COMUNICACIÓN BREVE

Possibility of culturing Pacific goliath grouper Epinephelus quinquefasciatus in water with different salinities

Posibilidad de cultivo del mero guasa del Pacífico Epinephelus quinquefasciatus en aguas de diferentes salinidades

Lury García N,¹* M.Sc, Frank Chapman Ch,² Ph.D.

¹Universidad del Pacífico, Programa de Tecnología en Acuicultura, Av Simón Bolívar # 54A-10 Los Laureles, Buenaventura-Valle del Cauca, Colombia.
²University of Florida, Program Fisheries and Aquatic Sciences, 7922 NW 71st Street, Gainesville-Florida 32653, USA.

*Correspondence: lurynohemyg3@gmail.com ; fchapman@ufl.edu

Received: March 2014; Accepted: November 2014.

ABSTRACT

Objective. To assess the survival and growth of juvenile Pacific goliath grouper (Epinephelus quinquefasciatus) in captivity at low salinities. Materials and methods. We randomly selected twelve juvenile goliath groupers with an average standard length of 44.2 ± 6.1 cm and 1492 ± 476 g in body weight, and raised them for three months in the laboratory in waters of 32-26, 20, 10 and 5 parts per thousand of salinity. Results. All juvenile Pacific goliath groupers tolerated the initial gradual transfer from full strength seawater to salinities of 32-26, 20, 10, and 5 parts per thousand, which was done over a period of four days. All of them survived and grew in body weight and length during the course of the three-month experiment, in all the treatments of high and low salinity water. The body condition factor (K) for each fish was between 1.5 and 2.4. Conclusions. This is a first time trial that documents a randomized, controlled experiment demonstrating the ability of Pacific juvenile goliath grouper to gradually transfer from full strength seawater to water of lower salinity, and survive and grow well in these brackish waters.

Objetivo. Evaluar la supervivencia y crecimiento de mero guasa del Pacifico (Epinephelus quinquefasciatus) a bajas salinidades en cautiverio. Materiales y métodos. Se seleccionaron al azar doce juveniles de mero guasa de una longitud estándar promedio de 44.2 ± 6.1 cm y 1492 ± 476 g de peso corporal, que fueron criados por tres meses en el laboratorio en aguas de 32-26, 20, 10, y 5 unidades prácticas de salinidad (UPS). Resultados. Todos los juveniles de mero guasa toleraron la transferencia gradual, que se realizó en cuatro días, desde agua de mar a aguas con salinidades de 32-26, 20, 10, y 5 UPS. Igualmente todos sobrevivieron los tres meses, y presentaron ganancia en peso y longitud corporal en todos los tratamientos con niveles altos y bajos de salinidad. Los factores de condición corporal (K), para cada pez estuvieron entre 1.5 y 2.4. Conclusiones. Por primera vez se documenta un experimento de prueba aleatoria controlada; que demuestra la habilidad de juveniles de mero guasa del Pacífico, a poder adaptarse de agua marina a salinidades más bajas que las de su medio ambiente natural, y de crecer en ellas con total supervivencia.

INTRODUCTION

The resources that draw greater commercial interest in the marine fish industry in Colombia are shrimps, lobster, tunas, snappers, mackerels and groupers (1). Of the grouper the most desired is the goliath grouper, its flesh is considered excellent, and high prices in the local and international market are obtained. It is a large species that reaches up to 455 kg in weight and 2.5 m long (2). The biological and ecological characteristics of the species indicate great adaptability to captivity and the ability to endure environmental fluctuations, including salinity (3-5). In captivity, individual fish from 0.5-3.5 kg more than double their weight in 90 to 240 days (3). It could be a marine fish species adaptable to diversification of aquaculture in Colombia. However, there is little information about its adaptability to low salinity conditions and culturing the species under these circumstances (3-5).

Marine aquaculture, including grouper, is principally done in cages suspended in protected areas of the sea or in channels and tanks in farms by the sea (6). Although culturing in cages in the sea is the simplest and most economic initial solution, a viable alternative that protects the environment, economic growth, social and cultural sustainability, principally in Colombia, is culturing marine fish inland (opinion of the authors of this study). Also in the opinion of the authors is that the principal advantages of culturing marine fish in the inland is the possibility of improved control over the environment where the animals are bred, predator control, the option to apply a feeding ration protocol that is efficient and results in weight gain and growth, feeding at required times, and reducing food waste that often occurs in cages, thus lowering feeding costs and increasing the productive efficiency of fish culture.

