Atlantic Salmon (Salmo salar L.) in Brittany and Lower-Normandy: Preliminary Observations on the General Characteristics of Adults

This paper presents some characteristics (length, weight and age) of adult Atlantic salmon in rivers of Brittany. The data were derived from 1,578 fish caught mainly by rod and line; the remainder being from net catches in estuaries and small samples taken outside the fishing season. The bulk of the fish spent 1 or 2 years in freshwater before smoltifying. Those fish becoming smolts at the end of 1 year were the most numerous (54%). The majority of the fish sampled were spring fish (82.4%). Very few summer fish were identified and those found were mainly grilse. The high proportion of spring fish in the sample is due to the high proportion of rod-caught fish. Probably a complete census over the year would show a larger proportion of grilse and summer fish as these are not subject to heavy rod-fishing the season being closed at the beginning of June. The relationship between sea age and river age and the influence of freshwater life upon the sea life were tested in four rivers. It seems probable that sea life depends chiefly on the river and the year of smoltification rather than on the freshwater stage. The biometric characteristics of Brittany salmon were compared with data from some foreign rivers. The angling exploitation of the spring Atlantic salmon in Brittany and the lack of data about summer migrations are discussed in regard to the future of this stock.     

Return migration of adult Atlantic salmon, Salmo salar, in relation to water diverted through a power station

Abstract  The migration of Atlantic salmon, Salmo salar L., returning to the River Suldalslågen, Norway, was studied in relation to redirection of freshwater flow through a power station. The outlet of the power station is situated in the Hylsfjord, a fjord adjacent to the river mouth. Seventy-two salmon were tagged with acoustic transmitters, released in the outer part of the fjord system and automatically recorded when entering the Hylsfjord or the river. Data were collected during one period when the power station was running and two periods when the power station was closed. The release of water from the power station did not greatly attract the salmon during their return migration. Proportions of salmon entering the river or time from release to entering the river did not differ among salmon tagged in the different periods. The salmon were recorded in the Hylsfjord both when the power station was running and closed and there were no differences in number of times, number of days or hours recorded in the Hylsfjord among salmon tagged in the three periods. The only significant difference found among periods was duration of continuous stays in the inner part of the Hylsfjord. This may indicate a slight attraction to the freshwater release, but the difference seems small (1.8 vs. 0.7 h) compared with the time the fish stayed in the fjord system before entering the river (16–85 days).     

Timing of spawning in cultured and wild Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in the River Vosso, Norway

Spawning time and size of wild and nonnative cultured female Atlantic salmon (Salmo salar L.) were studied in the River Vosso, Norway. Cultured immigrants were smaller, and peak spawning occurred 21 and 26 days earlier relative to wild salmon in 1991 and 1992, respectively. It was calculated that hatching and initial feeding of offspring of cultured females peaked 12 and 9 days earlier in spring 1992 and 19 and 8 days earlier in spring 1993 relative to offspring of wild females. Spawning time of the cultured salmon is similar to most Norwegian salmon populations and to cultured fish in other streams. In the River Vosso it also overlaps with that of brown trout (Salmo trutta L.), which may increase hybridization. The early time of breeding in nonnative fish indicates local adaptation in this trait in wild salmon. The consequences of early breeding of cultured fish are unpredictable in relation to spring temperatures but probably reduce their relative breeding success. The smaller size may also reduce the success of cultured females.     

Temporal and spatial responses of British Columbia steelhead (Oncorhynchus mykiss) populations to ocean climate shifts

The pattern of temporal change in recruitment of steelhead trout ( Oncorhynchus mykiss ) entering the ocean between 1963 and 1990 was geographically coherent in all regions of British Columbia. A major increase in recruitment was evident for smolts entering the ocean after 1977. Subsequently, an out-of-phase response occurred after 1990, indicating that the effect of a possible 1990 regime shift had both temporal and geographical structure. Steelhead entering northern regions had increasing recruitment, while steelhead entering southern BC coastal regions had sharply decreasing recruitment. The evidence clearly indicates that the overall recruitment response since 1977 was primarily shaped by changes in marine (not freshwater) survival. Similar sudden changes in adult recruitment also appear to be occurring for other species of Pacific salmon in BC and Oregon, such as coho ( O. kisutch ), which appear to occur suddenly and show considerable persistence. A possible explanation for the change is that ocean productivity declined in coastal regions of southern BC after 1990, reducing the marine growth of juvenile salmon. The Bakun upwelling index shows a pattern of geographical coherence along the west coast of North America that could in principle explain the observed pattern of changes in recruitment. However, no evidence for a temporal shift in this index occurring around 1977 and 1990 is apparent. The reason for the sudden and persistent decline in ocean survival is therefore uncertain.     

