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Freshwater prawn farming. A manual for the culture of macrobrachium rosenbergii
92
have been made both in Israel and S. Carolina, U.S.A., but unfortunately only the latter are reviewed in the book. Three chapters on lobster (Homarus americanus) conclude section 2 and clearly demonstrate the problems yet to be solved before lobsters can be reliably produced let alone cultured commercially. From a research perspective, the chapter on maturation and spawning of lobster lucidly describes the “state of the art” but those on hatchery and grow-out technique are not as detailed as they could be. Diseases are the subject of an authoritative and comprehensive section 3 and emphasis is placed on the role of careful husbandry and water management in disease prevention and control. There are few indications of the proportion of production costs likely to be attributable to disease and disease control in commercial operations. The final section entitled “crustacean nutrition” contains compact reviews of the nutritional requirements of M. rosenbergii and lobsters and the commercial feeding practices used in M. rosenbergii farms in Hawaii. There is no corresponding chapter on penaeid nutrition and one can only assume that such an omission was unintentional. The overall emphasis of this book is on the technology needed for controlled and reproducible cultures and this makes the volume important reading for commercial operators who wish to integrate such techniques within the framework of existing operations. I feel this handbook will also be of great value to researchers, extension workers, and all who wish to grow prawns and lobsters for some years to come. With due regard for its few shortcomings, this volume will also provide a particularly convenient source of information for those new to the field as well as those who do not have adequate access to the literature. J.F. WICKINS
Airlie, Betws-yn-Rhos, A bergele, Clwyd LL22 SAT (Great Britain)
FRESHWATER
PRAWN
FARMING
Freshwater Prawn Farming. A manual for the culture of Macrobrachium rosenbergii. M.B. New and S. Singholka. FAO Fish. Tech. Pap. 225. FAO,
Rome, 1982.
116 pp., US$ 4.90, ISBN 92-5-101265-2.
New and Singholka’s well presented practical manual on giant freshwater prawn farming is valuable because it tells prospective prawn farmers what to expect and how to cope with most aspects of prawn farming. Too often aquaculture investors, excited by the intrinsic attraction of growing aquatic animals, rush into site selection, pond excavation, stocking, etc. without
93
clear insight into the basic problems involved. If it does nothing more, this manual provides base lines in those areas. The authors’ plan for the manual’s layout is interesting. They say, (p. 1) they were going to write an abbreviated “cookbook” because “there is so much art as well as science in successful prawn farming”. This approach did not prove feasible and so they adopted the narrational form. It seems successful. Certainly the answers to most queries running through my brain during reading were found fairly close by in the text. Of 100 or so species of Macrobrachium distributed around the tropical and subtropical zones of the world, M. rosenbergii is the most commonly farmed. Following its 1965-66 transfer out of Malaysia into Hawaii, it is now farmed significantly in Honduras, Mauritius, Taiwan and Thailand. Farms are currently being established in Costa Rica, Indonesia, Israel, Malaysia, Mexico, the Philippines and Zimbabwe. M. rosenbergii is a decapod crustacean with a hard shell. It belongs to a group loosely called “shrimps” or “prawns” and it grows to a body length of approximately 8-12 cm (23/--5% in) and a total weight of approximately 60-96 g. Both sexes have pincers longer than the body length, particularly the males who, as a result, usually have much heavier weights than females. During development Macrobrachium passes through egg, larva, postlarva and adult stages. Males mate with females when the latter have just moulted their shells and are still soft. The sperm are stored alive within the female for up to 3 weeks. Virgin females produce 5000 to 20 000 eggs, which are fertilised by the sperm as they pass out. Older females produce 80 000 to 100 000 eggs. All eggs are incubated by the females for about 20 days at 28°C (range 18-23 days) and then released as larvae. The latter must move into brackish water (12%,) within a few days of hatching to