A comparative tissue distribution study of oxytetracycline in rainbow trout, Oncorhynchus mykiss (Walbaum), and chinook salmon, Oncorhynchus tshawytscha (Walbaum)

Oxytetracycline (OTC), a broad-spectrum antibiotic, is used widely to treat bacterial diseases in farmed fish. In the present study, the time course of OTC concentrations in freshwater rainbow trout, Oncorhynchus mykiss (Walbaum), and seawater chinook salmon, Oncorhynchus tshawytscha (Walbaum), were compared, tissue by tissue, after receiving a bolus dose of the antibiotic (5 mg kg^–1 or 50 mg kg^–1) intra-arterially (i.a.). The OTC concentration–time profiles of rainbow trout tissues were found to be very similar to those of the corresponding tissues in chinook salmon. Therefore, neither water salinity nor fish species seemed to play an important role in the disposition and elimination of OTC in these salmonids. In a separate experiment, rainbow trout were implanted surgically with a urinary cannula and received a single dose of OTC (50 mg kg^–1) i.a. Urine was collected from the cannula daily for 13 days. The amount of OTC excreted into the bile was found to be larger than that eliminated by the urine. These results show the similarity of OTC pharmacokinetics in freshwater rainbow trout and seawater chinook salmon and render support in using a single fish species to study the pharmacokinetics of a drug for other species in the same taxon.     

Copepods and salmon: characterizing the spatial distribution of juvenile salmon along the Washington and Oregon coast,USA

Yearling Chinook (Oncorhynchus tshawytscha) and coho salmon (Oncorhynchus kisutch) were sampled concurrently with physical variables (temperature, salinity, depth) and biological variables (chlorophyll a concentration and copepod abundance) along the Washington and Oregon coast in June 1998–2008. Copepod species were divided into four different groups based on their water‐type affinities: cold neritic, subarctic oceanic, warm neritic, and warm oceanic. Generalized linear mixed models were used to quantify the relationship between the abundance of these four different copepod groups and the abundance of juvenile salmon. The relationships between juvenile salmon and different copepod groups were further validated using regression analysis of annual mean juvenile salmon abundance versus the mean abundance of the copepod groups. Yearling Chinook salmon abundance was negatively correlated with warm oceanic copepods, warm neritic copepods, and bottom depth, and positively correlated with cold neritic copepods, subarctic copepods, and chlorophyll a concentration. The selected habitat variables explained 67% of the variation in yearling Chinook abundance. Yearling coho salmon abundance was negatively correlated with warm oceanic copepods, warm neritic copepods, and bottom depth, and positively correlated with temperature. The selected habitat variables explained 40% of the variation in yearling coho abundance. Results suggest that copepod communities can be used to characterize spatio‐temporal patterns of abundance of juvenile salmon, i.e., large‐scale interannual variations in ocean conditions (warm versus cold years) and inshore‐offshore (cross‐shelf) gradients in the abundance of juvenile salmon can be characterized by differences in the abundance of copepod species with various water mass affinities.     

Development of a Piscirickettsia salmonis immersion challenge model to investigate the comparative susceptibility of three salmon species

Piscirickettsia salmonis, the aetiological agent of salmonid rickettsial septicaemia (SRS), is a global pathogen of wild and cultured marine salmonids. Here, we describe the development and application of a reproducible, standardized immersion challenge model to induce clinical SRS in juvenile pink (Oncorhynchus gorbuscha), Atlantic (Salmo salar) and sockeye salmon (O. nerka). Following a 1‐hr immersion in 10⁵ colony‐forming units/ml, cumulative mortality in Atlantic salmon was 63.2% while mortality in sockeye salmon was 10%. Prevalence and levels of the bacterium in kidney prior to onset of mortality were lower in sockeye compared with Atlantic or pink salmon. The timing and magnitude of bacterial shedding were estimated from water samples collected during the exposure trials. Shedding was estimated to be 82‐fold higher in Atlantic salmon as compared to sockeye salmon and peaked in the Atlantic salmon trial at 36 d post‐immersion. These data suggest sockeye salmon are less susceptible to P. salmonis than Atlantic or pink salmon. Finally, skin lesions were observed on infected fish during all trials, often in the absence of detectable infection in kidney. As a result, we hypothesize that skin is the primary point of entry for P. salmonis during the immersion challenge.     

