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Hatching trials with eggs of the armoured catfish Hoplosternum littorale (Hancock)
Aquaculture 198 Ž2001. 123–127 www.elsevier.nlrlocateraqua-online
Hatching trials with eggs of the armoured catfish Hoplosternum littorale žHancock/ I.W. Ramnarine ) Department of Life Sciences, UniÕersity of the West Indies, St. Augustine, Trinidad and Tobago Received 15 March 2000; accepted 13 December 2000
Abstract The armoured catfish Hoplosternum littorale ŽHancock. is commercially cultured in Trinidad and Tobago, Guyana and Suriname. In some culture systems, fingerlings are collected from the wild, but more commonly the fingerlings are hatchery produced. Hatching success is a key problem. In initial hatching trials with low hatching success, the culture water was found to contain high populations of the bacterium Aeromonas hydrophila and the fungus Saprolegnia sp. In subsequent trials, the egg masses were treated with antibiotics and anti-fungal agents. While the anti-fungal treatment of intact egg masses had little apparent effect on hatching success, the antibiotic treatment resulted in an increase from 52.2% to 60.5%. When egg masses were broken into smaller pieces and treated with antibiotics and anti-fungal agents, hatching success increased from 50.0% to 81.8%. This suggests that treatment of the egg masses with antibiotics and anti-fungal agents is more effective with smaller egg masses. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Hoplosternum littorale; Eggs; Incubation
1. Introduction The armoured catfish Hoplosternum littorale ŽHancock, 1828. is native to northern South America east of the Andes. The fish has been suggested as a potential culture species ŽPrice, 1955; Boujard et al., 1988; Ramnarine, 1989. and is now commercially cultured in Trinidad, Guyana and Suriname. The cascadu, as the fish is known in
)
Tel.: q1-868-645-3232r9 ext. 3093; fax: q1-868-663-9686. E-mail address: Indar – [email protected] ŽI.W. Ramnarine..
0044-8486r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 4 - 8 4 8 6 Ž 0 1 . 0 0 5 0 4 - X
124
I.W. Ramnariner Aquaculture 198 (2001) 123–127
Trinidad, fetches a price of US$8rkg and there are local and foreign ethnic markets for the fish. It satisfies most of the criteria of Webber and Riordan Ž1976. in selecting culture species. The fish reproduces in the rainy season and builds a floating, domeshaped nest of dead vegetative matter. A mass of adhesive eggs is laid in the dark underside of the nest within a foamy layer, and the male cascadu tends to the developing embryos and guards the nest. The number of eggs in the mass ranges from 2000 to 22000 ŽSingh, 1978.. Several studies have been done with the cascadu. A technology for induction of spawning has been developed ŽRamnarine, 1995a., the embryological and larval development have been described ŽRamnarine, 1994a, 1996. and the optimal protein requirement has been determined ŽRamnarine, 1995b.. Field trials using practical diets have been conducted ŽRamnarine, 1994b.. However, incubation of the eggs remains problematic. In previous hatching trials with low and variable hatching success, the incubation water was tested for microbial agents and was found to contain high levels of the bacterium Aeromonas hydrophila and the fungus Saprolegnia sp. This suggested that poor hatching success might be due to microbial infection of the eggs through these agents. The purpose of this study was to determine whether microbial infection was one of the main causes of low hatching success.