Comparative feeding, growth and movements of Atlantic salmon (Salmo salar) parr from riverine and estuarine environments

Abstract– The diet composition, movcments and growth of Atlantic salmon parr rearing in the estuary of Western Arm Brook, Newfoundland were compared with those of parr from riverine habitats over 2 years. Estuarine parr consumed a variety of prey, including many freshwater taxa (mainly insects), which indicated a dependence on freshwater drift from the river. Prey of estuarine origin (amphipods and sticklebacks) were increasingly consumed between spring and autumn. Prey volume per fish and number of prey per fish increased significantly for estuarine parr between spring and autumn, suggesting an improvement in food availability. Riverine parr, however, realized a general decrease in both parameters between spring and autumn. The recapture of 16% ( n = 131) of the 829 parr marked in the estuary in 1987 and 1988 indicated a directed movement toward the head of the estuary and river mouth, as also suggested by the diet analysis. Parr from outer estuary sites were very mobile compared with parr from the estuary site closest to the river mouth, which behaved more like parr in the river proper in displaying strong site fidelity. Movement patterns of parr were primarily along the shoreline. Individual growth rates were highly variable in both environments but especially in the estuary. The mean growth of estuarine parr was 0.23 mm. d⁻¹ between May and October with some evidence of fastest growth having occurred in late spring and early summer (approx. 0.4 mm. d⁻¹); mean growth rate of riverine parr was slower, at 0.12 mm. d⁻¹. The results are discussed in the context that estuarine rearing by salmon parr represents an alternative life-history tactic for the species in river systems in eastern Canada.     

Marine and freshwater climatic factors affecting interannual variation in the timing of return migration to fresh water of sockeye salmon (Oncorhynchus nerka)

Interannual variation in the timing of the return migration to fresh water of adult sockeye salmon, Oncorhynchus nerka, from 46 populations throughout the species North American range was examined in a broad analysis of how timing patterns are affected by marine and freshwater conditions. Migration timing data (measured at various points along the migration, including just prior to freshwater entry, just after freshwater entry, and near the spawning grounds) were examined for correlations with sea‐surface temperatures (SST) prior to migration and to freshwater temperatures and flows during migration. Following a spring–summer period with warm SST, populations from southwestern Alaska tended to return early, Fraser River populations returned late, and populations from other regions showed no consistent patterns. Similarities between interannual timing of both nearby and distant populations indicated the presence of common or coincidental influences on timing. When riverine conditions related to timing, high flows and low temperatures were associated with late migrations, low flows and high temperatures were associated with early migrations. However, even counting stations at upriver locations showed correlations with SST. Notwithstanding some inconsistencies among the many populations examined and the indirect nature of the inferences, the results supported the hypotheses that (i) interannual variations in salmon distributions at sea reflect temperature conditions, and (ii) the date when salmon initiate homeward migration is a population‐specific trait, largely unaffected by the fish's location at sea.     

Importance of the River Teviot to Atlantic salmon, Salmo salar, rod catches in the River Tweed, Scotland

Abstract  The body mass distributions and variations in abundance of the spring and autumn catches of Atlantic salmon, Salmo salar L., were compared between fisheries above and below the confluence of the rivers Tweed and Teviot, Scotland. Significant differences between the distributions were found over three periods, one in spring and two in autumn, when salmon catches were high. Correlations were found between abundance trends for periods when distributions were similar or dissimilar. Abundance of salmon returning to the River Teviot was proportional to the main river. However, its population structure differed when abundances were high, suggesting different survival strategies. It appears that changes in the numbers returning to the river were resultant of changes in the marine rather than freshwater environment.     

Sea lice infestation rates on wild and escaped farmed Atlantic salmon (Salmo salar L.) entering the Magaguadavic River, New Brunswick

A monitoring program for the prevalence and intensity of sea lice infestations of wild and escaped farmed salmon has been underway on the Magaguadavic River since 1992. Fish are screened in a fish ladder trap located in freshwater a short distance above the head of tide. No trends with time were evident in observed sea lice burdens, and in all years the majority of salmon, both wild and escapees, had no or low levels of infestation with sea lice. In the spring of 2002, 23 landlocked salmon moving to sea from the Magaguadavic River were acoustically tagged. Two fish returned to the river after a brief period of residence in Passamaquoddy Bay, with significant dermal damage from sea lice. These fish were tracked to areas close to commercial salmon farms.     