A single‐dose pharmacokinetic study of emamectin benzoate in cod,Gadus morhua L., held in sea water at 9 °C

The pharmacokinetic profile of the antiparasitic agent emamectin benzoate was studied in plasma after intravenous (i.v.) injection and in plasma, muscle and skin following oral (p.o.) administration to cod, Gadus morhua, held in sea water at 9 °C and weighing 100–200 g. Following i.v. injection, the plasma drug concentration‐time profile showed two distinct phases. The plasma distribution half‐life (t_1/2α) was estimated as 2.5 h, the elimination half‐life (t_1/2β) as 216 h, the total body clearance (Cl_T) as 0.0059 L kg^?1 h^?1 and mean residence time (MRT) as 385 h. The volume of distribution at steady state, V_d(ss), was calculated to be 1.839 L kg^?1. Following p.o. administration the peak plasma concentration (C_max) was 15 ng mL^?1, the time to peak plasma concentration (T_max) was 89 h and t_1/2β was 180 h. The highest concentration in muscle (21 ng g^?1) was measured after 7 days and t_1/2β was calculated to be 247 h. For skin, a peak concentration of 28 ng g^?1 at 3 days was observed and a t_1/2β of 235 h was determined. The bioavailability following p.o. administration was calculated to be 38%.     

Use of microsatellite DNA and amplified fragment length polymorphism for Cherry salmon (Oncorhynchus masou) complex identification

Formosa landlocked salmon (Oncorhynchus masou formosanus), an endemic, critically endangered subspecies of Cherry salmon (Oncorhynchus masou) complex, is only found in Taiwan. Because the eyed eggs and ungutted carcasses of Pacific salmons (genus Oncorhynchus) are imported for aquaculture and food to Taiwan from overseas every year, the requirement for preventing illegal trade or accidental commercial imports to avoid unwanted fish from contaminating the gene pool of Formosa landlocked salmon and infect them with diseases is critical for the conservation of Formosa landlocked salmon. Traditional morphology‐based species identification is impossible for salmon eggs and larvae that lack clearly defined morphological features. In the present study, the genetic differences among four subspecies (Oncorhynchus masou ishikawae, O. masou subsp., Oncorhynchus masou masou and O. masou formosanus) of Cherry salmon complex were determined from microsatellite DNA and amplified fragment length polymorphism analyses. We successfully generated a genetic marker to aid traditional taxonomy and investigate the integrity of the current taxonomic status among members of Cherry salmon complex. Use of molecular markers, in combination with traditional morphological identification, is a promising tool for identifying four closely related subspecies of Cherry salmon complex.     

Effect of route of administration and carrier on bioavailability and kinetics of astaxanthin in Atlantic salmon Salmo salar L.

This study examined astaxanthin bioavailability and kinetics in adult Atlantic salmon Salmo salar L., following two different routes of astaxanthin administration (oral vs. intraperitoneal (i.p.) injection) using two different carriers of the pigment (gelatin vs. sesame oil). The dorsal aorta of adult Atlantic salmon (mean initial weight 950 g) was cannulated. The fish received a single dose of astaxanthin (572 μg kg^?1) in sesame oil or (514 μg kg^?1) in gelatin via the oral or i.p. route. Plasma was sampled regularly up to 72 h post oral administration and up to 510 h post i.p. injection. The astaxanthin concentration–time curves from plasma were best fit to a one‐compartment pharmacokinetic model for each of the four treatments. The gelatin carrier resulted in higher availability of astaxanthin compared to the sesame oil carrier. The bioavailability for astaxanthin in sesame oil was only 38.7% of that in gelatin by i.p. injection, and only 53.5% of that in gelatin by oral administration. Higher availability of astaxanthin was observed when i.p. injection was used compared to oral administration. The bioavailability for astaxanthin administered orally was only 12% of that by i.p. injection in sesame oil, and only 8.7% of that by i.p. injection in gelatin.     