2. Materials and methods Egg masses were obtained by inducing adult fish to spawn, by lowering the conductivity of the water using the technique described by Ramnarine Ž1995a.. In the first experiment, egg masses were carefully removed from the nests and treated with the antibiotic terramycin and the anti-fungal agent methylene blue as described in Table 1. In the second experiment, the egg masses were carefully broken apart to about one-tenth the original size Ž12.3 " 2.6 g ws.d.x. using gloved hands. The broken egg masses were treated as in experiment 1 with methylene blue andror terramycin as outlined in Table 1. In both experiments and for each treatment there were six replicates. The egg masses were supported on epoxy-coated 1-cm2 wire troughs lined on the outside with mosquito netting. The egg masses were incubated in darkened aquaria Ž60 = 30 = 30 cm. in treated or untreated water ŽTable 1. at a depth of 15 cm at a constant temperature of 288C, using a static system. The water was sourced from the public supply and was sterilised and dechlorinated by passing through ultraviolet and activated carbon filters. The water was vigorously aerated with 30-cm-long ceramic diffusers. The mean incubation period of the eggs was 68.4 " 5.1 h Žs.d... The egg masses were observed during development. Upon hatching, aeration was reduced to a gentle flow and an estimate of hatching success was made. Initially, the number of eggs in a mass was estimated by counting those in a weighed sample, the weight of the total egg mass being known. Upon hatching, the number of larvae was estimated by sampling volumetrically and counting the number of larvae per sample, and then extrapolating to the total volume Žfor intact egg masses.. For broken egg masses,
I.W. Ramnariner Aquaculture 198 (2001) 123–127
125
Table 1 Hatching success of egg masses with various pre-treatments of terramycin and methylene blue Treatment
ŽA. Control ŽB. 5 min soak in 100 ppm methylene blue; incubated in untreated water ŽC. 5 min soak in 100 ppm methylene blue; incubated in water with 5 ppm methylene blue ŽD. 5 min soak in 100 ppm methylene blue and 100 ppm terramycin; incubated in water with 5 ppm methylene blue and 5 ppm terramycin
% Hatching success Experiment 1 Žintact egg masses.
Experiment 2 Žbroken egg masses.
52.2"17.0 49.7"8.9
50.0"12.6 78.0"5.5a
50.3"6.3
80.2"5.1a
60.5"7.6
81.8"5.0 a
Six egg masses of mean size 123"10.8 g were used in each treatment in experiment 1, and six broken egg masses of mean size 12.3"2.6 g in each treatment in experiment 2. All figures are mean"s.d. a Differs significantly Ž p- 0.01. from the same treatment in experiment 1 ŽStudent’s t-test..
the number of larvae was counted directly. All data generated were analysed using Tukey’s HSD test to compare differences between treatments in either experiments, and the Student’s t-test to compare differences in similar treatments between experiment 1 Žintact egg masses. and experiment 2 Žbroken egg masses..
3. Results The results of the experiments are presented in Table 1. With intact egg masses, hatching success ranged from 49.7% to 60.5%, but no significant difference was shown between treatments ŽTukey’s HSD test.. With broken egg masses on the other hand, egg masses treated with both antibiotics and anti-fungal agents had higher hatching success than untreated masses, ranging from 50.0% with untreated egg masses, to 78.0% with egg masses treated with methylene blue, to 80.2% with egg masses treated with methylene blue and incubated in water containing methylene blue, to 81.8% with egg masses treated with methylene blue and terramycin, and incubated in water containing these agents. The only significant difference Ž P - 0.05; Tukey’s HSD test. in hatching success was between the control and the last treatment ŽD.. When hatching success was compared between same-treatment intact and broken egg masses, in all cases except the control, there was an increase in hatching success. With the methylene blue treatment, hatching success increased from 49.7% to 78.0%; with the methylene blue treatment and incubation in water containing methylene blue, hatching success increased from 50.3% to 80.2%; with the methylene blue and terramycin treatment and incubation in water containing these agents, hatching success increased from 60.5% to 81.8%. In all cases except the control, these increases were highly significant Ž P - 0.01; t-test; Table 1..
126
I.W. Ramnariner Aquaculture 198 (2001) 123–127
4. Discussion The present results do not support the expectation ŽRamnarine, 1992. that with large, intact egg masses, the inclusion of antibiotics and anti-fungal agents in the incubation water will measurably improve hatching success. Other researchers have recommended treatment of fish egg masses with agents such as formalin, sodium chloride and hydrogen peroxide in order to reduce the incidence of fungal infections ŽFroelich and Engelhardt, 1996; Schreier et al., 1996; Barnes et al., 1997; Rach et al., 1997, 1998.. Barker et al. Ž1990. working on rainbow trout eggs have recommended treatment with oxolinic acid to reduce bacterial infections while Barnes et al. Ž1998. have shown that treatment of the eggs with hydrogen peroxide can control Saprolegnia infections. The current study, however, identified a new significant variable which impacted on hatching success. In all three experimentally treated treatments, small egg masses had markedly greater hatching success than large, intact masses. The antibiotic and anti-fungal treatments were evidently more effective with the broken egg masses. This suggested that penetration of the various treatments into the large, intact egg masses was not complete. There was also the possibility that aeration of the small egg masses was more efficient than with large, intact egg masses and this may also have had an impact on hatching success. It should be noted, however, that the almost identical hatching success of untreated intact and untreated broken egg masses appear to indicate that aeration was not a factor. It was therefore concluded that the small size of broken egg masses, which subsequently resulted in better penetration of antibiotics and anti-fungal agents, was the critical factor in improving egg hatching success. Another option that can be explored is the removal of egg matrices and stickiness of the eggs using chemical agents or clay, before treatment and incubation. This will be the subject of future research.
