Aquaculture Station Research Articles

Tilapia Fingerling Production in Honduras

ABSTRACT This study was supported by Aquaculture Collaborative Research Support Program (ACRSP) of the United States Agency for International Development (USAID) and conducted in Honduras by the Pan-American Agriculture School (PAS) from September 2003 and July 2004. The objective of the study was to evaluate tilapia fingerling production and examine the factors that influence the way farmers produce and distribute fingerlings and to provide recommendations to improve the quality and availability of fingerlings in Honduras. The study describes the socioeconomic characteristics of tilapia fingerling producers, their production techniques, as well as their needs for training and technical assistance in Honduras. Sixteen farmers were identified, visited, and interviewed. A sample from each farm of the 13 producing and distributing fingerlings was taken to the Aquaculture Station at the PAS to determine their count and evaluate their quality based on uniformity of size, color, and male gender. Seven of the fingerling farms are family owned, four are private companies, one is a cooperative, one is operated by a nonprofit organization (NGO), another is run by a university, and two by the government. In aggregate, they produce approximately 15.3 million fingerlings a year. Most (75%) of the fingerling producers interviewed also produce marketing size tilapia, produce other aquaculture species, and have other farm enterprises. Results show that fingerling sex reversal with hormone-treated feed is practiced by 13 of the 16 farmers. Tilapia fingerling producers have between 4 and 6 years of formal education and an average of 6.7 years of experience (range of 0–25 years). The results of the study suggest that a farmer's experience growing tilapia food fish is positively correlated to production of quality fingerlings. Analysis of the fingerling samples shows that there is variability on the quality of the fingerlings from one farm to another.

Evaluation of organic tilapia culture in periphyton-based ponds

The introduction of hard surfaces in the water column to induce the growth of biofilms and peri- phyton on these surfaces is a method used to increase natural productivity of the water body and food for cultured aquatic organisms. In periphyton-based systems in Africa and Asia, substrate introduction and consequent periphyton development positively affected water quality and pro- duction of the target species. In Israel, this technology is being evaluated in the culture of organ- ically produced tilapia. Among other restrictions imposed by organic standards, fish stocking densities must be low and only organic feeds and manures must be supplied. Organic pelleted feeds cost twice as much as regular aquaculture feeds. Since feed constitutes the major pro- duction expense, economic viability is hampered by using costly organic feeds. An experiment was performed at the Dor Aquaculture Station to explore methods of improving natural food pro- duction for tilapia and reducing added feeds. Submerged plastic surfaces equivalent to 40% of the pond surface area were immersed in polyculture ponds containing 85% hybrid tilapia (Oreochromis niloticus x O. aureus), together with a reduction of 40% of the amount of pelleted feed. The treatment improved nitrification and saved 40% of the feed costs, with only a 10% reduction in the tilapia growth rate and yield. These results indicate that periphyton-based aqua- culture is an appropriate technology for reducing production costs and allowing economically viable organic tilapia production.

Resistance to beta-lactam antibiotics in Aeromonas hydrophila isolated from rainbow trout (Oncorhynchus mykiss).

Bacterial infections caused by members of the genus Aeromonas, with a relatively high antibiotic resistance, are among the most common and troublesome diseases of fish raised in ponds with recirculation systems. In this study, carried out at an experimental aquaculture station in northern Portugal, 51 strains identified as belonging to the genus Aeromonas were isolated from 20 rainbow trout (Oncorhynchus mykiss) skin and kidney samples, as well as from raceway water samples. Macro- and microscopic examination of the fish tissues revealed lesions or cellular alterations in skin and kidney that seemed to correlate with the presence of those isolates. The sensitivity of all isolated strains to different groups of beta-lactam antibiotics (penicillins, cephalosporins, monobactams and carbapenems) was evaluated using the disc diffusion method. The highest rates of resistance were to amoxicillin, carbenicillin and ticarcillin. Unexpected resistance to imipenem, an antibiotic of clinical usage, was also detected, which suggests that resistance may have been transferred to the Aeromonas population from the environment.