survive. They moult frequently, eat continuously and metamorphose into postlarvae 2-3 weeks after hatching. For food the authors recommend brine shrimp nauplii (BSN) or prepared food (PF), but other preparations are also available. Postlarvae are 7 mm long, look like young adults, and can be gradually transferred into freshwater for growth to maturity. Suitable foods include raw animal and vegetable material, food mixtures cooked on the pond bank and commercial feedstuff mixtures. Two different growout methods are used. In “batch culture” the pond is stocked, grown and then totally harvested. In “continuous culture” the ponds are usually stocked annually and harvesting commences after 5-7 months and continues each month. The ponds are never drained. In both cases, human-pulled seine nets are favoured. Protagonists of the second method, which is favoured by many Hawaiian and now some Thailand farmers, claim outputs of 2500-4000 kg/ha per year. The manual deals in considerable detail with giant prawn farming, mainly based on Thailand systems. Only major items can be highlighted here. Regarding (1) hatchery site requirements, the items considered essential were reliable power supply, all-weather access, maximum of 16 h transport to furthest customer, professional, technical and managerial skills, optimum
94
28-30°C climate and good access to fresh and seawater. Regarding (2) hatchery facilities, the optimum larval rearing tank was considered to be rectangular, concrete, 14 m* with water level at 70 cm holding 10 m3 of water, dimensions 1 m deep X 2 m wide X 7 m long. Holding and mixing tanks, similar but 1 m deep X 7 m wide X 10 m long, are also required, as well as an oil-free air blower (and spare) and water measurements and purification methods. For (3) hatchery operation, good methods for obtaining and looking after eggs are provided, as well as the working requirements for salinity, temperature, dissolved oxygen, general water quality management, light and hygiene. (4) Feeding is outlined here (and detailed in Appendices 3, 4, 7) followed by (5) larval growth rate, harvesting, holding and transport and (6) problems and al terna tive hatchery techniques. The important section (7) rearing site requirements follows and discusses markets, water, power, topography and soil, access, fry supply, feeds, sympathetic authorities (a nice term that) and labour. (8) Farm facilities is next, presenting good advice on pond construction. Rectangular ponds 30 m wide are most suitable for seining and if 200 m long will be 0.6 ha, a fairly suitable size. Larger ponds are wider and often drained for harvesting. This well illustrated section shows how to build suitable ponds in detail, including walls, screens, filters, sluices, etc. The vital section (9) feeding follows, While perhaps 200-300 kg/ha per year may be obtained from natural pond productivity, successful farming must involve extra feeding. This can incorporate rice, tapioca and trash fish. Compounded foods, though dearer (US$400 to well over US$ 1000 per ton), are usually more efficient to use. Feeding rate is determined by placing food in shallow water at the pond edge and seeing how much is consumed overnight. If none is left the rate is increased until satisfactory. It is important for the farmer to keep notes so that he can work out how each pond behaves under a certain management regime (and they vary). The last section (10) harvesting is well described and illustrated and also outlines alternative rearing techniques. For further details the titles of 72 specially selected scientific papers are included as well as 39 pages of appendices giving all sorts of details on water filtration, pumps, shrimp food procedures, hatching procedures, prepared foods, larval stage identification, stock estimates, pond food formulae, seine net design and a glossary of terms and conversions. It was not the authors’ purpose to compare the economy of Thailand prawn farming with that of other countries. However, Shang (1982) has made an interesting comparison of Thailand and Hawaii in this regard. Hawaiian productivity was twice that of Thailand due to an intensive type of operation, but Thailand production costs were less than half those of Hawaii because of comparatively inexpensive inputs. However, farm prices for prawns were relatively high for both countries: $7.3O/kg for Thailand and $S.SO/kg for Hawaii. Low production costs and high farm prawn prices for Thailand resulted in a relatively high profit.