Acknowledgements The author thanks Dr C.K. Starr and three anonymous referees for reviewing the manuscript and for their helpful comments and suggestions.
References Barker, G.A., Smith, S.N., Bromage, N.R., 1990. Effect of oxolinic acid on bacteria flora and hatching success rate of rainbow trout, Oncorhynchus mykiss eggs. Aquaculture 91 Ž3–4., 205–222. Barnes, M.E., Cordes, R.J., Sayler, W.A., 1997. Use of formalim during incubation of eyed eggs of Inland Fall Chinook Salmon. Prog. Fish Cult. 59 Ž4., 303–306. Barnes, M.E., Ewing, D.E., Cordes, R.J., Young, G.L., 1998. Observations on hydrogen peroxide control of Saprolegnia spp. during Rainbow Trout egg incubation. Prog. Fish Cult. 60 Ž1., 67–70. Boujard, T., Lebail, P.Y., Planquette, P., 1988. Donnees sur quelques especes continentales de Guyane Francaise d’interet piscicole. Aquat. Liv. Resour. 1, 107–113. Froelich, S.L., Engelhardt, T., 1996. Comparative effects of formailn and salt treatments on hatch rates of Koi Carp eggs. Prog. Fish Cult. 58 Ž3., 209–211.
I.W. Ramnariner Aquaculture 198 (2001) 123–127
127
Hancock, J., 1828. Notes on some species of fishes and reptiles from Demerara presented to the Zoological Society by John Hancock. Zool. J. 4, 240–247. Price, J.L., 1955. A survey of the freshwater fishes of Trinidad. J. Agric. Soc. Trin. Tob., 863, Society Paper, 28 pp. Rach, J.J., Howe, G.E., Schreier, T.M., 1997. Safety of formalin treatments on warn and coolwater fish eggs. Aquaculture 149 Ž3–4., 183–191. Rach, J.J., Gaikowski, M.P., Howe, G.E., Schreier, T.M., 1998. Evaluation of the toxicity and efficacy of hydrogen peroxide treatments on eggs of warm and coolwater fishes. Aquaculture 165 Ž1–2., 11–25. Ramnarine, I.W., 1989. Cascadu Farming: a manual for the culture of Hoplosternum littorale. Ocasional Paper No 7, Dept. of Zoology, U.W.I., St Augustine, Trinidad, 34 pp. Ramnarine, I.W., 1992. Development, growth and nutritional requirements of the Casdadu Ž Hoplosternum littorale Hancock, 1828: Callichthyidae.. PhD Thesis, The University of the West Indies, 238 pp. Ramnarine, I.W., 1994a. Larval culture, development and growth of the cascadu Hoplosternum littorale. Aquaculture 126, 291–298. Ramnarine, I.W., 1994b. A field trial of the semi-intensive culture of the cascadu, Hoplosternum littorale. Trop. Agric. 71 Ž2., 135–138. Ramnarine, I.W., 1995a. Induction of nest building and spawning in Hoplosternum littorale. J. Fish Biol. 47, 555–557. Ramnarine, I.W., 1995b. The effects of varying dietary protein levels on growth, feed conversion, protein retention, and body composition in the armoured catfish, Hoplostermum littorale ŽHancock, 1828.. J. Aquat. Trop. 10, 159–165. Ramnarine, I.W., 1996. Early development of the cascadu, Hoplosternum littorale. J. Aquat. Trop. 11, 97–104. Schreier, T.M., Rach, J.J., Howe, G.E., 1996. Efficacy of formalin, hydrogen peroxide and sodium chloride on fungal-infected rainbow trout eggs. Aquaculture 140 Ž4., 323–331. Singh, T.B., 1978. The biology of the cascadu Hoplosternum littorale ŽHancock, 1828. with reference to its reproductive biology and population dynamics. PhD thesis, The University of the West Indies, 298 pp. Webber, H.H., Riordan, P.F., 1976. Criteria for candidate species for aquaculture. Aquaculture 7, 107–123.
