Tuna Farming Research Articles

Welfare implications of closed-cycle farming of Atlantic bluefin tuna (Thunnus thynnus)

There is an increased demand for tuna meat to supply the growing global sushi and sashimi market. Current methods to farm tunas, especially Atlantic bluefin tunas (ABFTs; Thunnus thynnus), are unsustainable. This is driving a movement towards closed-cycle ABFT aquaculture, i.e., farming tuna from spawning and hatching to slaughter on land, to try and meet the demand for these fish. Tunas are not domesticated species and thus face different challenges in terms of closed-cycle aquaculture when compared to other farmed fish species. Tunas also possess unique physiological traits such as regional endothermy and ram ventilation which affect their needs and how they are farmed. No current global standards exist to measure or monitor ABFT welfare in captivity, because there are many unknown factors surrounding ABFT welfare in aquaculture settings. There is a need to conduct studies that measure the baseline physiological parameters of ABFT in closed-cycle systems. Issues such as manipulation of breeding cycles, tank design, and slaughter procedures need attention and further research is required before such welfare indicators can be established. Stress is an overarching concern for animal welfare. In particular, pre-slaughter crowding and stress negatively affect the quality of the meat produced due to lactic acid buildup in the red muscle. Further research needs to be conducted throughout all life stages in terms of both animal welfare implications and the commercial viability of farmed ABFTs.

Antioxidant and Metabolic Response to Acute Acidification Stress of Juvenile Yellowfin Tuna (Thunnus albacares)

This study aimed to explore the impact of acute acidification on the antioxidant, metabolic performance, and liver histology of juvenile yellowfin tuna. The experiment subjected juvenile yellowfin tuna to a pH gradient environment of 8.1, 7.6, 7.1, and 6.6 for 48 h. The findings indicate that a seawater pH of 7.1 significantly impacts the antioxidant and metabolic systems of the juvenile yellowfin tuna in comparison to the control group. At pH 7.1, there were observed increases in glutathione reductase (GR), total antioxidant capacity (T-AOC), lactate dehydrogenase (LDH), hexokinase (HK), pyruvate kinase (PK), sodium-potassium ATPase (Na+K+-ATP), and calcium-magnesium ATPase (Ca2+Mg2+-ATP). Conversely, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), and triglycerides (TGs) were not significantly different across the treatment groups. However, an increase in transaminases at pH 7.1 suggested potential liver damage, which was further supported by observed structural liver tissue degeneration and hepatocyte vacuolation. In conclusion, under conditions of acute acidification stress, there is a decrease in antioxidant capacity and a suppression of metabolic levels in juvenile yellowfin tuna, leading to oxidative damage. This study lays the foundation for an in-depth understanding of the response mechanisms of juvenile yellowfin tuna in response to seawater acidification as well as healthy tuna farming in the broader context of seawater acidification.

Mechanisms of Digestive Enzyme Response to Acute Salinity Stress in Juvenile Yellowfin Tuna (Thunnus albacares).

This study investigates the effect of a sudden change in salinity for 48 h on the digestive enzyme activity of juvenile yellowfin tuna. The treatment included a control salinity of 32‱ in natural seawater and an experimental salinity of 29‱. Acute stress experiments were carried out on 72 juvenile yellowfin tuna (646.52 ± 66.32 g) for 48 h to determine changes in digestive enzyme activity in different intestinal sections over time (0 h, 12 h, 24 h, 48 h). The activities of pepsin, trypsin, α-amylase, lipase, and chymotrypsin in the digestive organs (stomach, foregut, and pyloric ceca) of juvenile yellowfin tuna were measured. Pepsin and pancreatic protease in the experimental group were significantly lower than in the control group (p < 0.05). α-amylase showed a fluctuating trend of decreasing and then increasing, and its activity trend was pyloric ceca > foregut > stomach. The lipase activity of gastric tissues decreased at the beginning and then increased, reaching a minimum at 24 h (2.74 ± 1.99 U·g protein-1). The change of lipase in the pyloric ceca and foregut was increasing and then decreasing. The lipase activity trend was pyloric ceca > foregut > stomach. The chymotrypsin showed a decreasing and increasing trend and then stabilized at 48 h with a pattern of pyloric ceca > foregut > stomach. Similarly, the gut villi morphology was not significantly altered in the acutely salinity-stressed compared to the non-salinity-stressed. This study suggests that salinity may change the digestive function of juvenile yellowfin tuna, thereby affecting fish feeding, growth, and development. On the contrary, yellowfin tuna is highly adapted to 29‱ salinity. However, excessive stress may negatively affect digestive enzyme activity and reduce fish digestibility. This study may provide a scientific basis for a coastal aquaculture water environment for yellowfin tuna farming, which may guide the development and cultivation of aquaculture.

