Wade O. Watanabe

Tilapia Production Systems in the Americas: Technological Advances, Trends, and Challenges

Tilapia is the common name applied to three genera of fish in the family Cichlidae: Oreochromis, Sarotherodon, and Tilapia. The species that are most important for aquaculture are in the genus Oreochromis, including the Nile tilapia, O. niloticus, the Mozambique tilapia, O. mossambicus, the blue tilapia, O. aureus, and O. urolepis hornorum. Fish farmers are now growing many strains of these parent species along with many hybrid strains. Native to Africa and the Middle East, these species have become the second most common farm raised food fish in the world. In the 1960s and 1970s tilapia culture was aimed at the production of food for local consumption, utilizing primarily extensive or semiintensive culture methods with minimal inputs of fertilizer or feeds. However, tilapia culture has expanded rapidly during the last decade as a result of technological advances associated with the intensification of culture practices. These include the development of new strains and hybrids, monosex male culture, formulated diets, a variety of semiintensive and intensive culture systems (e.g., ponds, cages, tanks, and raceways) and the utilization of greenhouses, geothermal, or industrial waste heat and advanced water treatment methods. Marketing programs have also nurtured a growing demand for tilapia in domestic and international markets. Annual worldwide production of cultured tilapia was less than 200,000 metric tons (mt) in 1984 and increased to 1,100,000 mt in 1999. In the Americas, the increased production of farmed tilapia is due in large part to their adaptability to a diverse array of production systems. These include subsistence level, extensive pond culture in the Eastern Caribbean, integrated animal-fish culture in Guatemala and Panama, semiintensive pond culture in Honduras, intensive pond culture in Colombia, Costa-Rica and Jamaica, semiintensive cage culture in several countries, intensive flowthrough tank and raceway culture in the U.S., and a variety of highly intensive indoor recirculating tank culture in the U.S. In addition, there is increasing production of tilapia in shrimp ponds in Ecuador to ameliorate shrimp disease problems. In this article, representatives of various systems are compared with respect to technological approaches and constraints. Poor management of tilapia genetic resources is causing a loss of productivity, and research in genetics and selective breeding will be needed to improve production efficiency, fillet yields, and environmental tolerance. Continuing nutritional studies will also be needed to increase efficiency and profitability. With intensification, infectious diseases have become more serious, and fish health management through biosecurity procedures, environmental manipulation, reduction of stress, nutrition, genetics, and the use of prophylactic therapeutics will be essential. Increasing waste production will require novel methods for integrating tilapia culture with the production of other valuable crops to maximize nutrient recovery and minimize pollution. Market development and quality control will be critical to ensure market growth.

The ontogeny of salinity tolerance in the tilapias Oreochromis aureus, O. niloticus, and an O. mossambicus × O. niloticus hybrid, spawned and reared in freshwater

Abstract The ontogeny of salinity tolerance was studied in the tilapias Oreochromis aureus, O. niloticus, and an O. mossambicus (♀) × O. niloticus (♂) (M × N) hybrid, spawned and reared in freshwater. Several indices were used as practical measures of salinity tolerance: (1) Median Lethal Salinity — 96 h (MLS-96), defined as the salinity at which survival falls to 50%, 96 h following direct transfer from freshwater to various salinities; (2) Mean Survival Time (MST), defined as the mean survival time over a 96 h period, following direct transfer from freshwater to full seawater (32‰); and (3) Median Survival Time (ST50), defined as the time at which survival falls to 50% following direct transfer from freshwater to full seawater. No significant age-specific differences in salinity tolerance were observed in either O. aureus or O. niloticus on the basis of the MLS-96 index. Mean MLS-96 values over all ages from 7 to 120 days post-hatching were 18.9‰ for O. niloticus, and 19.2‰ for O. aureus. In contrast, the M × N hybrid exhibited relatively greater changes in salinity tolerance with age, MLS-96 ranging from 17.2‰ at 30 days post-hatching to 26.7‰ at 60 days post-hatching. Distinct age-specific differences in salinity tolerance were observed in all three on the basis of the MTS and ST50 indices. These ontogenetic changes in salinity tolerance were determined to be more closely related to body size than to chronological age. No consistent relationship was observed between salinity tolerance and condition factor. The practical implications of these findings for the saltwater culture of tilapias are discussed.