Hatching trials with eggs of the armoured catfish Hoplosternum littorale žHancock/ I.W. Ramnarine ) Department of Life Sciences, UniÕersity of the West Indies, St. Augustine, Trinidad and Tobago Received 15 March 2000; accepted 13 December 2000
Abstract The armoured catfish Hoplosternum littorale ŽHancock. is commercially cultured in Trinidad and Tobago, Guyana and Suriname. In some culture systems, fingerlings are collected from the wild, but more commonly the fingerlings are hatchery produced. Hatching success is a key problem. In initial hatching trials with low hatching success, the culture water was found to contain high populations of the bacterium Aeromonas hydrophila and the fungus Saprolegnia sp. In subsequent trials, the egg masses were treated with antibiotics and anti-fungal agents. While the anti-fungal treatment of intact egg masses had little apparent effect on hatching success, the antibiotic treatment resulted in an increase from 52.2% to 60.5%. When egg masses were broken into smaller pieces and treated with antibiotics and anti-fungal agents, hatching success increased from 50.0% to 81.8%. This suggests that treatment of the egg masses with antibiotics and anti-fungal agents is more effective with smaller egg masses. q 2001 Elsevier Science B.V. All rights reserved. Keywords: Hoplosternum littorale; Eggs; Incubation
1. Introduction The armoured catfish Hoplosternum littorale ŽHancock, 1828. is native to northern South America east of the Andes. The fish has been suggested as a potential culture species ŽPrice, 1955; Boujard et al., 1988; Ramnarine, 1989. and is now commercially cultured in Trinidad, Guyana and Suriname. The cascadu, as the fish is known in
)
Tel.: q1-868-645-3232r9 ext. 3093; fax: q1-868-663-9686. E-mail address: Indar – [email protected] ŽI.W. Ramnarine..
0044-8486r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S 0 0 4 4 - 8 4 8 6 Ž 0 1 . 0 0 5 0 4 - X
124
I.W. Ramnariner Aquaculture 198 (2001) 123–127
Trinidad, fetches a price of US$8rkg and there are local and foreign ethnic markets for the fish. It satisfies most of the criteria of Webber and Riordan Ž1976. in selecting culture species. The fish reproduces in the rainy season and builds a floating, domeshaped nest of dead vegetative matter. A mass of adhesive eggs is laid in the dark underside of the nest within a foamy layer, and the male cascadu tends to the developing embryos and guards the nest. The number of eggs in the mass ranges from 2000 to 22000 ŽSingh, 1978.. Several studies have been done with the cascadu. A technology for induction of spawning has been developed ŽRamnarine, 1995a., the embryological and larval development have been described ŽRamnarine, 1994a, 1996. and the optimal protein requirement has been determined ŽRamnarine, 1995b.. Field trials using practical diets have been conducted ŽRamnarine, 1994b.. However, incubation of the eggs remains problematic. In previous hatching trials with low and variable hatching success, the incubation water was tested for microbial agents and was found to contain high levels of the bacterium Aeromonas hydrophila and the fungus Saprolegnia sp. This suggested that poor hatching success might be due to microbial infection of the eggs through these agents. The purpose of this study was to determine whether microbial infection was one of the main causes of low hatching success.
2. Materials and methods Egg masses were obtained by inducing adult fish to spawn, by lowering the conductivity of the water using the technique described by Ramnarine Ž1995a.. In the first experiment, egg masses were carefully removed from the nests and treated with the antibiotic terramycin and the anti-fungal agent methylene blue as described in Table 1. In the second experiment, the egg masses were carefully broken apart to about one-tenth the original size Ž12.3 " 2.6 g ws.d.x. using gloved hands. The broken egg masses were treated as in experiment 1 with methylene blue andror terramycin as outlined in Table 1. In both experiments and for each treatment there were six replicates. The egg masses were supported on epoxy-coated 1-cm2 wire troughs lined on the outside with mosquito netting. The egg masses were incubated in darkened aquaria Ž60 = 30 = 30 cm. in treated or untreated water ŽTable 1. at a depth of 15 cm at a constant temperature of 288C, using a static system. The water was sourced from the public supply and was sterilised and dechlorinated by passing through ultraviolet and activated carbon filters. The water was vigorously aerated with 30-cm-long ceramic diffusers. The mean incubation period of the eggs was 68.4 " 5.1 h Žs.d... The egg masses were observed during development. Upon hatching, aeration was reduced to a gentle flow and an estimate of hatching success was made. Initially, the number of eggs in a mass was estimated by counting those in a weighed sample, the weight of the total egg mass being known. Upon hatching, the number of larvae was estimated by sampling volumetrically and counting the number of larvae per sample, and then extrapolating to the total volume Žfor intact egg masses.. For broken egg masses,
I.W. Ramnariner Aquaculture 198 (2001) 123–127
125
Table 1 Hatching success of egg masses with various pre-treatments of terramycin and methylene blue Treatment
ŽA. Control ŽB. 5 min soak in 100 ppm methylene blue; incubated in untreated water ŽC. 5 min soak in 100 ppm methylene blue; incubated in water with 5 ppm methylene blue ŽD. 5 min soak in 100 ppm methylene blue and 100 ppm terramycin; incubated in water with 5 ppm methylene blue and 5 ppm terramycin
% Hatching success Experiment 1 Žintact egg masses.