Preliminary Study of Age and Growth of Bluefin Tuna Thunnus thynnus (Scombridae) from Fish Farm in the East of Tunisia

The Atlantic bluefin tuna, Thunnus thynnus, is a fish of high economic interest. Nevertheless, its biology is not yet well understood. The objective of the study is to describe the age and the growth of the bluefin tuna collected from the tuna farm located in the East area of Tunisia (Salakta-Mahdia). The age is estimated by counting the annuli on the cross sectioned dorsal fin ray and the Von Bertalanffy growth equation is established: Lt = 390×(1 – exp(−0.07x(t + 1.23)). The estimated age ranges from 3 to 14 years. Most of the catch is composed of bluefin tuna of age class 4 to 7. A positive allometric growth is established for fattened bluefin tuna. The condition factor ranges from 0.98 to 2.63 with a mean value of 1.79 ± 0.26. The mean condition factor shows an increasing trend with age.

Direct Ageing and Growth using Dorsal Fin Spines of Bluefin Tuna Thunnus thynnus (Scombridae) Reared in Sea Cages and a Comparison with Wild Populations

The main objectives of this study were to estimate the age and growth of reared Atlantic bluefin tuna and to reveal possible differences in growth between reared and wild specimens. A total of 806 specimens, ranging from 102 to 284 cm in length, were sampled from a Greek tuna farm in the Mediterranean Sea. The first spine of the first dorsal fin was used to estimate the age. Estimated ages ranged from 3 to 20 years, and the reproducibility of the ageing method was high. The proportion of the mean number of missing annuli per age due to vascularization ranged from 27.8 to 40.0%, with an average loss of 33.5%. No significant differences in the number of missing annuli were observed between 6–month and 18–month reared specimens of the same age group. The von Bertalanffy growth model was fitted a) to mean FL-at-age data and b) to mean RW-at-age data, and the growth equations found were: Lt = 296.6[1 – e(−0.114) (t + 1.026)] and Wt = 591.6[1 – e(−0.100)(t + 1.755)]3. Our results showed that the rearing process accelerates the growth of the Atlantic bluefin tuna and this was also evident in the calcified structure. In comparison with previous studies of growth in wild bluefin tuna from the Mediterranean Sea, mean weights at age of the reared fish were higher than those from wild fish in all age groups and lengths at age of the reared bluefin tuna were higher in younger fish, up to 6 years old.

Optimization of stocking density and shipping duration for transportation of Pacific bluefin tuna, Thunnus orientalis (Temminck et Schlegel), eggs, and experimental verification of polyethylene glycol treatment to reduce collision damage

AbstractPacific bluefin tuna (PBT), Thunnus orientalis, is one of the most important species for aquaculture worldwide. For the conservation of this species and sustainable development of the tuna farming industry, production based on closed‐cycle aquaculture should be promoted. In this study, to develop an efficient method for transporting PBT eggs, we simulated egg transportation to optimize stocking density and shipping duration, which are the two variables critical to the transportation procedure of PBT. Based on the findings of this study, we concluded that PBT eggs should be transported at a density of 1 × 104 eggs/L within 12 h in the field. Furthermore, we showed that collisions between eggs during transportation negatively affected the normal hatching rates of eggs, and polyethylene glycol (PEG) treatment (at 1000 μg/mL for 12 h) could reduce such damage. Our results suggest that PEG treatment is a practical approach that contributes to the stable transportation of PBT eggs, particularly in cases where the effects of physical shock damage is considerably increased.

