Marks In Otoliths Research Articles

Genetic characterization of juvenile chum salmon with otolith marks of Japanese salmon hatcheries in the catches of trawl surveys 2016–2021

Chum salmon sample from the catches of autumn trawl surveys in the Sea of Okhotsk (2016–2021), including individuals with otolith marks of Japanese salmon hatcheries (SHs), was analyzed based on microsatellite loci polymorphism. Reference database of eight microsatellite loci frequencies, created before and included 26 samples of chum salmon from major reproductive regions in the Sea of Okhotsk basin, has been updated with data on the microsatellite allele variety of chum salmon from Hokkaido and Honshu. Result s of the research indicate of strong similarity between chum salmon of the Kuril Islands and individuals released from Japanese SHs.

Comparative Analysis of Natural- and Hatchery-Origin Chum Salmon Oncorhynchus keta (Salmonidae) Spawners Identified in Mixed Stock with Otolith Marking

The body length and weight of the hatchery- and natural-origin chum salmon Oncorhynchus keta spawners (identified with the otolith marking technique) in the commercial stock in the Yasnomorka River and the Yasnomorskoe salmon stocking fish hatchery were analyzed in 2015–2019. The proportion of hatchery-origin fish comprised 65.5%, varying from 37.2 to 72.9% from year to year. In addition, 9.2% of specimens had the otolith marks provided by the adjacent salmon stocking fish hatcheries, such as the Sokolniki and Kalinin enterprises. The body weight of the natural- and hatchery-origin chum salmon spawners entered the river for spawning for each age group was not different with a few exceptions. However, the females and males spawn naturally tended to reach the sex maturity at the earlier age, on average, in all their generations for a five-year observation, when compared that to the hatchery-origin fish. Overall, the proportion of fish aged 2+ to 3+ among the hatchery- and natural-origin females comprised 25.1 and 61.5%, respectively. With respect to the hatchery- and natural-origin males, the proportions made up 32.2 and 69.0%, respectively.

Age validation of Black Rockfish, Copper Rockfish, and Cabezon using secondary ion mass spectrometry (SIMS) to elucidate seasonal patterns in otolith stable oxygen isotopes

Stock assessors commonly use models that incorporate biological data such as fish length and age to determine the status of fish stocks and how different management scenarios affect stock size. Ages used in assessment models need to be accurate and precise because ageing error can affect many model inputs and potentially result in stock mismanagement. Despite the requirement for sound age data, few studies have investigated accuracy of ages for groundfish captured in coastal nearshore waters off Oregon, USA. In this study, we validate otolith ages for Black Rockfish (Sebastes melanops), Copper Rockfish (Sebastes caurinus) and Cabezon (Scorpaenichthys marmoratus), three species with recreational and commercial importance to Oregon. Ages obtained by traditional break-and-burn methods were validated using secondary ion mass spectrometry (SIMS) to examine otolith stable oxygen isotope ratios (δ18O) over a fish’s lifetime. This technique relies on the inverse relationship that exists between otolith δ18O and ambient water temperature, and independent counts of δ18O maxima should be comparable to ages obtained by visual counts of otolith growth marks laid down during cold water periods. Locations of δ18O maxima in otolith chronologies matched well with locations of visual growth marks in otoliths of all three species, maxima counts were strongly positively correlated with age, and variation in otolith δ18O decreased with age. However, significant variability in the δ18O chronologies caused by variability in intra-seasonal upwelling and resulting water temperature variations made maxima counts difficult in several samples. Correct interpretation of chronologies required knowledge of location of the first annulus, the compression of growth zones with age, and an assumption of the seasonal amplitude of the ambient water δ18O.

Inter-Otolith Differences in Strontium Markings: A Case Study on the Juvenile Crucian Carp Carassius carassius (Linnaeus, 1758)

The release of hatchery-reared fish fry for restocking is important for the enrichment of fishery resources; however, the effective evaluation of the success rate of marking such fish is challenging. We exposed juvenile crucian carp (Carassius carassius) to a single concentration of SrCl2·6H2O for 5 d and evaluated the efficiency of Sr marking of the fish otoliths (sagittae, asterisci, and lapilli) using an electron probe micro-analyzer. Sr marking signatures formed a peak in all otolith types, with a marking success rate of 100%. The ratio of Sr to Ca in the lapilli and sagittae was higher than that in the asterisci. It took 2 d from the beginning of immersion to the deposition of Sr on the lapilli and sagittae, and the time delay for asterisci was 1 d. For the lapilli and sagittae, it took 16 d to terminate Sr marking and fully recover to the pre-marking Sr level, whereas it was 12 d for the asterisci. The application of the Sr dose had no effect on the survival or growth of the carp. This study demonstrated that the lapilli are the most suitable otolith type for Sr marking observations in crucian carp and provides a theoretical basis and technical support for carp restocking using the Sr marking approach.