Experiment 2 Žbroken egg masses.
52.2"17.0 49.7"8.9
50.0"12.6 78.0"5.5a
50.3"6.3
80.2"5.1a
60.5"7.6
81.8"5.0 a
Six egg masses of mean size 123"10.8 g were used in each treatment in experiment 1, and six broken egg masses of mean size 12.3"2.6 g in each treatment in experiment 2. All figures are mean"s.d. a Differs significantly Ž p- 0.01. from the same treatment in experiment 1 ŽStudent’s t-test..
the number of larvae was counted directly. All data generated were analysed using Tukey’s HSD test to compare differences between treatments in either experiments, and the Student’s t-test to compare differences in similar treatments between experiment 1 Žintact egg masses. and experiment 2 Žbroken egg masses..
3. Results The results of the experiments are presented in Table 1. With intact egg masses, hatching success ranged from 49.7% to 60.5%, but no significant difference was shown between treatments ŽTukey’s HSD test.. With broken egg masses on the other hand, egg masses treated with both antibiotics and anti-fungal agents had higher hatching success than untreated masses, ranging from 50.0% with untreated egg masses, to 78.0% with egg masses treated with methylene blue, to 80.2% with egg masses treated with methylene blue and incubated in water containing methylene blue, to 81.8% with egg masses treated with methylene blue and terramycin, and incubated in water containing these agents. The only significant difference Ž P - 0.05; Tukey’s HSD test. in hatching success was between the control and the last treatment ŽD.. When hatching success was compared between same-treatment intact and broken egg masses, in all cases except the control, there was an increase in hatching success. With the methylene blue treatment, hatching success increased from 49.7% to 78.0%; with the methylene blue treatment and incubation in water containing methylene blue, hatching success increased from 50.3% to 80.2%; with the methylene blue and terramycin treatment and incubation in water containing these agents, hatching success increased from 60.5% to 81.8%. In all cases except the control, these increases were highly significant Ž P - 0.01; t-test; Table 1..
126
I.W. Ramnariner Aquaculture 198 (2001) 123–127
4. Discussion The present results do not support the expectation ŽRamnarine, 1992. that with large, intact egg masses, the inclusion of antibiotics and anti-fungal agents in the incubation water will measurably improve hatching success. Other researchers have recommended treatment of fish egg masses with agents such as formalin, sodium chloride and hydrogen peroxide in order to reduce the incidence of fungal infections ŽFroelich and Engelhardt, 1996; Schreier et al., 1996; Barnes et al., 1997; Rach et al., 1997, 1998.. Barker et al. Ž1990. working on rainbow trout eggs have recommended treatment with oxolinic acid to reduce bacterial infections while Barnes et al. Ž1998. have shown that treatment of the eggs with hydrogen peroxide can control Saprolegnia infections. The current study, however, identified a new significant variable which impacted on hatching success. In all three experimentally treated treatments, small egg masses had markedly greater hatching success than large, intact masses. The antibiotic and anti-fungal treatments were evidently more effective with the broken egg masses. This suggested that penetration of the various treatments into the large, intact egg masses was not complete. There was also the possibility that aeration of the small egg masses was more efficient than with large, intact egg masses and this may also have had an impact on hatching success. It should be noted, however, that the almost identical hatching success of untreated intact and untreated broken egg masses appear to indicate that aeration was not a factor. It was therefore concluded that the small size of broken egg masses, which subsequently resulted in better penetration of antibiotics and anti-fungal agents, was the critical factor in improving egg hatching success. Another option that can be explored is the removal of egg matrices and stickiness of the eggs using chemical agents or clay, before treatment and incubation. This will be the subject of future research.