Culture of Florida red tilapia in marine cages: the effect of stocking density and dietary protein on growth.

Growth survival and feed conversion were studied in juvenile, monosex male Florida red tilapia (8.78 g average wt.) held in sea cages on Great Exuma, Bahamas. Twenty-four floating cages (1 m3) were anchored in a sea pass and stocked at densities of 100, 200, and 300/m3 and fed 84 days on commercially prepared diets containing 28 or 32% protein. Final mean weights were higher for fish fed the diet with 28% protein (average=176.8 g) than those fed at 32% protein (average=166.4 g), under all densities. Final biomass densities increased with increasing stocking density (range=16.1–52.2 kg/m3) and were higher for fish fed the 28% protein diet than those fed the 32% protein diet under all densities. Daily weight gain (average=1.94 g/day), specific growth rate (average=3.54%/day), and survival (average=97.9%) were higher and feed conversion ratios (average=1.88) lower for fish fed the 28% protein diet than for those fed the 32% protein diet under all densities. No significant effects of stocking density on these parameters were observed. A significant effect of stocking density on final size variation was evident, with greater coefficients of variation of body weights and lengths among fish reared at a density of 100/m3 (average=26.0%; 8.51%) than among those reared at higher densities (average=20.8%; 6.87%). In-cage dissolved oxygen fell to <3 ppm during the study due to declining ambient levels, suggesting that higher biomass densities are attainable, given higher ambient dissolved oxygen.

Combined effects of photoperiod and salinity on growth, survival, and osmoregulatory ability of larval southern flounder Paralichthys lethostigma

Abstract The southern flounder, Paralichthys lethostigma , is an important commercial and recreational marine flatfish that inhabits estuaries and shelf waters in the south Atlantic, from North Carolina through the Gulf coasts, with the exception of south Florida. Because juvenile and adult fish are highly euryhaline, it is a prime candidate for aquaculture. Methods for captive spawning of southern flounder are well developed; however, information on optimal culture requirements of the early larval stages is required for reliable mass production of juveniles. To determine the optimal photoperiod and salinity conditions for culture from hatching to day 15 post-hatching (d15ph), embryos were stocked into black 15-l tanks (75 l −1 ) under four photoperiods (24L:0D, 18L:6D, 12L:12D, and 6L:18D) and two salinities (25 and 34 ppt) in a 4×2 factorial design. Temperature was 18 °C, light intensity was 150 lx, and aeration was 50 ml min −1 . Significant ( P −1 ; and 84% vs. 76% water, respectively), suggesting stress and nonadaptation to 25 ppt, a salinity more nearly isoosmotic than full-strength seawater. Since larvae from both salinity treatments were neutrally or positively buoyant at 34 ppt, but negatively buoyant at 25 ppt, larvae reared at 25 ppt probably allocated energy to maintain vertical positioning, compromising growth and survival. The results demonstrate that growth and survival of early-stage southern flounder larvae are maximized under long photoperiods of 18–24L and in full-strength seawater. Longer photoperiods probably extend the time larvae have for feeding, while full-strength seawater salinity optimizes buoyancy and vertical positioning, conserving energy. The results show that early larval stage southern flounder larvae are not entirely euryhaline, which involves not only the ability to osmoregulate, but to conserve energy under reduced buoyancy. This is consistent with suboptimal vs. maximal growth of larvae reared at 25 and 34 ppt, respectively, under 18L (i.e., photoperiod×salinity interaction). This is also consistent with other reports that tolerance to lower salinities in these euryhaline flatfish increases post-metamorphosis when transition from a pelagic to benthic existence alleviates the need to counteract reduced buoyancy.