Competitive interactions among multiple non‐native salmonids and two populations of Atlantic salmon

Competitive interactions with non‐native species can have negative impacts on the conservation of native species, resulting in chronic stress and reduced survival. Here, juvenile Atlantic salmon (Salmo salar) from two allopatric populations (Sebago and LaHave) that are being used for reintroduction into Lake Ontario were placed into semi‐natural stream tanks with four non‐native salmonid competitors that are established in Ontario streams: brown trout (S. trutta), rainbow trout (Oncorhynchus mykiss), Chinook salmon (O. tshawytscha) and coho salmon (O. kisutch). Brown trout and rainbow trout reduced the survival and fitness‐related traits of Atlantic salmon, whereas Chinook salmon and coho salmon had no impact on these traits. These data support theories on ecological niche overlap and link differences in observed aggression levels with competitive outcomes. Measurements of circulating hormones indicated that the Atlantic salmon were not chronically stressed nor had a change in social status at the 10‐month time point in the semi‐natural stream tanks. Additionally, the Sebago population was better able to coexist with the non‐native salmonids than the LaHave population. Certain populations of Atlantic salmon may thus be more suitable for some environments of the juvenile stream phase for the reintroduction into Lake Ontario.     

Covariation between the average lengths of mature coho (Oncorhynchus kisutch) and Chinook salmon (O. tshawytscha) and the ocean environment

We used the average fork length of age‐3 returning coho (Oncorhynchus kisutch) and age‐3 ocean‐type and age‐4 stream‐type Chinook (Oncorhynchus tshawytscha) salmon along the northeast Pacific coast to assess the covariability between established oceanic environmental indices and growth. These indices included the Multivariate El Niño‐Southern Oscillation Index (MEI), Pacific Decadal Oscillation (PDO), Northern Oscillation Index, and Aleutian Low Pressure Index. Washington, Oregon, and California (WOC) salmon sizes were negatively correlated with the MEI values indicating that ultimate fish size was affected negatively by El Niño‐like events. Further, we show that the growth trajectory of WOC salmon was set following the first ocean winter. Returning ocean‐type British Columbia‐Puget Sound Chinook salmon average fork length was positively correlated with the MEI values during the summer and autumn of return year, which was possibly a result of a shallower mixed layer and improved food‐web productivity of subarctic Pacific waters. Size variation of coho salmon stocks south of Alaska was synchronous and negatively correlated with warm conditions (positive PDO) and weak North Pacific high pressure during ocean residence.     

Spatial distribution of ocean habitat of yearling Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon off Washington and Oregon,USA

We determined the habitat usage and habitat connectivity of juvenile Chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon in continental shelf waters off Washington and Oregon, based on samples collected every June for 9 yr (1998–2006). Habitat usage and connectivity were evaluated using SeaWiFS satellite‐derived chlorophyll a data and water depth. Logistic regression models were developed for both species, and habitats were first classified using a threshold value estimated from a receiver operating characteristic curve. A Bernoulli random process using catch probabilities from observed data, i.e. the frequency of occurrence of a fish divided by the number of times a station was surveyed, was applied to reclassify stations. Zero‐catch probabilities of yearling Chinook and yearling coho salmon decreased with increases in chlorophyll a concentration, and with decreases in water depth. From 1998 to 2006, ～ 47% of stations surveyed were classified as unfavorable habitat for yearling Chinook salmon and ～ 53% for yearling coho salmon. Potentially favorable habitat varied among years and ranged from 9 856 to 15 120 km² (Chinook) and from 14 800 to 16 736 km² (coho). For both species, the smallest habitat area occurred in 1998, an El Niño year. Favorable habitats for yearling Chinook salmon were more isolated in 1998 and 2005 than in other years. Both species had larger and more continuous favorable habitat areas along the Washington coast than along the Oregon coast. The favorable habitats were also larger and more continuous nearshore than offshore for both species. Further investigations on large‐scale transport, mesoscale physical features, and prey and predator availability in the study area are necessary to explain the spatial arrangement of juvenile salmon habitats in continental shelf waters.     

An outbreak of acute disease and mortality in Atlantic salmon (Salmo salar) post‐smolts in Norway caused by Tenacibaculum dicentrarchi

An outbreak of disease characterized by skin ulcers, fin rot and mortality was observed a few days after the transfer of Atlantic salmon (Salmo salar) from a freshwater smolt production facility to a land‐based seawater post‐smolt site. Dead and moribund fish had severe skin and muscle ulcers, often 2–6 cm wide, particularly caudal to the pectoral fins. Microscopic examination of smears from ulcers and head kidney identified long, slender Gram‐negative rods. Histopathological analysis revealed abundance of long, slender Tenacibaculum‐like bacteria in ulcers and affected fins. Genetic characterization using multilocus sequence analysis (MLSA) of seven housekeeping genes, including atpA, dnaK, glyA, gyrB, infB, rlmN and tgt, revealed that the isolates obtained during the outbreak were all clustered with the Tenacibaculum dicentrarchi‐type strain (USC39/09^T) from Spain. Two bath challenge experiments with Atlantic salmon and an isolate of T. dicentrarchi from the outbreak were performed. No disease or mortality was observed in the first trial. In the second trial with a higher challenge dose of T. dicentrarchi and longer challenge time, we got 100% mortality within 48 hr. This is the first reported outbreak of disease caused by T. dicentrarchi in Norwegian farmed Atlantic salmon.     