From the point of view of environmental sustainability, culturing marine fish inland could make use of saline water and land that is not apt for agriculture or farming. Breeding marine fish with a high commercial value would enable a diversification of production risks and profitability, and would offer new opportunities for economic growth and employment in the rural sector. This is especially true for the costal populations that are characterized by having a culture and life style immersed in a mix of traditional agriculture and artisan fishing.

In a recent study it was shown that grouper has the anatomic and physiologic mechanisms of osmoregulation that allows them to keep an adequate balance of salts and water in environments both fresh water and salt water (5). In static bioassays of acute toxicity of 96 hours (CL50-96h) in water with low salinity, the survival of the bass depends on weight (greater than 160g) or body size (5).

Populations of goliath grouper are found on both coasts of Colombia and the species is recognized as Epinephelus itajara in the majority of texts. Recently the population of the Pacific was designed with the scientific name E. quinquefasciatus or Pacific goliath grouper (7). Although genetically different, up to now no apparent differences in the biological and ecological characteristics between the two populations have been observed. In the same way, individuals of both populations have demonstrated a great adaptability in captivity (5). Similarities in the results and interpretation between the two species can thus be assumed.

The objective of this study was to evaluate the survival and growth of Pacific goliath grouper (Epinephelus quinquefasciatus) in brackish water.

MATERIALS AND METHODS

Study site. Experiments were done at the Fish Culture Station facilities of the National Aquiculture and Fishing Authority (AUNAP) Bahía Málaga on the Pacific coast, Valle del Cauca, Colombia (04°06'00” N; 77°21'00” O).

Animals in the experiment. The groupers were young Epinephelus quinquefasciatus (species previously known as E. itajara) collected from the natural marine environment (26-32 parts per thousand of salinity or pps; 35 pps=35 g of salt per liter of solution) close to the station, transported in plastic containers without sedatives, acclimated to captivity in floating cages (3 x 3 x 2 m with plastic mesh openings of 2.5 cm) in the ocean (26-32 pps and 28-32°C), and kept at a density of 20 kg/m3 in inanition for a week before beginning the experiment to ease transition to feeding in captivity.

Identification, handling of specimens and obtaining different salinities. From the group, 12 fish were selected with a standard average length (SL) of 44.2±6.1 cm and 1492±476 of weight; even when the number of fish was low, and there was high standard deviation, each individual represented an independent variable or standard since in this type of acclimation (survival or growth), the physiological singularity of each individual and not necessarily of any group is expressed; the comparison of these variables between groups is only a reference and description. These were taken to the laboratory and were randomly equally divided into 4 tanks with salinities of 5, 10, 20 and 26-32 ppt; the required salinities were obtained by diluting marine water in fresh water until reaching the required salinity which was verified with a refractometer; the salinity of salt water fluctuated between 26 and 32 ppt.

Acclimation to the desired salinity was gradually done over 4 d. The salinity was reduced sea water at 20 ppt during one hour, and kept at this salinity for 24 h; then it was reduced by 15 ppt during one hour and kept at that salinity for 24 h; then it was reduced by 8 ppt and kept at that salinity for 48 h, and finally during one hour the complete transition to fresh water was made. Each fish was marked with a small cut on its fin.

Captivity location and feeding of the specimens. The experiment was performed in tanks of 1500 l (2 x 1 x 1 m), with an interchange of 20% to 30% daily, and constant oxygenation; each system was randomly measured for oxygen, temperature, and salinity with a multiparameter instrument (YSI 85, YSI, Inc., U.S.A.). The fish were fed two times a day with pieces of fresh fish (Opistonema libertate) at 4% its total weight. This percentage was used so as not to introduce too much organic material in the system and thus be able to control the quality of the water.