The effects of temperature and salinity on growth and feed utilization of juvenile, sex-reversed male Florida red tilapia cultured in a recirculating system

Abstract In two experiments, juvenile, sex-reversed male Florida red tilapia (avg. wt.=0.56–1.20 g) were stocked into forty-two 0.33-m 3 indoor tanks at a density of 74 fish m −3 and growth and feed utilization compared for 54–58 days at temperatures of 22, 27 and 32°C and at salinities of 0 and 18 ppt (experiment one) or at 18 and 36 ppt (experiment two) under a 12 L: 12 D photoperiod. Fish were fed twice daily to satiation a 32% protein diet. Each treatment consisted of seven replicate tanks supported by a recirculating water system. While growth rates generally increased with increasing temperature and were markedly lower at 22°C than at 27 and 32°C, salinity modified the effects of temperature on growth: at 0 ppt, feed consumption and growth reached a maximum at 27°C, while at 18 and 36 ppt, consumption and growth were highest at 32°C. Under all temperatures, feed consumption and growth were higher at 18 ppt than at 0 or 36 ppt. The results suggested that, in freshwater, heating water to temperatures above 27°C is not justifiable, while at 18 or 36 ppt, heating water to 32°C can maximize growth rates without lowering growth efficiency. An important advantage of brackishwater (18 ppt) rearing under conditions of suboptimum temperatures was further suggested.

Salinity tolerance of Nile tilapia fry (Oreochromis niloticus), spawned and hatched at various salinities

Abstract Fertilized eggs of the Nile tilapia ( Oreochromis niloticus L.) spawned in freshwater, were removed from mouthbrooding females, 1 day post-spawning and artificially incubated at elevated salinities. At 6 days post-hatching, mean survivals of 85.5, 84.4, 82.5, 56.3, 37.9, 20.0 and 0% were recorded for broods incubated at salinities of 0, 5, 10, 15, 20, 25 and 32 ppt, respectively. Fertilized eggs exhibited a 96-h median lethal salinity (MLS-96) of 18.9 ppt, a value identical to that of 7- to 120-day-old fry and fingerlings. Fertilized eggs exhibited a higher median survival time (ST 50 = 978 min) than 7- to 395-day-old fry and fingerlings (ST 50 = 28.8–179.0 min). The salinity tolerances of fry spawned at various salinities and fry spawned in freshwater but hatched at various salinities, were determined using the median survival time (ST 50 ), mean survival time (MST) and 96 h-median lethal salinity (MLS-96) indices. For comparative purposes, fry spawned and hatched in freshwater were acclimatized to various salinities and their salinity tolerance determined. Fry salinity tolerance progressively increased with increasing salinity of spawning, hatching, or acclimatization. However, at equivalent salinity, early exposure (spawning) produced progeny of comparatively higher salinity tolerance than those spawned in freshwater and hatched at elevated salinity. Similarly, at equivalent salinity, progeny spawned in freshwater but hatched at elevated salinity exhibited higher salinity tolerance than those spawned and hatched in freshwater, then acclimatized to an elevated salinity. The utility of these methods of early salinity exposure toward the saltwater culture of tilapias is discussed.

Progress in controlled breeding of Nassau grouper (Epinephelus striatus) broodstock by hormone induction

Abstract Human chorionic gonadotropin (HCG), luteinizing hormone-releasing hormone analogue (LHRH-a), and carp pituitary homogenate (CPH), used alone or in various combinations, were tested as spawning agents in captive E. striatus broodstock. Fifty hormone-induced strip-spawning trials were attempted using a two-injection sequence in which a priming dose (PD) was followed 24 h later by a resolving dose (RD). Hormone treatment strategies tested included, HCG alone (PD = 1000 IU kg −1 bw, RD = 500 IU kg −1 bw), LHRH-a alone (PD = 50–100 μg kg −1 bw, RD = 100–200 μg kg −1 bw), HCG (500 IU kg −1 bw) in combination with LHRH-a (50–100 μg kg −1 bw) as priming or resolving doses, and CPH (PD = 10 mg kg −1 bw) in combination with LHRH-a (RD = 50–100 μg kg −1 bw). As an alternative to hormone injection, intramuscular implantation of a cholesterol pellet containing LHRH-a (200–250 μg) was tested in two females. Females with mean oocyte diameters ranging from 482 to 561 μm were suitable for hormone-induced spawning. Oocyte diameter increased to 524–708 μm within 24 h of the priming dose and to 852–945 μm within 9–16.4 h following the resolving dose. Average diameter of spawned (water hardened) eggs ranged from 879–978 μm. Although fertilization rate (0–94.7%) varied widely among trials, successful spawnings (fertilization rate ≥ 50%) were obtained in all of the hormone strategies tested. Use of different hormones in combination showed no advantage over a single-hormone strategy. As HCG appeared to cause an immune response, LHRH-a is recommended for repeated application. Implantation of LHRH-a produced variable results, inducing ovulation in one female, but apparently inducing sex reversal in the other.