Hepatopancreatic and muscular distribution of oxytetracycline antibiotics in farmed pacific white shrimp (Penaeus vannamei): a physiological‐based pharmacokinetic model approach

Oxytetracycline (OTC) pharmacokinetic models previously used to investigate Penaeus vannamei have not addressed the specific problems related to drug distribution/disposition in particular tissues. This study aimed to provide an insight into OTC kinetics in the hepatopancreas and muscle based on a physiological model approach. Adult male P. vannamei at the C‐D₀ inter‐moulting stage were randomly assigned to intra‐sinus and oral administrations. In the intra‐sinus group, shrimps were dosed via the ventral sinus at an OTC level of 10.0 μg g^?1 body weight, while in the oral one, they were force fed at a dose level of 50.2 μg g^?1. The medicated animals were sampled at various time intervals until 170 h after dosing. Haemolymph, muscle and hepatopancreas samples were taken and OTC levels were determined using the validated HPLC method. A model focused on the hepatopancreas and muscle was developed. Oxytetracycline pharmacokinetic profiles in particular tissues were fitted into the model with an R² of between 0.6568 and 0.9904. Oxytetracycline muscular distributions were essentially identical for both groups and the drug did not accumulate in muscle. The distributions in the hepatopancreas for both groups were extensive, whereas that for oral administration was approximately 2.3 times greater than that for the intra‐sinus one. It was demonstrated that hepatopancreatic OTC may undergo significant first‐pass elimination with non‐linear kinetics.     

Ecological processes influencing mortality of juvenile pink salmon (Oncorhynchus gorbuscha) in Prince William Sound,Alaska

Our collaborative work focused on understanding the system of mechanisms influencing the mortality of juvenile pink salmon (Oncorhynchus gorbuscha) in Prince William Sound, Alaska. Coordinated field studies, data analysis and numerical modelling projects were used to identify and explain the mechanisms and their roles in juvenile mortality. In particular, project studies addressed the identification of major fish and bird predators consuming juvenile salmon and the evaluation of three hypotheses linking these losses to (i) alternative prey for predators (prey‐switching hypothesis); (ii) salmon foraging behaviour (refuge‐dispersion hypothesis); and (iii) salmon size and growth (size‐refuge hypothesis). Two facultative planktivorous fishes, Pacific herring (Clupea pallasi) and walleye pollock (Theragra chalcogramma), probably consumed the most juvenile pink salmon each year, although other gadids were also important. Our prey‐switching hypothesis was supported by data indicating that herring and pollock switched to alternative nekton prey, including juvenile salmon, when the biomass of large copepods declined below about 0.2 g m^?3. Model simulations were consistent with these findings, but simulations suggested that a June pteropod bloom also sheltered juvenile salmon from predation. Our refuge‐dispersion hypothesis was supported by data indicating a five‐fold increase in predation losses of juvenile salmon when salmon dispersed from nearshore habitats as the biomass of large copepods declined. Our size‐refuge hypothesis was supported by data indicating that size‐ and growth‐dependent vulnerabilities of salmon to predators were a function of predator and prey sizes and the timing of predation events. Our model simulations offered support for the efficacy of representing ecological processes affecting juvenile fishes as systems of coupled evolution equations representing both spatial distribution and physiological status. Simulations wherein model dimensionality was limited through construction of composite trophic groups reproduced the dominant patterns in salmon survival data. In our study, these composite trophic groups were six key zooplankton taxonomic groups, two categories of adult pelagic fishes, and from six to 12 groups for tagged hatchery‐reared juvenile salmon. Model simulations also suggested the importance of salmon density and predator size as important factors modifying the predation process.     