An Overview of Atlantic Bluefin Tuna Farming Sustainability in the Mediterranean with Special Regards to the Republic of Croatia

Atlantic bluefin tuna (Thunnus thynnus) is the most important tuna species in Mediterranean tuna fishery and a valuable commodity on the global fish market. Croatia is a pioneer in tuna farming in the Mediterranean and the only country that has the exclusive right to farm wild-caught juvenile tuna (8 to 30 kg). This paper identifies key challenges to the sustainability of current farming and fattening practices, primarily economic and environmental, and possible solutions to overcome these challenges. This paper analyses data on tuna catch and aquaculture production (FAO FishStatJ and EU-Eurostat database) and updates the latest literature on farming practices, production challenges related to biotechnical, economic and environmental issues, the market and current legislation in Croatia, as well as fattening in other Mediterranean countries. Tuna capture-based aquaculture is attractive to investors because it promises high returns, but the sustainability of intensive tuna farming and fattening is questionable and raises many ethical issues. Tuna farming and fattening relies on wild fish for stocking and feeding, and further expansion of tuna farming and fattening is limited by the size of wild tuna and small fish populations. To meet the growing global demand for tuna and to conserve wild tuna stocks, further investments are needed. The knowledge gained in Croatian tuna farming is valuable for future sustainable close-cycled tuna farming in the Mediterranean. Due to its good environmental status, the availability of small pelagic fish, the availability of a highly qualified and well-organised labour force, the good cooperation between producers and researchers, and the application of modern farming technologies, ABFT farmed in Croatia have high quality and a good reputation on the market. The main weakness of Croatian tuna farming is that the entire industry is dependent on the Japanese market, but this can be overcome by the possibility of product diversification for new markets, including the tourism industry.

Changes in Condition Factor, Hepatosomatic and Gonadosomatic Index of Yellowfin Tuna (Thunnus albacares) in Captivity

The necessity for tuna products in the world community continues to increase, while production relies only on catching, thus causing overfishing. Therefore, breeding technology to support tuna farming is fundamental to be developed. Yellowfin tuna farming in Indonesia has been successful in cultivating broodstock. This paper discusses biometric data that changes during cultivation, such as condition factor, hepato and gonadosomatic indexes compared with wild captured. Data were collected from young tuna to broodstock and compared with wild captured such as fork length, body, liver and gonad weight. The condition factor (K) of cultivated tuna (1.5-2.5) was higher compared with wild captured (1.5-2.0). Similarly, the value of cultivated tuna’s hepatosomatic index (HSI) was higher (0.63-1.14). In contrast, the gonadosomatic index (GSI) of wild captured yellowfin tuna was higher (&gt;0.5) compared with cultivated yellowfin tuna in a circular concrete tank (0.4) but lower than that cultivated in a floating net cage (&gt;1.4). Maintenance of broodstock in the tank with a lower GSI value means the number of eggs produced is relatively lower than its natural counterpart. At the same time, the high GSI value of cultivated broodstock in FNC shows better results than wild captured broodstock.

A Study on the Building of Tuna Farming in Floating Offshore Wind Power Generation Field at East Sea

We need measures that can come up with alternative about fishery living zone and enhance local acceptance for responding to the increase in the proportion of renewable energy production and construction of 12GW Offshore wind power according to Korea’s Renewable Energy 3020 initiative and Korean-version New Deal. In this study, We suggest that differentiation plans of co-location model in connection with offshore wind power generation suitable for the East Sea. The East Sea is an optimal site for building of a floating offshore wind power generation(FOWPG) field. It is expected that economic effects like energy production, aquatic resource development and tourism industrialization by farming bluefin tuna which is high valued fish and suitable for offshore aquaculture on public waters in FOWPG field. And we can confirm that budget reduction, smart management by sharing operation management technology and increase in fishermen income.

Plastic Responses of Gilthead Seabream Sparus aurata to Wild and Aquaculture Pressured Environments

Fish farms, as artificial marine structures with a constant food supply, have a high capacity to attract surrounding wild fish. Different phenotypes of abundant gilthead seabream have been recorded in natural and aquaculture pressured environments in the eastern Adriatic Sea, where the influence of tuna farming on plastic traits associated with habitat use and foraging behaviour remains largely unknown. Several traits, such as body and otolith shape, external colouration, diet preference, and proximate tissue content, were analysed to examine habitat selection of the tuna farm-associated phenotype in comparison to wild and farmed phenotypes. Foraging behavioural shifts in prey selectivity, from hard-shelled bivalves towards soft textured baitfish feed, and local hydrodynamic conditions have initiated plastic responses in farm-associated seabream. Consequently, morphological traits connected with feeding and swimming performance and paler vs. vivid body colouration patterns differed between wild and farm-associated fish, highlighting the existence of resource polymorphism in gilthead seabream. While otolith shape proved to be a reliable phenotypic tracer in distinguishing farmed from wild and farm-associated fish, reduced sensitivity was found between individuals residing in the vicinity of tuna farms and wild ones. To fully understand the impact of fish farms on associated gilthead seabream and its plastic response with a distinctive morph outcome, the underlying molecular mechanisms involved in the regulation of alternative phenotypes needs to be investigated.