东海区太平洋褶柔鱼生殖群体结构特征的季节差异

依据1997~1999年东海区春、夏、秋3个季节的底拖网资料,分析了东海区太平洋褶柔鱼生殖群体的性别组成、性腺成熟度和初次性成熟胴长等群体结构特征。结果表明:在东海区春、夏、秋三季均存在太平洋褶柔鱼的生殖群体。各季节生殖群体的雌雄比例均不符合1∶1的关系(P<0.05),雌性比例小于雄性。生殖群体中性成熟个体胴长的季节性变化较为明显,雌、雄平均胴长均以秋季最大,夏季最小。雌性个体的平均胴长均显著大于雄性。各季节太平洋褶柔鱼生殖群体中胴长与体重关系的性别差异极显著(P<0.01)。此外,不同季节雌、雄太平洋褶柔鱼的初次性成熟胴长差异较大,雌性为:春季223.4 mm、夏季170.4 mm、秋季202.3 mm;雄性为:春季174.0 mm、夏季164.3 mm、秋季165.3 mm。雄性初次性成熟胴长小于雌性,夏季雌、雄初次成熟胴长均小于春、秋季。依据春季生殖群体的胴长范围、初次性成熟胴长等群体结构特征推测,在东海区可能存在着小规模的春生群。     

Incidence of escaped farmed salmon, Salmo salar L., in commercial salmon catches and fresh water in Northern Ireland

External morphological characteristics were used to identify escaped farmed Atlantic salmon, Salmo salar L., in a coastal salmon fishery in County Antrim, Northern Ireland during four fishing seasons and at an adjacent freshwater location (R. Bush) during a 5-year period. Out of a total of 36 326 adult salmon examined in the fishery, 883 (2.4%) were identified as having escaped from sea cages. Annual average values ranged from 0.26% to 4.04% of the fish caught. Occurrence of escapees entering an adult trap in fresh water averaged 0.88%, with a range of 0.13–2.62%, depending on year. No correlation between presence in the marine fishery and in fresh water was evident, the latter year-round figures probably being more indicative of presence of escapees in spawning stocks. Entry to fresh water was significantly later on average for escaped farmed salmon, compared with wild salmon.     

Immunoreactive somatolactin cells in the pituitary of young,migrating, spawning and spent chinook salmon,Oncorhynchus tshawytscha

Immunocytochemical techniques using an antiserum to cod somatolactin (SL) demonstrated the presence of SL cells in the intermediate lobe of the pituitary in Oncorhynchus tshawytscha. The cells were small in yearling fish. Two groups of maturing fish were studied. In the spring run salmon collected in April and May during the upstream migration, the SL cells appeared stimulated. In September, during spawning, SL cell stimulation was maximal with indices of hypertrophy and degranulation often more marked in females than in males. In the other group, salmon of the fall run collected in the Pacific Ocean in August had well developed gonads, large gonadotropes and abundant SL cells. In spawning salmon (September) the SL cells were stimulated, mainly in females. However, the final stimulation was less intense than in spring run spawning fish. The SL cells were smaller, without evident granule release, but still abundant in spent salmon of the fall run caught at the end of November. Various factors (time spent in rivers before spawning, starvation, decalcification, stress, hypothalamic influences) were considered which might explain differences between spring and fall run salmon. These observations suggest that SL may play a role in the control of gonadal maturation in chinook salmon as it may also do in sockeye and chum salmon previously studied, and that SL cells may be sensitive to the ambient salinity.     