Beneficial effects of thyme (Thymus vulgaris) extract on oxytetracycline‐induced stress response,immunosuppression, oxidative stress and enzymatic changes in rainbow trout (Oncorhynchus mykiss)

The aim of the present study was to investigate the effects of thyme extract (TE) and oxytetracycline (OTC) on rainbow trout (Oncorhynchus mykiss) stress response, immune parameters, oxidative stress and enzymatic changes. The fish were assigned into eight treatments receiving diets with OTC (0 and 2.5 g/kg) and TE (0, 5, 10 and 20 g/kg) for 2 weeks. Thereafter, serum characteristics and gut oxidative status were evaluated. OTC significantly increased serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, and cortisol and glucose levels; however, TE significantly suppressed these changes. OTC significantly decreased, but TE significantly increased gut catalase (CAT) and glutathione peroxidase (GPx) activities. OTC significantly decreased gut superoxide dismutase (SOD) and increased gut glutathione‐s‐transferase (GST) activities, malondialdehyde (MDA) content and blood monocyte percentage; TE significantly mitigated these changes. TE significantly increased serum total protein, total Ig, lysozyme and ACH50, and blood WBC; however, OTC significantly decreased serum lysozyme and ACH50 activities and blood WBC and neutrophil percentage. In conclusion, OTC administration causes immunosuppression, which might be related to deterioration of fish health. TE augments trout innate immune and antioxidant status and is capable to counteract OTC‐induced health and immune deterioration.     

Susceptibility of coho salmon, Oncorhynchus kisutch (Walbaum), to different toxins of Clostridium botulinum

Coho salmon Oncorhynchus kisutch (Walbaum), held at 15°C were tested for their susceptibility to toxins of proteolytic and nonproteolytic Clostridium botulinum types A, B, C₁, C₂, D, E, F, and G administered by the oral and intraperitoneal (i.p.) routes. By the oral route, the fish were most susceptibile to type E neurotoxin, which was lethal at a dose equivalent to 90 mouse intraperitoneal minimum lethal doses (MLDs). The oral lethal dose increased to 2000 MLD for nonproteolytic and proteolytic type F neurotoxins, but the toxin types A, B, and C₁ were not lethal to fish at 2000 MLD and type D was not lethal at 20 000 MLD (highest titre tested). The fish were not susceptible to 200 MLD (the highest titres tested) of type G neurotoxin or C₂ cytotoxin. By the i.p. route, all of the toxins except type G were lethal to coho salmon. Type E neurotoxin was the most toxic at a level of one‐half the mouse MLD. Coho salmon held at temperatures ranging from 1 to 20°C were sensitive to type E neurotoxin by both the oral and i.p. routes. As the temperature decreased the fish became more resistant to type E neurotoxin by the oral route, but the i.p. dose remained one‐half the mouse MLD at all temperatures.     

The effect of competition among three salmonids on dominance and growth during the juvenile life stage

Although non‐native species can sometimes threaten the value of ecosystem services, their presence can contribute to the benefits derived from the environment. In the Great Lakes, non‐native brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) support substantial recreational fisheries. With current efforts underway to restore once‐native Atlantic salmon (Salmo salar) to Lake Ontario, there is some concern that Atlantic salmon will impede non‐native contributions to the recreational fishery because Atlantic salmon exhibit niche overlap with brown trout and rainbow trout, particularly during the juvenile life stage. We therefore examined competition and growth of juvenile Atlantic salmon, brown trout and rainbow trout in semi‐natural streams. We found that brown trout were the most dominant and had the greatest growth rate regardless of what other species were present. Rainbow trout were more dominant than Atlantic salmon and consumed the most food of the three species. However, in the presence of brown trout, rainbow trout fed less frequently and exhibited negative growth as compared to when the rainbow trout were present with only Atlantic salmon. These data suggest that, outside of density‐dependent effects, Atlantic salmon will not impact stream production of brown trout and rainbow trout.     

Piscine reovirus in wild and farmed salmonids in British Columbia,Canada: 1974–2013

Piscine reovirus (PRV) was common among wild and farmed salmonids in British Columbia, western Canada, from 1987 to 2013. Salmonid tissues tested for PRV by real‐time rRT‐PCR included sections from archived paraffin blocks from 1974 to 2008 (n = 363) and fresh‐frozen hearts from 2013 (n = 916). The earliest PRV‐positive sample was from a wild‐source steelhead trout, Oncorhynchus mykiss (Walbaum), from 1977. By histopathology (n = 404), no fish had lesions diagnostic for heart and skeletal muscle inflammation (HSMI). In some groups, lymphohistiocytic endocarditis affected a greater proportion of fish with PRV than fish without PRV, but the range of Ct values among affected fish was within the range of Ct values among unaffected fish. Also, fish with the lowest PRV Ct values (18.4–21.7) lacked endocarditis or any other consistent lesion. From 1987 to 1994, the proportion of PRV positives was not significantly different between farmed Atlantic salmon, Salmo salar L. (44% of 48), and wild‐source salmonids (31% of 45). In 2013, the proportion of PRV positives was not significantly different between wild coho salmon, Oncorhynchus kisutch (Walbaum), sampled from British Columbia (5.0% of 60) or the reference region, Alaska, USA (10% of 58).     