Experimental investigation on the fluid–structure interaction of a flexible net cage used to farm Pacific bluefin tuna (Thunnus orientalis)

Resource protection of Pacific bluefin tuna (Thunnus orientalis) fish catching has become stringent over the past years. Meanwhile, tuna farming in Japan, the largest consumer of this fish, using a circular flexible net cage is continuously growing as a promising business. A stable aquaculture production of tuna can be achieved by understanding the characteristics, such as a clean environment and space in the net cage and flow inside and near the circular flexible net cage. We measured the drag force, cage deformation, and flow field inside and around a scaled net cage model composed of different bottom weights under various incoming current speeds in a flume tank. Results indicated that the drag force and cage volume increased and decreased, respectively, with the bottom weight. Owing to the significant deformation of the flexible net cage, a complex fluid–structure interaction occurred and a strong negative correlation between the drag force and cage volume was obtained. Furthermore, an area where the current speed was often reduced was identified. The intensity of this reduction depended on the incoming current speed. However, in particular cases, this reduction did not occur, or a local acceleration of the fluid was observed. In this work, the depth data of several positions on the net cage were also analyzed to verify if it could be used to estimate the cage volume. The findings of this study can be used to understand and design optimal flexible net cage structures, which can be used for modern aquaculture.

A Dynamic Energy Budget simulation approach to investigate the eco-physiological factors behind the two-stanza growth of yellowfin tuna (Thunnus albacares)

The growth of yellowfin tuna has been the subject of considerable research efforts since the early 1960s. Most studies support a complex two-stanza growth pattern with a sharp acceleration departing from the von Bertalanffy growth curve used for most fish populations. This growth pattern has been assumed to result from a combination of physiological, ecological and behavioral factors but the role and contribution of each of them have not been addressed yet. We developed a bioenergetic model for yellowfin tuna in the context of Dynamic Energy Budget theory to mechanistically represent the processes governing yellowfin tuna growth. Most parameters of the model were inferred from Pacific bluefin tuna using body-size scaling relationships while some essential parameters were estimated from biological data sets collected in the Indian Ocean. The model proved particularly suitable for reproducing the data collected during the Pacific yellowfin tuna farming experience conducted by the Inter-American Tropical Tuna Commission at the Achotines Laboratory in Panama. In addition, model predictions appeared in agreement with knowledge of the biology and ecology of wild yellowfin tuna. We used our model to explore through simulations two major assumptions that might explain the existence of growth stanzas observed in wild yellowfin tuna: (i) a lower food supply during juvenile stage in relation with high intra- and inter-species competition and (ii) ontogenetic changes in food diet. Our results show that both assumptions are plausible although none of them is self-sufficient to explain the intensity of growth acceleration observed in wild Indian Ocean yellowfin tuna, suggesting that the two factors may act in concert. Our study shows that the yellowfin growth pattern is likely due to behavioral changes triggered by the acquisition of physiological abilities and anatomical traits through ontogeny that result in a major change in intensity of schooling and in a shift in the biotic habitat and trophic ecology of this commercially important tuna species.

Persistent organic pollutants in tissues of farmed tuna from the Adriatic Sea

This study investigated the levels and distribution of polychlorinated biphenyls (PCBs) and organochlorine pesticides in three tissue types of farmed Bluefin tuna (Thunnus thynnus): muscle, liver and branchiae. Seven adult species were caught in 2015 at a tuna farm in the Croatian Adriatic. The organochlorine compound levels decreased in the following order: liver > muscle > branchiae while contaminant distribution in all three tissues followed the same order: ΣPCB ≫ ΣDDT > ΣHCH ~ HCB. The found POP levels indicated moderate pollution of farmed tuna and were below all limits set by current laws. Furthermore, no cytotoxic effect of the POP mixture extracted from tuna liver samples on human neuroblastoma cells was observed.