Effects of salinity on sexual maturity and reproduction of Poecilia velifera

Poecilia velifera is a popular fish in freshwater aquarism that naturally inhabits aquatic habitats with a wide range of salinities. Nonetheless, the effects of different salinities on the reproductive success and sex ratio of the species remain unknown. Male sex characters, sex ratio and reproductive success of P. velifera were evaluated by maintaining 160 juveniles (0.078 ± 0.011 g) in four different salinities (0; 12; 24; 36 g/L), with four replicates. The only modification observed in males was the formation of a copulatory organ from the anal fin, which was used to distinguish them from females. Timing of the formation of the male copulatory organ, and the weight and total length of males when it occurred, were recorded. Twenty‐eight fish from each treatment were euthanized after 150 day to examine the gonads and confirm sex. Eight females and four males from each treatment were then kept in their respective salinity treatments for 65 days to examine the effects of salinity on reproduction. Males were kept with females in the different treatments for 15 days, at which point they were removed. Salinity was negatively correlated with male weight and length. Salinity also affected the sex ratio, with the percentages of males and females being 32.5 and 67.5%, and 27.5 and 72.5% in the salinities of 24 and 36 g of salt/L, respectively. Fifty percent of the females kept in freshwater reproduced, while there was no reproduction in the other treatments. The maintenance of P. velifera in freshwater promoted greater reproductive success and precocity, as well as larger males.     

Density‐dependent effects of eastern Kamchatka pink salmon (Oncorhynchus gorbuscha) and Japanese chum salmon (O. keta) on age‐specific growth of western Alaska chum salmon

Hatcheries release >4.5 billion juvenile Pacific salmon (Oncorhynchus spp.) into the North Pacific Ocean annually, raising concerns about competition with wild salmon populations. We used retrospective scale analysis to investigate how the growth of chum salmon (O. keta) from western Alaska is affected by the abundance of chum salmon from Japanese hatcheries and wild pink salmon (O. gorbuscha) from the Russian Far East. Over nearly five decades, the growth of Kuskokwim River chum salmon was negatively correlated with the abundance of Japanese hatchery chum salmon after accounting for the effects of sex and spring/summer sea‐surface temperature in the Bering Sea. An effect of wild eastern Kamchatka pink salmon abundance on the growth of Kuskokwim River salmon was detectable but modest compared to the intraspecific competitive effect. A decrease in Japanese hatchery chum salmon releases in 2011–2013 was not associated with increased growth of Bering Sea chum salmon. However, the abundance of wild chum salmon from the Russian Far East increased during that time, possibly obscuring reduced competition with hatchery chum salmon. Our results support previous evidence that chum salmon are affected by intraspecific competition, and to a lesser extent interspecific competition, in the North Pacific, underscoring that the effects of salmon hatchery production transcend national boundaries.     

Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life histories

Abstract – Among the species in the family Salmonidae, those represented by the genera Salmo, Salvelinus, and Oncorhynchus (subfamily Salmoninae) are the most studied. Here, various aspects of phenotypic and life‐history variation of Atlantic salmon Salmo salar L., brown trout Salmo trutta L., and Arctic charr Salvelinus alpinus (L.) are reviewed. While many strategies and tactics are commonly used by these species, there are also differences in their ecology and population dynamics that result in a variety of interesting and diverse topics that are challenging for future research. Atlantic salmon display considerable phenotypic plasticity and variability in life‐history characters ranging from fully freshwater resident forms, where females can mature at approximately 10 cm in length, to anadromous populations characterised by 3–5 sea‐winter (5SW) salmon. Even within simple 1SW populations, 20 or more spawning life‐history types can be identified. Juveniles in freshwater can use both fluvial and lacustrine habitats for rearing, and while most smolts migrate to sea during the spring, fall migrations occur in some populations. At sea, some salmon undertake extensive oceanic migrations while other populations stay within the geographical confines of areas such as the Baltic Sea. At the other extreme are those that reside in estuaries and return to freshwater to spawn after spending only a few months at sea. The review of information on the diversity of life‐history forms is related to conservation aspects associated with Atlantic salmon populations and current trends in abundance and survival. Brown trout is indigenous to Europe, North Africa and western Asia, but was introduced into at least 24 countries outside Europe and now has a world‐wide distribution. It exploits both fresh and salt waters for feeding and spawning (brackish), and populations are often partially migratory. One part of the population leaves and feeds elsewhere, while another part stays as residents. In large, complex systems, the species is polymorphic with different size morphs in the various parts of the habitat. Brown trout feed close to the surface and near shore, but large individuals may move far offshore. The species exhibits ontogenetic niche shifts partly related to size and partly to developmental rate. They switch when the amount of surplus energy available for growth becomes small with fast growers being younger and smaller fish than slow growers. Brown trout is an opportunistic carnivore, but individuals specialise at least temporarily on particular food items; insect larvae are important for the young in streams, while littoral epibenthos in lakes and fish are most important for large trout. The sexes differ in resource use and size. Females are more inclined than males to become migratory and feed in pelagic waters. Males exploit running water, near‐shore and surface waters more than females. Therefore, females feed more on zooplankton and exhibit a more uniform phenotype than males. The Arctic charr is the northernmost freshwater fish on earth, with a circumpolar distribution in the Holarctic that matches the last glaciation. Recent mtDNA studies indicate that there are five phylogeographic lineages (Atlantic, Arctic, Bering, Siberian and Acadian) that may be of Pleistocene origin. Phenotypic expression and ecology are more variable in charr than in most fish. Weights at maturation range from 3 g to 12 kg. Population differences in morphology and coloration are large and can have some genetic basis. Charr live in streams, at sea and in all habitats of oligotrophic lakes, including very deep areas. Ontogenetic habitat shifts between lacustrine habitats are common. The charr feed on all major prey types of streams, lakes and near‐shore marine habitats, but has high niche flexibility in competition. Cannibalism is expressed in several cases, and can be important for developing and maintaining bimodal size distributions. Anadromy is found in the northern part of its range and involves about 40, but sometimes more days in the sea. All charr overwinter in freshwater. Partial migration is common, but the degree of anadromy varies greatly among populations. The food at sea includes zooplankton and pelagic fish, but also epibenthos. Polymorphism and sympatric morphs are much studied. As a prominent fish of glaciated lakes, charr is an important species for studying ecological speciation by the combination of field studies and experiments, particularly in the fields of morphometric heterochrony and comparative behaviour.     