Growth, feed conversion and protein utilization of Florida red tilapia fed isocaloric diets with different protein levels in seawater pools

Abstract Twelve outdoor pools (10 m 3 ) receiving flow-through seawater (37 ppt) were stocked with sexreversed male Florida red tilapia fingerlings (10.6 g mean wt.) at a density of 25 fish/m 3 . Three isocaloric diets containing 20%, 25% and 30% protein of equal quality were tested for effects on fish growth, feed and protein utilization, and carcass composition during growout through full marketable size. Growth rate was high for all diets, with mean weight ranging from 440 to 464 g after 120 days, and survival ranging from 97.0 to 97.5%. There were no significant differences among diets in survival, specific growth rate, daily weight gain, feed consumption and conversion, carcass composition, and fish condition. However, protein efficiency ratio was significantly higher for the 20% protein diet than for diets with higher protein levels. The results demonstrate that Florida red tilapia can be reared in seawater from fingerling through marketable sizes more economically on a 20% protein diet than on diets containing higher protein levels.

Observations on the reproductive performance of Nile tilapia (Oreochromis niloticus) in laboratory aquaria at various salinities

Abstract The reproductive performance of yearling Oreochromis niloticus broodstock was monitored under laboratory conditions at various salinities and results compared with the performance of an older (2- to 3-year) broodstock in freshwater. Spawning was observed in salinities ranging from freshwater to full seawater (32 ppt). Extremely poor hatching success was obtained with eggs spawned in full seawater. Mean hatching successes were similar for eggs spawned by yearling females in freshwater (30.9%), 10 ppt (32.7%) and 15 ppt (36.9%). Mean hatching success was considerably higher for eggs spawned at 5 ppt (51.6%) and compared with that obtained with eggs spawned by older females in freshwater (54.2%). Egg and fry production per female was much greater in the older broodstock in freshwater than in yearling females in water of any salinity. Egg and fry production per unit weight was greater in yearling females in salinities of 5–15 ppt than in older females in freshwater.

Hatchery study of the effects of temperature on eggs and yolksac larvae of the Nassau grouper Epinephelus striatus

Abstract The effects of temperature on eggs and yolksac larvae of the Nassau grouper (Epinephelus striatus) were examined under controlled, hatchery conditions. Artificially-fertilized eggs, obtained by induced spawning of captive adults, were stocked (36 eggs per 1) into 15 500 1 cylindroconical indoor tanks at temperatures of 26, 28 and 30 °C, with five tanks per treatment. A salinity of 37 g l−1 and a photoperiod of 12 L: 12 D were maintained. Incubation time to hatching was inversely related to temperature, decreasing from 24.9 h post-fertilization (p.f.) at 26 °C to 20.4 h p.f. at 30 °C, but hatching success (avg. = 82.5%) did not vary with temperature. Survival of pre-feeding larvae declined more rapidly at the higher temperatures to 91.4, 80.7 and 42.2% by Day 1 p.h. at 26, 28 and 30 °C, respectively, indicating that early survival was influenced by factors unrelated to feeding. Development time to the first-feeding stage was inversely related to temperature, decreasing from 86 h p.f. (2.54 d p.h.) at 26 °C to 71 h p.f. (2.11 d p.h.) at 30 °C. Lower temperatures delayed starvation, with survival falling to 32.3, 9.3 and 1.2% by Day 4 p.h. at 26, 28 and 30 °C, respectively. A temperature of 26 °C is deemed advantageous to higher temperatures for incubating eggs and for rearing first-feeding larvae, although even lower temperatures may be feasible. Temperatures within an ecological range can markedly influence development rates of E. striatus eggs and yolksac larvae and hence, dispersal potential, first-feeding and survival in the field.