Acknowledgements The author thanks Dr C.K. Starr and three anonymous referees for reviewing the manuscript and for their helpful comments and suggestions.
References Barker, G.A., Smith, S.N., Bromage, N.R., 1990. Effect of oxolinic acid on bacteria flora and hatching success rate of rainbow trout, Oncorhynchus mykiss eggs. Aquaculture 91 Ž3–4., 205–222. Barnes, M.E., Cordes, R.J., Sayler, W.A., 1997. Use of formalim during incubation of eyed eggs of Inland Fall Chinook Salmon. Prog. Fish Cult. 59 Ž4., 303–306. Barnes, M.E., Ewing, D.E., Cordes, R.J., Young, G.L., 1998. Observations on hydrogen peroxide control of Saprolegnia spp. during Rainbow Trout egg incubation. Prog. Fish Cult. 60 Ž1., 67–70. Boujard, T., Lebail, P.Y., Planquette, P., 1988. Donnees sur quelques especes continentales de Guyane Francaise d’interet piscicole. Aquat. Liv. Resour. 1, 107–113. Froelich, S.L., Engelhardt, T., 1996. Comparative effects of formailn and salt treatments on hatch rates of Koi Carp eggs. Prog. Fish Cult. 58 Ž3., 209–211.
I.W. Ramnariner Aquaculture 198 (2001) 123–127
127
Hancock, J., 1828. Notes on some species of fishes and reptiles from Demerara presented to the Zoological Society by John Hancock. Zool. J. 4, 240–247. Price, J.L., 1955. A survey of the freshwater fishes of Trinidad. J. Agric. Soc. Trin. Tob., 863, Society Paper, 28 pp. Rach, J.J., Howe, G.E., Schreier, T.M., 1997. Safety of formalin treatments on warn and coolwater fish eggs. Aquaculture 149 Ž3–4., 183–191. Rach, J.J., Gaikowski, M.P., Howe, G.E., Schreier, T.M., 1998. Evaluation of the toxicity and efficacy of hydrogen peroxide treatments on eggs of warm and coolwater fishes. Aquaculture 165 Ž1–2., 11–25. Ramnarine, I.W., 1989. Cascadu Farming: a manual for the culture of Hoplosternum littorale. Ocasional Paper No 7, Dept. of Zoology, U.W.I., St Augustine, Trinidad, 34 pp. Ramnarine, I.W., 1992. Development, growth and nutritional requirements of the Casdadu Ž Hoplosternum littorale Hancock, 1828: Callichthyidae.. PhD Thesis, The University of the West Indies, 238 pp. Ramnarine, I.W., 1994a. Larval culture, development and growth of the cascadu Hoplosternum littorale. Aquaculture 126, 291–298. Ramnarine, I.W., 1994b. A field trial of the semi-intensive culture of the cascadu, Hoplosternum littorale. Trop. Agric. 71 Ž2., 135–138. Ramnarine, I.W., 1995a. Induction of nest building and spawning in Hoplosternum littorale. J. Fish Biol. 47, 555–557. Ramnarine, I.W., 1995b. The effects of varying dietary protein levels on growth, feed conversion, protein retention, and body composition in the armoured catfish, Hoplostermum littorale ŽHancock, 1828.. J. Aquat. Trop. 10, 159–165. Ramnarine, I.W., 1996. Early development of the cascadu, Hoplosternum littorale. J. Aquat. Trop. 11, 97–104. Schreier, T.M., Rach, J.J., Howe, G.E., 1996. Efficacy of formalin, hydrogen peroxide and sodium chloride on fungal-infected rainbow trout eggs. Aquaculture 140 Ž4., 323–331. Singh, T.B., 1978. The biology of the cascadu Hoplosternum littorale ŽHancock, 1828. with reference to its reproductive biology and population dynamics. PhD thesis, The University of the West Indies, 298 pp. Webber, H.H., Riordan, P.F., 1976. Criteria for candidate species for aquaculture. Aquaculture 7, 107–123.