In vivo cultivation of tuna blood fluke Cardicola orientalis in terebellid intermediate hosts

Some fish blood flukes of the genus Cardicola (Aporocotylidae) are considered important pathogens of farmed/ranched tuna, Thunnus spp. Infections with Cardicola spp. might obstruct the blood flow in the gills via massive accumulations of eggs and often lead to mass mortalities in captive tuna. At present, oral administration of an anthelminthic drug, praziquantel is the most effective treatment, but the tuna farming industries are seeking non-drug control measures. Development of prophylactic and holistic measures have been difficult, owing to a lack of basic knowledge about these parasites. Unlike other trematodes which use molluscs, blood flukes of marine actinopterygian fish use terebellid polychaetes as intermediate hosts. However, information about the development of Cardicola spp. within intermediate hosts is very limited. Recent success in Cardicola opisthorchis sporocyst transplantation into the host polychaete has opened possibilities for the cultivation of Cardicola in the laboratory. Here, we conducted several transplantation trials with another tuna blood fluke, Cardicol orientalis, into its natural and surrogate polychaete hosts. Cardicola orientalis sporocysts were injected into a total of 195 Nicolea gracilibranchis, the natural host, and clear sporocyst development and reproduction was observed in 32 recipients (overall success rate 16.4%). The production of daughter sporocysts in the transplanted polychaete occurred within 14 days post injection, and one sporocystogenous cycle took approximately 4 weeks. Serial passage culture via transplantation of in vivo-cultured sporocysts was also achieved, but with limited sporocyst reproduction. In addition, sporocysts were successfully retrieved from six and one individuals of the surrogate hosts, Thelepus setosus (n = 10) and Thelepus japonicus (n = 5), respectively. These results indicate that the in vivo cultivation of C. orientalis sporocysts is possible, not only in its natural host but also in other terebellids, although the problems of high mortality and inconsistency in successful transplantation need to be resolved.

The Peculiarities and Farming Challenges of Atlantic Bluefin Tuna (Thunnus thynnus, L. 1758)

Abstract The aim of this paper is to provide an overview of bluefin tuna, with special regard to its farming challenges. Tuna is one of the most prominent species in fisheries worldwide. The high market value of tuna stocks has led to intensified fishing pressure that resulted in drastic population reductions in every ocean where these fish are found. It is very difficult to obtain the necessary data for the appropriate stock assessment analysis, and there is a very high degree of uncertainty in the models used to evaluate Atlantic bluefin tuna stocks. Tuna-farming could help reduce pressure on the tuna population, but the problem is that the majority of cage-farmed fish is caught in its natural environment (wild population), and thus is fattened or farmed to a certain size. Additionally, the challenges in tuna farming are numerous. Tuna is a fast swimmer, a large energy and oxygen consumer, therefore consuming a large portion of available food to maintain its metabolism. However, due to its delicious taste, high market price and a large demand for this species, pressure will probably continue to grow in the future. Therefore intensive farming, which implies the full breeding cycle in captivity, remains one of the possible solutions that could help reduce the pressure on the tuna population.

Effects of Design Factors on Drag Forces and Deformations on Marine Aquaculture Cages: A Parametric Study Based on Numerical Simulations

In Japan, the marine aquaculture net cage has an important role in farming pacific bluefin tuna farming in oceans, and the design of the net cage needs to ensure robustness against hostile oceanic conditions. Accordingly, this study focuses on the drag forces and the cage volume of the net cage, and on their variations induced by different design parameters (netting solidity ratio, netting height, and bottom weight). A series of parametric studies on drag force and deformation of the net cage was conducted using a numerical simulation model. Accordingly, the contribution of each parameter to the drag and volume was analyzed using a generalized additive model. The results indicate that the bottom weight had the highest contribution to the holding ratio of the cage volume, whereas the netting height had the highest contribution to the drag coefficient of the net cage. Finally, a fast prediction model was created by a backpropagation (BP) neural network model and was examined for the accurate prediction of the objective variables.