Efficacy of manual removal and ivermectin gavage for control of Salmincola californiensis (Wilson) infestation of chinook salmon, Oncorhynchus tshawytscha (Walbaum), captive broodstocks

Captive broodstocks of spring chinook salmon, Oncorhynchus tshawytscha , were initiated from collections of naturally produced parr from the Lemhi River, a tributary of the Salmon River, ID, USA. These fish were subsequently demonstrated to be infested with the copepod parasite Salmincola californiensis . The initial prevalence of visible adult parasites for 4 years of observations made shortly after collection varied from 19.7 to 71.6%. Both the prevalence and intensity of the infestation increased in the freshwater culture of these fish. Manual removal was initiated as a means of control and practiced at monthly intervals. The number of Salmincola removed decreased in the ensuing 5 months, but the prevalence was not greatly affected. Ivermectin (22,23 dihydroavermectin), was diluted with saline and delivered by gavage at the rate of 0.20 mg kg⁻¹ body weight when the groups were being handled for the manual removal of parasites. Either two or three ivermectin treatments were given to four broodstocks of chinook salmon depending on the severity of the infestation and on the extent of gill pathology. The combination of manual removal and ivermectin gavage eliminated live Salmincola and resolved all associated necrosis of the gill tissues. There was no trend to indicate that individual chinook salmon possessed a natural resistance to reinfestation.     

Nomads no more: early juvenile coho salmon migrants contribute to the adult return

The downstream movement of coho salmon fry and parr in the fall, as distinct from the spring migration of smolts, has been well documented across the range of the species. In many cases, these fish overwinter in freshwater, but they sometimes enter marine waters. It has long been assumed that these latter fish did not survive to return as adults and were ‘surplus’ to the stream's carrying capacity. From 2004 to 2010, we passive integrated transponder tagged 25,981 juvenile coho salmon in three streams in Washington State to determine their movement, survival and the contribution of various juvenile life histories to the adult escapement. We detected 86 returning adults, of which 32 originated from fall/winter migrants. Half of these fall/winter migrants spent ~1 year in the marine environment, while the other half spent ~2 years. In addition, the median return date for fall/winter migrants was 16 days later than spring migrants. Our results indicated that traditional methods of spring‐only smolt enumeration may underestimate juvenile survival and total smolt production, and also overestimate spring smolt‐to‐adult return (SAR). These are important considerations for coho salmon life cycle models that assume juvenile coho salmon have a fixed life history or use traditional parr‐to‐smolt and SAR rates.     

Female-biased mortality rate and sexual size dimorphism of migratory masu salmon, Oncorhynchus masou

Abstract –  We examined whether mortality and growth during the migration phase (the lacustrine phase after smolting) differ between sexes in migratory (lake-run) masu salmon ( Oncorhynchus masou ) in a lacustrine population, northern Hokkaido, Japan. The sex ratio of 1+ smolts was more skewed to females than that of the returning adults in three annual cohorts examined, indicating that females have a higher mortality rate during the migration phase. Although there was no difference in smolt length between sexes, female adults were larger in body length than males of the same age: female-biased sexual size dimorphism (SSD) occurs. We suppose that breeding selection favouring a larger body size for females than for males in this population probably requires that females undertake more intensive foraging behaviour with its greater inherent risks but faster growth rates during the migration phase. It therefore seems to be likely that the selection is the ultimate cause of the female-biased mortality rate and SSD.     