95
One hopes that in future editions of this manual a section on the economics of Thailand, Hawaii and other emerging prawn-farming countries (Taiwan, Mauritius, Puerto Rico), will be included giving, as far as is practical, an analysis of prawn farming profit, break-even farm price, break-even production level and rate of return. BAUGHAN WISELY Brackishwater Fish Culture Research Station, Port Stephens, c/o Post Office, Salamander Bay,N.S. W. (Australia)
REFERENCE Shang, Y.C., 1982. Freshwater prawn (Macrobrachium rosenbergii) production in Hawaii: practices and economics. Sea Grant Miscellaneous Report UNIHI-SEAGRANT-MR-8107 Aquaculture Development Program, Department of Land and Natural Resources, State of Hawaii, 36 pp.
MOUTH-BROODING
TILAPIAS
Tilapiine Fishes of the Genera Sarotherodon, Oreochromis and Danakilia. Ethelwynn Trewavas. British Museum (Natural History), London, 1983. 583 pp., 188 fig., 119 tables, $50.00, ISBN 0-565-00878-l. The monograph on the mouth-brooding species of the Tilapiini announced by Trewavas (1982) was published in December 1983. It is a milestone in the taxonomy of the tilapias, as well as being the final document summarizing 50 years of active research, mainly devoted to tilapias, by its main investigator. The 70-odd tilapia species can be divided into mouth-brooders and substrate-brooders. The first brood eggs and young in the mouth, the second attach eggs to the substrate, and the parents guard the eggs, the hatchlings and larvae. The species of interest for fish-farming all belong to the mouthbrooders. Trewavas has separated off this category into three distinct genera, Sarotherodon (9 species), Oreochromis (31 species) and Danakilia (1 species). The other category, the substrate-brooders, has kept the name Tilapia, as the first tilapia described belonged to this group (T. sparrmanii). Those who wish to refer to the group as a whole, and colloquially, may use the word tilapia (pl. tilapias) as a common name, just like e.g. carp, salmon and trout. The book by Trewavas is a record of the distribution of the genera and species of the mouth-brooding tilapias before interference by man. To quote the authoress, “it may also help those interested to identify the species now in their waters, but the fishes themselves have sometimes failed to distinguish their new neighbours and have interbred with them”.
have been made both in Israel and S. Carolina, U.S.A., but unfortunately only the latter are reviewed in the book. Three chapters on lobster (Homarus americanus) conclude section 2 and clearly demonstrate the problems yet to be solved before lobsters can be reliably produced let alone cultured commercially. From a research perspective, the chapter on maturation and spawning of lobster lucidly describes the “state of the art” but those on hatchery and grow-out technique are not as detailed as they could be. Diseases are the subject of an authoritative and comprehensive section 3 and emphasis is placed on the role of careful husbandry and water management in disease prevention and control. There are few indications of the proportion of production costs likely to be attributable to disease and disease control in commercial operations. The final section entitled “crustacean nutrition” contains compact reviews of the nutritional requirements of M. rosenbergii and lobsters and the commercial feeding practices used in M. rosenbergii farms in Hawaii. There is no corresponding chapter on penaeid nutrition and one can only assume that such an omission was unintentional. The overall emphasis of this book is on the technology needed for controlled and reproducible cultures and this makes the volume important reading for commercial operators who wish to integrate such techniques within the framework of existing operations. I feel this handbook will also be of great value to researchers, extension workers, and all who wish to grow prawns and lobsters for some years to come. With due regard for its few shortcomings, this volume will also provide a particularly convenient source of information for those new to the field as well as those who do not have adequate access to the literature. J.F. WICKINS
Airlie, Betws-yn-Rhos, A bergele, Clwyd LL22 SAT (Great Britain)
FRESHWATER
PRAWN
FARMING
Freshwater Prawn Farming. A manual for the culture of Macrobrachium rosenbergii. M.B. New and S. Singholka. FAO Fish. Tech. Pap. 225. FAO,
Rome, 1982.
116 pp., US$ 4.90, ISBN 92-5-101265-2.