Avaliação de níveis protéicos para a nutrição de juvenis de matrinxã (Brycon cephalus)

O matrinxã (Brycon cephalus - Gunther, 1869), é uma espécie de peixe nativa da bacia Amazônica que tem despertado grande interesse entre pesquisadores e piscicultores de todo o Brasil. A crescente demanda pelo cultivo desta espécie em ambiente controlado se deve, principalmente, à sua pronta adaptação ao cativeiro e à aceitação de alimentos artificiais, tanto de origem vegetal quanto animal, ao lado do seu elevado valor comercial. Contudo, para ser um empreendimento comercial bem sucedido, o alimento a ser fornecido a esta espécie deve atender a suas necessidades em proteína e permitir elevados ganhos de peso em períodos curtos. O experimento foi conduzido na estação de aqüicultura da Embrapa Amazônia Ocidental. Foram testados cinco níveis de proteína bruta (16, 19, 22, 25 e 28%) em dietas isocalóricas (EB = 390 kcal/100g) em um delineamento experimental inteiramente casualizado com três repetições para cada tratamento. Os resultados obtidos após 210 dias de estudo mostraram que a dieta contendo 28 % de proteína bruta promoveu o maior ganho de peso, melhor conversão alimentar e mais alto crescimento corporal entre os níveis testados, indicando que este nível protéico atendeu satisfatoriamente às necessidades de proteína para esta espécie, nas condições deste experimento.

Comparative Analysis of Pink Shrimp, Farfantepenaeus paulensis, and Pacific White Shrimp, Litopenaeus vannamei, Culture in Extreme Southern Brazil

ABSTRACT Culture potential of the native pink shrimp, Farfantepenaeus paulensis, and exotic Pacific white shrimp, Litopenaeus vannamei, was analyzed in extreme southern Brazil. The experiment was conducted at the Marine Aquaculture Station, University of Rio Grande, Rio Grande do Sul State. After nursery, pink shrimp (0.16 g) and Pacific white shrimp (0.17 g) juveniles were transferred to a 450 m2 earthen pond internally divided into six circular (21 m2 each) experimental pens. Pens were randomly assigned to a treatment (pink shrimp or Pacific white shrimp) and stocked at 15 shrimp/m2. Shrimp growth was monitored during 102 days in the summer. Feed was composed of a commercial diet and a fresh frozen mixture (fish and crustacean). After 30 days of culture, Pacific white shrimp showed significantly higher increases in mean weight, reaching at-harvest weight of 12.52 g compared to 11.17 g for pink shrimp. Water quality parameters presented optimal growing conditions for both species, except for lower temperatures (19°C) during the last two weeks of culture, which resulted in a drastic decrease in the growth rate of Pacific white shrimp. These results indicated a better tolerance for lower water temperatures on the part of shrimp. Although the lower temperatures resulted in a reduced number of cycles (1 or 2 per year), the estimated yield for pink shrimp (1,451 kg/ha) and Pacific white shrimp (1,790 kg/ha) suggested that the production per cycle in extreme southern Brazil is comparable to that in the other Brazilian States. Despite the more favorable results for Pacific white shrimp, the culture of pink shrimp is also recommended, but further studies are necessary to improve its growth performance under culture.

Genetic markers in Atlantic salmon, Salmo salar L., their potential for experimental studies of gene flow and adaptation

Abstract. In autumn 1992, a number of farmed and wild Atlantic salmon, Salmo salar L., spawners were screened for genetic variability in isoenzymes expressed in low-risk tissues. Samples of muscle and fin tissues were taken by biopsy shortly before spawning. In the Daleelv hatchery a male heterozygous for GPI-3*105 allele was crossed with four females homozygous for the common allele from Matre aquaculture station. In the River Hålva a wild male heterozygous for a GPI-1,2*160 allele was crossed with a female homozygous for the common allele. Another female from Matre aquaculture stations, heterozygous for the MDH-3,4*85 allele was crossed with a male homozygous for the common allele. Mortality was recorded during the egg and fry stages. The families were sampled four times during 1993, each individual was genotyped, and length and weight of the various genotypes recorded and compared. In all families the observed genotypic distributions were in close agreement with the expected Mendelian ratios, even in one family where the mortality was over 95%. There were no differences in performance between the two genotypes in any of the families. The inheritance of the observed variability was verified, and it is concluded that the detected alleles have a potential as genetic markers in experimental studies of gene flow and adaptation.