Distribution and feeding of juvenile Pacific salmon in freshwater tidal creeks of the lower Fraser River, British Columbia

Abstract This study examined juvenile salmonid use of a freshwater tidal creek system draining a wetland on the floodplain of the lower Fraser River, British Columbia, Canada. Chum, Oncorhynchus keta (Walbaum), chinook, O. tshawytscha (Walbaum), and sockeye, O. nerka (Walbaum), salmon fry were abundant in the tidal creeks in spring. The fry were found in non-natal habitat up to 1.5 km from the main channel of the river. The salmon fry ate dipteran adults, larvae and pupae, cyclopoid and harpacticoid copepods, and Collembola. Mysids Neomysis mercedis Holmes (Walbaum), and amphipods, Crangonyx richmondensis occidentalis (Hubricht and Harrison), were also consumed. The upper reaches of an undisturbed creek were the winter rearing habitat for presmolt coho salmon, O. kisutch (Walbaum), where this species ate dipteran pupae and larvae as well as a freshwater isopod, Asellus communis Say (Walbaum).     

Influence of river conditions during seaward migration and ocean conditions on survival rates of Snake River Chinook salmon and steelhead

Petrosky CE, Schaller HA. Influence of river conditions during seaward migration and ocean conditions on survival rates of Snake River Chinook salmon and steelhead.
Ecology of Freshwater Fish 2010: 19: 520–536. © 2010 John Wiley & Sons A/S Abstract – Improved understanding of the relative influence of ocean and freshwater factors on survival of at‐risk anadromous fish populations is critical to success of conservation and recovery efforts. Abundance and smolt to adult survival rates of Snake River Chinook salmon and steelhead decreased dramatically coincident with construction of hydropower dams in the 1970s. However, separating the influence of ocean and freshwater conditions is difficult because of possible confounding factors. We used long time‐series of smolt to adult survival rates for Chinook salmon and steelhead to estimate first year ocean survival rates. We constructed multiple regression models that explained the survival rate patterns using environmental indices for ocean conditions and in‐river conditions experienced during seaward migration. Survival rates during the smolt to adult and first year ocean life stages for both species were associated with both ocean and river conditions. Best‐fit, simplest models indicate that lower survival rates for Chinook salmon are associated with warmer ocean conditions, reduced upwelling in the spring, and with slower river velocity during the smolt migration or multiple passages through powerhouses at dams. Similarly, lower survival rates for steelhead are associated with warmer ocean conditions, reduced upwelling in the spring, and with slower river velocity and warmer river temperatures. Given projections for warming ocean conditions, a precautionary management approach should focus on improving in‐river migration conditions by increasing water velocity, relying on increased spill, or other actions that reduce delay of smolts through the river corridor during their seaward migration.     

Hematological parameters and phagocytic activity in fat snook (Centropomus parallelus): Seasonal variation, sex and gonadal maturation

The objective of this work was to determine hematological parameters and the phagocytic capacity of peritoneal macrophages of the fat snook related to sex, stage of gonadal maturation and seasonal cycle. The hematological results did not show significant differences between males and females. With respect to stage of gonadal maturation, only erythrocytes numbers (RBC), in females, was found to be significantly elevated in stage III (maturing) and decreased in V (spent). An analysis of the results of the erythrocyte and leukocyte series, thrombocytes and phagocytic activity related to sex and seasonal cycle showed statistically significant differences: a) hematocrit (Ht) and hemoglobin concentration (Hb) were elevated in the spring and low in the winter in males; b) mean corpuscular volume (MCV) was high in the spring and summer and low in the fall in both sexes; c) thrombocytes numbers were elevated in the fall and low in the other seasons in females; d) phagocytic capacity (PC) and phagocytic index (PI) were higher in the summer and lower in the fall in females. The results showed that spring and summer correspond to seasons of the year for better hematological and phagocytic responses for survival of the fat snook in its natural habitat. The parameters studied could be utilized for evaluation of the health status fat snook in its own habitat or in captivity.