New and Singholka’s well presented practical manual on giant freshwater prawn farming is valuable because it tells prospective prawn farmers what to expect and how to cope with most aspects of prawn farming. Too often aquaculture investors, excited by the intrinsic attraction of growing aquatic animals, rush into site selection, pond excavation, stocking, etc. without
93
clear insight into the basic problems involved. If it does nothing more, this manual provides base lines in those areas. The authors’ plan for the manual’s layout is interesting. They say, (p. 1) they were going to write an abbreviated “cookbook” because “there is so much art as well as science in successful prawn farming”. This approach did not prove feasible and so they adopted the narrational form. It seems successful. Certainly the answers to most queries running through my brain during reading were found fairly close by in the text. Of 100 or so species of Macrobrachium distributed around the tropical and subtropical zones of the world, M. rosenbergii is the most commonly farmed. Following its 1965-66 transfer out of Malaysia into Hawaii, it is now farmed significantly in Honduras, Mauritius, Taiwan and Thailand. Farms are currently being established in Costa Rica, Indonesia, Israel, Malaysia, Mexico, the Philippines and Zimbabwe. M. rosenbergii is a decapod crustacean with a hard shell. It belongs to a group loosely called “shrimps” or “prawns” and it grows to a body length of approximately 8-12 cm (23/--5% in) and a total weight of approximately 60-96 g. Both sexes have pincers longer than the body length, particularly the males who, as a result, usually have much heavier weights than females. During development Macrobrachium passes through egg, larva, postlarva and adult stages. Males mate with females when the latter have just moulted their shells and are still soft. The sperm are stored alive within the female for up to 3 weeks. Virgin females produce 5000 to 20 000 eggs, which are fertilised by the sperm as they pass out. Older females produce 80 000 to 100 000 eggs. All eggs are incubated by the females for about 20 days at 28°C (range 18-23 days) and then released as larvae. The latter must move into brackish water (12%,) within a few days of hatching to survive. They moult frequently, eat continuously and metamorphose into postlarvae 2-3 weeks after hatching. For food the authors recommend brine shrimp nauplii (BSN) or prepared food (PF), but other preparations are also available. Postlarvae are 7 mm long, look like young adults, and can be gradually transferred into freshwater for growth to maturity. Suitable foods include raw animal and vegetable material, food mixtures cooked on the pond bank and commercial feedstuff mixtures. Two different growout methods are used. In “batch culture” the pond is stocked, grown and then totally harvested. In “continuous culture” the ponds are usually stocked annually and harvesting commences after 5-7 months and continues each month. The ponds are never drained. In both cases, human-pulled seine nets are favoured. Protagonists of the second method, which is favoured by many Hawaiian and now some Thailand farmers, claim outputs of 2500-4000 kg/ha per year. The manual deals in considerable detail with giant prawn farming, mainly based on Thailand systems. Only major items can be highlighted here. Regarding (1) hatchery site requirements, the items considered essential were reliable power supply, all-weather access, maximum of 16 h transport to furthest customer, professional, technical and managerial skills, optimum
94
28-30°C climate and good access to fresh and seawater. Regarding (2) hatchery facilities, the optimum larval rearing tank was considered to be rectangular, concrete, 14 m* with water level at 70 cm holding 10 m3 of water, dimensions 1 m deep X 2 m wide X 7 m long. Holding and mixing tanks, similar but 1 m deep X 7 m wide X 10 m long, are also required, as well as an oil-free air blower (and spare) and water measurements and purification methods. For (3) hatchery operation, good methods for obtaining and looking after eggs are provided, as well as the working requirements for salinity, temperature, dissolved oxygen, general water quality management, light and hygiene. (4) Feeding is outlined here (and detailed in Appendices 3, 4, 7) followed by (5) larval growth rate, harvesting, holding and transport and (6) problems and al terna tive hatchery techniques. The important section (7) rearing site requirements follows and discusses markets, water, power, topography and