though chemical determinations show the waters to be calcium-poor. Thus in Lake Chenderoh in Perak, snails and bivalves are very abundant, yet, according to the analysis kindly provided by J. W. Wood, Chief Chemist of the Perak River Hydro-Electric Power Company Ltd., the calcium content in August 1964 was only 0.160 mEq/l. The capacity of this prawn (and such other species as C. (M). trompii) to survive in habitats with calcium concentrations of less than 1 part in 100,000,000 is remarkable in view of the physiological requirements of decapod crustaceans. Concentrations of magnesium appear to be parallel to those of calcium, but the species has not been found in habitats devoid of magnesium. It is also absent from the magnesium rich gelam-type waters of the Malacca area, with pronounced anion excess and very low pH. Sodium contents of the habitats have already been discussed in section 3.7. In most Malayan habitats sodium is found to be in excess of calcium whatever the absolute concentrations. Recorded potassium concentrations of waters where the species occurs range from 0.005 to 0.707 mEq/l.
At present there is little precise information on the food of this and most other Malaysian fresh-water prawns. Observations on food are especially difficult for palaemonid prawns because of their small size, the delicate structure of the proventriculus and the extremely finely comminuted nature of its contents that makes identification often impossible. Observations on gut contents must, therefore, be supplemented by observations on feeding under natural conditions.
Most of the larger fresh-water palaemonids appear to be to some extent carnivorous as is C. (M). rosenbergii but the carnivorous tendencies are less marked or absent in many smaller species. There is no evidence of predation or cannibalism in C. (M). lanchesteri. It does not feed on higher plants nor on large pieces of vegetable detritus. The few observations on its feeding, and on the contents of its proventriculus (algal remains and chlorophyll), suggest that it is an algal feeder.
It will be clear from the above that our knowledge of the biology of Malaysian fresh-water prawns is still inadequate. We know fairly well which species occur and something of the conditions under which they live. From such data we can presume the possible limiting factors. For most species we know very little about food and reproduction and nothing of important physiological features, longevity, and growth rates. There is hardly any information on the standing stock of any species.
Nonetheless what is known is sufficient to suggest possible productive lines of investigation. Little attempt has been made to exploit these fresh-water prawns with the exception of C. (M). rosenbergii. That species is valuable because of its large size and good flavour but it has several disadvantages. The early larval stages require brackish water; the adults are at least partially carnivorous and also cannibalistic. Only a few of the remaining species occur in productive waters in sufficient abundance to suggest that they could form the basis of a possible prawn fishery or pond culture industry. Of these the riceland prawn, C. (M). lanchesteri, appears the most promising.
C. (M). lanchesteri can flourish and breed under pond conditions. It is eurytopic with respect to most environmental factors and seems to be well adapted to the soft waters found in most parts of Malaysia. It is not cannibalistic, at least under normal conditions, and appears to be vegetarian. Though it is of rather small size, it is larger than many other prawns which are of economic importance. Moreover it occurs in large numbers and can attain a larger size under specially favourable conditions. All of these features indicate its suitability for pond culture provided that adequate demand and adequate collecting and marketing facilities are available.
In ponds C. (M). lanchesteri competes with herbivorous food fish. It is not known how far this depresses fish production, but Dr Chen Foo-Yan of the Tropical Fish Culture Research Institute, Malacca, informs (personal communication) that there is some evidence that the presence of large numbers of prawns is associated with lower yields of algal feeding fish, while invertebrate feeders may benefit. It may well prove very difficult for a fish farmer to exclude C. (M). lanchesteri from his ponds. In ponds stocked with algae-feeding fish the presence of the prawn will adversely affect fish production. Exploitation of the prawn, if economically feasible, would turn an unavoidable loss into a definite gain.
In drawing attention to a species which appears to be potentially valuable, it is suggested that further research be undertaken not merely on its biology but also on relevant economic and sociological factors before it can conclusively be decided what use, if any, can be made of this riceland prawn.
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