Survival, feeding, recording measurements and duration of the study. During the experiment it was observed that the survival of individuals and their individual feeding behavior as: consumption or rejection of feed. The assay was done over 12 weeks and every two weeks the fish were individually sampled, with the total weight recorded (g), total length and standard (cm). With this data the averages of weight and size were obtained, both initial and final, the percentage of weight gained, and the condition factor (K= weight * 100/Length^3.056) of each individual; the condition factor was used to evaluate the state of health of the individuals during the experiment. At the end of the experiment the survival rate was calculated.

Data analysis. Data was organized and analyzed using descriptive and parametric statistics with a level of reliability at 95% (alpha of 0.05), on Excel sheets (Excel ver. 12.0, Microsoft Corporation, U.S.A.), Barlett test to establish homogeneity of the variables, and the t-test from Student.

RESULTS

All the young grouper survived the initial acclimation by gradual transfer that was done in four days, from sea water to water with salinities of 32 a 26, 20, 10 and 5 ppt. All the specimens survived the three months of treatment with high and low levels of salinity (Table 1). The fish also easily accepted the consistent feeding of pieces of fresh fish. In every treatment each fish increased in weight and size; but growth rates were very variable so no significant differences were detected (p>0.05) between different salinities (Table 1). Body condition factors for each fish were between 1.5 and 2.4 (Table 1).

DISCUSSION

In this study, the possible similarity in the osmorregulatory adaption of the Pacific goliath grouper population with that of its congener described in the Atlantic (5) is discussed. For the first time an experiment is documented that shows the ability of young Pacific goliath grouper to be gradually transferred from sea water to lower salinities than those of its natural environment and grow in them with complete survival over a period of three months. The corporal condition factors for each fish were between 1.5 and 2.4 (Table 1); similar estimates to the range factors of theoretical condition of 1.6, determined for grouper bass of a similar size captured and predicted by the length-weight relation model reported in the digital fish encyclopedia FishBase (2). The fact that all the fish survived in good health and bodily conformation (k), similar or larger when compared to grouper found in nature, is a significant result of this study and shows the possibility of breeding the species in water with different salinities.

The survival and growth in good health in salinity of 5 ppt is also a good result, since Woo & Wu (8) and Wu & Woo (9) reported that the osmoregulatory capacity in other species of grouper was only between 7 and 30 ppt and these were the only results reported in recent literature. Although the optimal salinity for breeding was not determined, in the experimental salinity of 10 ppt (isosmotic) similar results were observed and even better growth to that observed in a natural environment with salinities around 28-32 ppt, with the explanation that the osmoregulatory processes require energy, so that salt water environments that diminish energy needs help to maximize the growth of the species.

In the case of gilt-headed bream, Sparus aurata, marine species considered to be eurohaline, it has been clearly demonstrated that greater growth occurs when they are acclimated at 12 ppt and not at 6 or 38 ppt (10). Even so, the exact mechanism of the effect of salinity in growth is not completely understood (11). Additionally, during this experiment the grouper were docile and easily adapted to captivity, although some of them had leeches. In other grouper species a lower incidence of diseases especially in waters with lower salinity was noted (8,9).

For several years, a variety of grouper have been commercially cultivated, principally in China, Japan, Taiwan, Southeast Asia and the Middle East, but these practices are mainly based on collecting young fish in the wild and fattening them in captivity until they are at commercial size (6). Sustainable aquaculture practices, however, should depend on seed obtained under domestic conditions. The purpose of this study was to initiate investigations about the growth possibility of grouper in low salinity or freshwater conditions. Eventually the purpose is to organize a group of producers to develop the production technology of eggs and young fish. This is for the aquaculture of marine species in coastal areas or inland in Colombia, an attractive proposition, especially for reducing risks inherent in breeding in cages at high sea, in relation to activities like maintaining, repairing production structures, caring for fish, disease in natural populations and contaminating the benthic community. Additionally, property conflicts, public perfection, and technical matters in selecting the site make it more and more difficult to do ocean aquiculture. The great osmoregulatory capacity of the young of this species (5), as well as the proven capacity to adapt to captivity (3,4), are indicators of the potential of culturing this species in Colombia, not just in marine environments, but also in low salinity and even freshwater conditions.

Acknowledgement

To the fishermen, students at the Universidad del Pacífico, and the leaders at the AUNAP in Bahía Málaga for making the staff available and allowing the use of their installations.

REFERENCES

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