Improvement of the Pacific bluefin tuna (Thunnus orientalis) reference genome and development of male-specific DNA markers

The Pacific bluefin tuna, Thunnus orientalis, is a highly migratory species that is widely distributed in the North Pacific Ocean. Like other marine species, T. orientalis has no external sexual dimorphism; thus, identifying sex-specific variants from whole genome sequence data is a useful approach to develop an effective sex identification method. Here, we report an improved draft genome of T. orientalis and male-specific DNA markers. Combining PacBio long reads and Illumina short reads sufficiently improved genome assembly, with a 38-fold increase in scaffold contiguity (to 444 scaffolds) compared to the first published draft genome. Through analysing re-sequence data of 15 males and 16 females, 250 male-specific SNPs were identified from more than 30 million polymorphisms. All male-specific variants were male-heterozygous, suggesting that T. orientalis has a male heterogametic sex-determination system. The largest linkage disequilibrium block (3,174 bp on scaffold_064) contained 51 male-specific variants. PCR primers and a PCR-based sex identification assay were developed using these male-specific variants. The sex of 115 individuals (56 males and 59 females; sex was diagnosed by visual examination of the gonads) was identified with high accuracy using the assay. This easy, accurate, and practical technique facilitates the control of sex ratios in tuna farms. Furthermore, this method could be used to estimate the sex ratio and/or the sex-specific growth rate of natural populations.

Morphological and ecophysiological adaptations of wild gilthead seabream Sparus aurata associated with tuna farms

Morphological and ecophysiological adaptations of wild gilthead seabream Sparus aurata associated with tuna farms

POTENTIAL ENVIRONMENTAL IMPACTS OF TUNA CAGE FARMING IN THE AEGEAN SEA

The present study aimed to investigate the potential impacts of Atlantic Bluefin Tuna ( Thunnus thynnus ) farming in offshore cage systems in the Aegean Sea (Sigacik Bay-Izmir, Turkey), in respect to physico-chemical water quality parameters, nutrient loads, chlorophyll- a , total suspended solids, zooplankton groups, and TRIX index calculations for the potentially affected cage farm area and an unaffected reference site. Concentrations of physico-chemical variables (temperature, salinity, dissolved oxygen, pH) in the study carried out in May and August 2018, were within the acceptable limits for marine aquaculture in terms of water quality characteristics. The concentrations of PO 4 -P, NH 4 -N, and NO 2 -N showed no temporal or spatial changes, and were recorded below 0.01 mg/L (<0.01) for PO 4 -P and NH 4 -N, whereas lower than 0.005 mg/L (<0.005) for NO 2 -N values in both cage and reference stations in May and August 2018 periods. Results showed low levels of TSS (0.33-11.87 mg/L), both in the cage farm area and the reference site, remaining below the general quality criteria of 30 mg/L for marine environment. No eutrophication risk (TRIX index, T<4 ) was observed around the Tuna Cage Farm Site in Sigacik Bay, according to the legislations enacted for “Sensitive Areas of Enclosed Bays where fish farms are not allowed”. Based on these findings, demonstrating highly interactive trophic level variability, it can be concluded that the impacts of the Tuna Cage Farm were not significant, possibly due to the consistent movement of the water in currents in the study area.

Seasonal variation of the phytoplankton community in tuna farms in Bahia de La Paz, southern Gulf of California, Mexico

The phytoplankton community of tuna farms in Bahia de La Paz, southern Baja California, Mexico was studied. Samples were taken from tuna farms near San Juan de la Costa, Rancheros del Mar and from a station in El Mogote, away from the influence of these farms. Water samples were collected monthly (June 2006-May 2007) with a van Dorn bottle at different depths in San Juan de la Costa (0, 25 and 50 m), Rancheros del Mar (0, 15 and 30 m) and El Mogote (0 m) to measure temperature, dissolved oxygen, inorganic nutrients, and chlorophyll-a and to determine phytoplankton composition and abundance. The index of simple dominance, Shannon-Weaver diversity, and Pielou evenness were estimated. The water column was stratified from June to September (~27.5°C) and mixed from October to May (~18.5°C). Nutrient concentrations at the three sampling sites did not increase significantly. Nanophytoplankton dominated, followed by microplanktonic diatoms, and the highest diatom abundance occurred during the warm period. The phytoplankton community was more diverse in San Juan de la Costa than in Rancheros del Mar. In the latter, a superficial bloom of the cyanobacterium Trichodesmium erythraeum (1630×103 cel L -1 ) occurred in September, and in San Juan de la Costa the diatom Pseudo-nitzschia fraudulenta reached the highest abundance (183.8×103 cel L -1 ) in July.