A Toxicokinetic Study of Oxytetracycline Antibiotics in Farmed Pacific White Shrimp,Penaeus vannamei

Toxicokinetics has demonstrated abnormal signs in drug distribution/disposition without waiting until the drug damages the tissues/organs. It is a study of the kinetic assessment of administering high‐dose of oxytetracycline (OTC) to white shrimp. Male Penaeus vannamei in the C–D₀ molting stage, were force fed with medicated feeds at various accurate dose levels including 500, 1000, and 2500 mg/kg‐body weight (BW). After dosing with different time intervals, hemolymph, muscle, and hepatopancreas were collected, and assayed for OTC by validated high‐performance liquid chromatography method. The simulated profile based on the maximum recommended dose was tested to approach the systemic level where the drug was anticipated not to cause significant toxic responses. OTC kinetic profiles in the hemolymph were fitted into the flow limited model having r² value between 0.8341 and 0.9373. The relative affinities for the muscle and hepatopancreas changed at dose level exceeding 1000 mg/kg BW. Although hepatopancreatic clearance was non‐linearly related with dose, the persistence of OTC in muscle after 2500 mg/kg BW dosing was observed to indicate abnormalities in drug distribution/disposition. It was hypothesized that the pharmacokinetic alteration after extreme dosing was because of induction of functional abnormalities in hepatopancreas. In addition, a single administration of OTC at 1000 mg/kg BW was anticipated to be a tolerated dose.     

Can timing of spawning explain the increase in egg size with female size in salmonid fish?

A common observation is that egg size increases with maternal size within populations. Several hypotheses have been proposed to explain this phenomenon. Most recently, it was suggested that the optimal egg size depends on female size due to correlations between (i) breeding time and egg size selection and (ii) female size and breeding time, and as such, the positive egg size–maternal size relationship represents an adaptive strategy. Here, we test the second of these two premises in two salmonid species, Atlantic salmon (Salmo salar) and coho salmon (Oncorhynchus kisutch) for which we have detailed breeding and egg size data. The body size of spawning females decreased throughout the season in coho salmon, but not in Atlantic salmon. Furthermore, we did not find a direct correlation between egg size and breeding time, which would also be expected if this premise was correct. Accordingly, breeding date does not appear to be as important as other factors in shaping among female differences in egg size.     

Chum salmon (Oncorhynchus keta) growth and temperature indices as indicators of the year–class strength of age‐1 walleye pollock (Gadus chalcogrammus) in the eastern Bering Sea

Ecosystem‐based fisheries management requires the development of physical and biological time series that index ocean productivity for stock assessment and recruitment forecasts for commercially important species. As recruitment in marine fish is related to ocean condition, we developed proxies for ocean conditions based on sea surface temperature (SST) and biometric measurements of chum salmon (Oncorhynchus keta) captured in the walleye pollock (Gadus chalcogrammus) fishery in the eastern Bering Sea in three periods (July 16–30, September 1–15 and September 16–30). The main purpose of this paper was to evaluate Pacific salmon (Oncorhynchus spp.) growth as a possible indicator of ocean conditions that, in turn, may affect age‐1 walleye pollock recruitment. Marine growth rates of Pacific salmon are the result of a complex interplay of physical, biological and population‐based factors that fish experience as they range through oceanic habitats. These growth rates can, therefore, be viewed as indicators of recent ocean productivity. Thus, our hypothesis was that estimated intra‐annual growth in body weight of immature and maturing age‐4 male and female chum salmon may be used as a biological indicator of variations in rearing conditions also experienced by age‐0 walleye pollock; consequently, they may be used to predict the recruitment to age‐1 in walleye pollock. Summer SSTs and chum salmon growth at the end of July and September explained the largest amount of variability in walleye pollock recruitment indicating that physical and biological indices of ocean productivity can index fish recruitment.