Available algal biomass in tropical brackish water artificial habitats

Experiments were conducted in February 1990 at the Layo Aquaculture Station located in Ebrié Lagoon, Ivory Coast, to find a reliable technique for the estimation of algal biomass and to understand the process that leads to a high tertiary productivity. Periphyton, growing on bamboo, was sampled at different settlement levels in an “acadja-enclos” at 200 m off the lagoon bank. “Acadja-enclos” is an extensive aquaculture system where Sarotherodon melanotheron (Cichlidae), a herbivorous fish, occurs mostly. Organic charge and periphytic concentrations (chl a, pheopigment, total pigments) were determined on each sample (from different locations). Specific microalgae composition and light intensity were also estimated. The periphytic community within the “acadja” was mainly composed of filamentous algae with Rhizoclonium (Kützing) (Chlorophyceae) as the major genus. Cyanobacteria and many species of the diatom Nitzschia comprised a high proportion of the epiphytes found. From a quantitative point of view, horizontal and vertical distributions of the biomass (mainly composed of algae) seemed to have been controlled by the availability of photosynthetic energy. However, the vertical heterogeneity was greater than the horizontal one. The maxima were situated close to the compensation depth. A high correlation was found between chlorophyll and organic matter ( r=+0.810); this reflects the high percentage of algal biomass. The total yield of the “acadja” (1250 m 2) was evaluated at 60 kg of dry matter; this value was five times higher than the algal biomass of the Ebrié Lagoon in the Layo area. Moreover, algal concentrations due to proliferation of periphytic species were eight times higher in the “acadja” than in the lagoon waters.

Effects of molluscivorous fish, water quality and pond management on the development of schistosomiasis vector snails in aquaculture ponds

One of the possible negative side-effects of aquaculture in tropical areas is the spread of water-related diseases, in particular schistosomiasis. Fish ponds can provide breeding sites for freshwater snails transmitting schistosomiasis (Berrie 1966). Scientific attention has long been concentrated on the use of molluscicides as the most effective means of snail and schistosomiasis control. However, molluscicides have limited use in aquaculture as they are expensive, hazardous to many other forms of aquatic life including fish, and have to be applied regularly because of the rapid recolonization by snails. This paper describes a study made on snail populations in an aquaculture station in northern Cameroon and their possible relation with water quality, pond management and cultured fish species. Together with production experiments, the development of snail populations in the fish ponds has been monitored during 2 years, and the biological control potentiality of two fish species has been tested. The experiments are part of a larger programme on the integrated control of schistosomiasis in the upper Benue Valley of northern Cameroon (Slootweg 1991). Three species of fish were used in the pond experiments. The tilapia, Oreochromis niloticus (L.), was used for production experiments under different nutritional regimes. To control the excessive reproduction by O. niloticus, the African catfish, Clarias gariepinus Burchell, was introduced in several experiments. C. gariepinus is also known to eat snails; based on stomach contents analyses of fish caught in an irrigation scheme in Sudan, Coates (1984) suggested using C. gariepinus in the control of schistosomiasis vector snails. As a third species, the East African cichlid fish Astatoreochromis alluaudi Pellegrin was introduced solely to test its capability to control molluscs (Slootweg 1989). In the literature A. alluaudi has often been recommended as a means of biological snail control, but the number of actual field trials is very limited. One experiment in Xenya showed a significant reduction in snail populations over a long period (McMahon 1960; McMahon, Highton & Marshall 1977), although contradictory evidence is given by recent research (Kat SL Kibberenge 1990). One successful experiment has been described from an aquaculture station near Yaounde in Cameroon (Bard & Mvogo 1963; Mvogo & Bard 1964), but has never been repeated afterwards.

First feeding of Atlantic salmon, Salmo salar L., under different photoperiods and light intensities

. First feeding fry of Atlantic salmon, Salmo salar L., were reared under four experimental light regimes from mid-June until mid-September. One group was reared under a simulated natural photoperiod 4 months out of phase, with initial daylength in mid-June corresponding to natural daylength in mid-February. Two groups were reared under continuous light of either low (27 lux) or high (1400 lux) intensity. The fourth group received a dual photoperiod combining a continuous, low intensity (27 lux) background illumination and a superimposed simulated natural photoperiod phase adjusted according to the natural photoperiod group. Growth rate and survival was higher during the first 3 weeks under continuous light or dual photoperiod than under the phase adjusted simulated natural photoperiod. This could partly be due to the restricted feeding time during the initial short daylength of the simulated natural photoperiod, and partly to a photostimulation of growth in groups reared under the continuous light regimes. Fish reared under a simulated natural photoperiod migrated vertically during the 24-hour cycle. The same behaviour was seen, though not as ctearly, in the fish reared under a dual photoperiod. Changes in light intensity appeared to be the primary releasing factor for the vertical migration observed. The fish reared under continuous light showed no diurnal vertical migration. Acknowledgments The authors would like to thank Dr Gunnar Naevdal and Dr Lars Petter Hansen for helpful suggestions and criticism of the manuscript. We also thank the staff at Matre Aquaculture Station for skilled assistance during the experiment. This study was financed by the Norwegian Fisheries Research Council (NFFR V.701.146).