soil, access, fry supply, feeds, sympathetic authorities (a nice term that) and labour. (8) Farm facilities is next, presenting good advice on pond construction. Rectangular ponds 30 m wide are most suitable for seining and if 200 m long will be 0.6 ha, a fairly suitable size. Larger ponds are wider and often drained for harvesting. This well illustrated section shows how to build suitable ponds in detail, including walls, screens, filters, sluices, etc. The vital section (9) feeding follows, While perhaps 200-300 kg/ha per year may be obtained from natural pond productivity, successful farming must involve extra feeding. This can incorporate rice, tapioca and trash fish. Compounded foods, though dearer (US$400 to well over US$ 1000 per ton), are usually more efficient to use. Feeding rate is determined by placing food in shallow water at the pond edge and seeing how much is consumed overnight. If none is left the rate is increased until satisfactory. It is important for the farmer to keep notes so that he can work out how each pond behaves under a certain management regime (and they vary). The last section (10) harvesting is well described and illustrated and also outlines alternative rearing techniques. For further details the titles of 72 specially selected scientific papers are included as well as 39 pages of appendices giving all sorts of details on water filtration, pumps, shrimp food procedures, hatching procedures, prepared foods, larval stage identification, stock estimates, pond food formulae, seine net design and a glossary of terms and conversions. It was not the authors’ purpose to compare the economy of Thailand prawn farming with that of other countries. However, Shang (1982) has made an interesting comparison of Thailand and Hawaii in this regard. Hawaiian productivity was twice that of Thailand due to an intensive type of operation, but Thailand production costs were less than half those of Hawaii because of comparatively inexpensive inputs. However, farm prices for prawns were relatively high for both countries: $7.3O/kg for Thailand and $S.SO/kg for Hawaii. Low production costs and high farm prawn prices for Thailand resulted in a relatively high profit.
95
One hopes that in future editions of this manual a section on the economics of Thailand, Hawaii and other emerging prawn-farming countries (Taiwan, Mauritius, Puerto Rico), will be included giving, as far as is practical, an analysis of prawn farming profit, break-even farm price, break-even production level and rate of return. BAUGHAN WISELY Brackishwater Fish Culture Research Station, Port Stephens, c/o Post Office, Salamander Bay,N.S. W. (Australia)
REFERENCE Shang, Y.C., 1982. Freshwater prawn (Macrobrachium rosenbergii) production in Hawaii: practices and economics. Sea Grant Miscellaneous Report UNIHI-SEAGRANT-MR-8107 Aquaculture Development Program, Department of Land and Natural Resources, State of Hawaii, 36 pp.
MOUTH-BROODING
TILAPIAS
Tilapiine Fishes of the Genera Sarotherodon, Oreochromis and Danakilia. Ethelwynn Trewavas. British Museum (Natural History), London, 1983. 583 pp., 188 fig., 119 tables, $50.00, ISBN 0-565-00878-l. The monograph on the mouth-brooding species of the Tilapiini announced by Trewavas (1982) was published in December 1983. It is a milestone in the taxonomy of the tilapias, as well as being the final document summarizing 50 years of active research, mainly devoted to tilapias, by its main investigator. The 70-odd tilapia species can be divided into mouth-brooders and substrate-brooders. The first brood eggs and young in the mouth, the second attach eggs to the substrate, and the parents guard the eggs, the hatchlings and larvae. The species of interest for fish-farming all belong to the mouthbrooders. Trewavas has separated off this category into three distinct genera, Sarotherodon (9 species), Oreochromis (31 species) and Danakilia (1 species). The other category, the substrate-brooders, has kept the name Tilapia, as the first tilapia described belonged to this group (T. sparrmanii). Those who wish to refer to the group as a whole, and colloquially, may use the word tilapia (pl. tilapias) as a common name, just like e.g. carp, salmon and trout. The book by Trewavas is a record of the distribution of the genera and species of the mouth-brooding tilapias before interference by man. To quote the authoress, “it may also help those interested to identify the species now in their waters, but the fishes themselves have sometimes failed to distinguish their new neighbours and have interbred with them”.