Morphological and behavioural development of halibut, Hippoglossus hippoglossus (L.) larvae

Live yolk‐sac halibut, Hippoglossus hippoglossus (L.) larvae from rearing experiments at Austevoll Aquaculture Station, Norway, were examined from hatching to past first feeding for developmental morphology and behaviour. The findings include development of the respiratory and circulatory organs, eye pigmentation, mouth formation, organs of the digestive system and the process of yolk absorption, as well as swimming speed and activity levels.A stomodeum is not present at hatching although drinking is possible through a pair of branchial pits which gradually develop into the operculum and gill basket. The mouth normally opens slowly, the gape being restricted by a transverse septum until bones are formed. The amount of time spent swimming varies from less than 15% of the observation period during the first 2 weeks after hatching to between 70 and 100% around the seventh week after hatching, when individual differences become more apparent. Larvae generally react with a burst of swimming when two come into contact. Speed and duration of swimming seems to be correlated with development of eye pigment, heart size and fin formation. The yolk‐sac period is divided into four stages.

Suitability of brackish water tilapia species from the Ivory Coast for lagoon aquaculture. I – Reproduction

The main characteristics of the reproductive biology of Tilapia guineensis and Sarotherodon melanotheron have been studied in Ebrie lagoon (Ivory Coast), with a comparison between natural and cultured populations. In this lagoon, the two species breed throughout the year without interruption. However, seasonal variations in the intensity of the sexual activity have been observed and are more pronounced at the Layo aquaculture station, where the hydroclimate is more unstable than in other lagoon sectors studied. The proportion of mature individuals, the mean GSI, the relative fecundity and the spawning frequency are higher during the dry season than during the rainy season. In rearing enclosures, both species reach sexual maturity at a smaller size, and produce smaller but more numerous oocytes than in the wild. On the other hand, the relationship between the spawn weight and the female body weight are remarkably similar under both situations. For S. melanotheron, which is a male mouthbreeder, the number of brooded eggs or fry is positively related to the male body weight. In 2 m3 concrete tanks, the mean elapsed time between two successive spawnings is about 2 weeks for S. melanotheron and about 3 weeks for T. guineensis.

Monitoring Biological and Environmental Parameters in Aquaculture

The paper describes a system for monitoring the behaviour of salmon in culture in relation to environmental factors and different rearing conditions. The main objective of this work is to minimize the stress level of the fish by optimizing critical factors in crder to avoid disease and increase growth and fish quality.Two generations of salmon are investigated under normal rearing conditions in sea water at the Austevoll Aquaculture station. The distribution, behaviour and pysiological condition of the fish are studied by methods such as underwater biotelemetry, standard acoustic methods, underwater TV observations and blood sample analyses.Environmental factors such as temperature, salinity, oxygen, current, tide, meteorological data and light level are continuously monitored. Several of these parameters are measured by different types of sensors for calibration and testing purposes.The sensors are interfaced to a HP-1000 computer. Special process monitoring and control software gives trend and historical analyses of stored data.

Modifications et transformations des ecosystemes sedimentaires par des elevages piscicoles en lagune Ebrie (Cote d'Ivoire)

This paper presents the results of a comparative study on three types of sediments sampled within the new aquaculture structures tested in the Ebrie lagoon (Ivory Coast): enclosure and enclosure cages. These structures are situated in shallow brackish water (between 0 and 5‰ salinity) with strong riverine flow influence. A reference station was analysed at the same time. Physical parameters (grain size), geochemical characteristics (amount of C and N in organic matter) and biological components (phytobenthos, malacofauna and bacteria) clearly showed some important transformations of the sedimentary biota. These transformations correspond essentially to an elimination of fine and medium sedimentary fractions related to bioturbation activities of fishes. This newly created environment is more oxygenated and richer in particulate organic matter (> 10 μm). It is thus colonised by a bacterial flora with a predominance of asporogenous Gram-negative bacilli by which glucose in pure culture is little metabolized. Predation with this environment generates a total disappearance of the benthic malacofauna which is usually very abundant in this type of environment. From these observations, it has not been possible to detect any eutrophication process, in contrast to results obtained in the sediments under floating cages in a continental environment. To conclude, the future of these new culture techniques is discussed for the aquaculture station in Layo (Ivory Coast). This study shows that several recommendations have to be respected when using enclosure cages which seem to represent a promising alternative for the intensive culture of Tilapia guineensis in tropical lagoons.