Determining salmon provenance with automated otolith reading

We present a computer vision method for identifying and reading hatchery marks in salmon otoliths. Synthetic otolith marks are used at hundreds of hatcheries throughout the Pacific Rim to record the release location of salmon. Each year, human readers examine hundreds of thousands of otolith samples to identify the marks in captured salmon. The data guide hatchery investments and inform dynamic management practices that maximize allowable catch while preserving wild-hatched populations. However, the method is limited by the time required to process otoliths, the inability to distinguish between wild and un-marked hatchery fish, and in some cases classification processes are limited by the subjective decisions of human readers. Automated otolith reading using computer vision has the potential to improve on all three of these limitations. We tested the classification accuracy of transfer learning using previously published deep neural networks pretrained with the ImageNet database and compared it to the classification accuracy achieved using shallow networks developed specifically for otolith reading. The shallow networks achieved better classification accuracy with the available training and test sets. In particular, we report a novel otolith classification algorithm that uses two neural networks trained with an adversarial algorithm to achieve 93% classification accuracy between four hatchery marks and unmarked otoliths. The algorithm relies on hemi-section images of the otolith exclusively: no additional biological data are needed. Our work demonstrates a novel technique with modest training requirements that achieves unprecedented accuracy. The method can be easily adopted in existing otolith labs, scaled to accommodate additional marks, and does not require tracking additional information about the fish that the otolith was retrieved from. Future work should determine the value of expanding the training set and applying the algorithm to a more diverse set of otolith marks.

Genetic evaluation of the unknown contribution of stocked fish in angler catches: a case study using mulloway Argyrosomus japonicus

Stock enhancement involves the augmentation of wild populations with hatchery-reared recruits. Stock enhancement generally also includes a postrelease monitoring program which tracks stocked individuals within the fishery, and this relies on having a means to identify the likely origin of recaptured fish (e. g., physical, otolith, or genetic tags). This study reports the application of sibship analysis to retrospectively infer the origin of mulloway (Argyrosomus japonicus) within stocked estuaries when other means of identification were not available. Eight cohorts of mulloway were stocked into two estuaries across a seven-year period, but only some of the fish released during the program were physically marked with chemical otolith stains. Fish were sampled from stocked estuaries (mostly through an angler-based sampling program) and genotyped for six microsatellite loci, alongside 129 fish sampled from nonstocked estuaries. The presence of multiple sibs within the mixed populations in stocked estuaries was used to infer the origin of captured fish against a background of sibship for known-origin individuals (verified by otolith marks) and sibship levels within unstocked estuaries. The analysis suggested hatchery-reared fish could have contributed 9% of individuals sampled from the augmented populations (7% when corrected for background sibship). The proportion of fish inferred to be of hatchery origin decreased with size (likely due to mortality and migration), and the expected contribution rates for hatchery-reared fish differed among cohorts. The results highlight that sibship analysis may be useful for retrospective genetic evaluation of stocked estuaries.

Does Vaterite Otolith Deformation Affect Post-Release Survival and Predation Susceptibility of Hatchery-Reared Juvenile Atlantic Salmon?

Sagittal otoliths are calcareous structures in the inner ear of fishes involved in hearing and balance. They are usually composed of aragonite; however, aragonite can be replaced by vaterite, a deformity which is more common in hatchery-reared than in wild fish. Vaterite growth may impair hearing and balance and affect important fitness-related behaviours such as predator avoidance. Captive rearing techniques that prevent hearing loss may have the potential to improve fish welfare and the success of restocking programmes. The aim of this study was to test the effect of structural tank enrichment on vaterite development in the otoliths of hatchery-reared juvenile Atlantic salmon Salmo salar, and to assess the effects of vaterite on immediate predation mortality and long-term survival after release into the wild. Fry were reared in a structurally enriched or in a conventional rearing environment and given otolith marks using alizarin during the egg stage to distinguish between the treatment groups. Otoliths were scrutinised for the presence and coverage of vaterite at 6, 13, and 16 weeks after start feeding, and the growth traits were measured for enriched and control fry when housed in tanks. In a subsequent field experiment, juveniles were released in the Rasdalen river (western Norway), and otoliths of enriched reared and control reared fry were scrutinised from samples collected immediately prior to release, from predator (trout Salmo trutta) stomachs 48 h after release and from recaptures from the river 2–3 months after release. Vaterite otoliths occurred as early as 6 weeks after start feeding in hatchery-reared S. salar. Vaterite occurrence and coverage increased with fish length. Enriched rearing had no direct effect on vaterite formation, but enriched reared fry grew slower than control fry. After release into the wild, fewer salmon fry with vaterite otoliths had been eaten by predators, and a higher proportion of fry with vaterite otoliths than those lacking vaterite were recaptured in the river 2–3 months after release. Contrary to expectations, this suggests that vaterite does not increase predation mortality nor reduce survival rates in the wild during the early life stages.

Age validation of age 0-3 wild cod Gadus morhua in the western Baltic Sea through mark-recapture and tetracycline marking of otoliths

The contrasting zones within otoliths are commonly used to infer age of fish, assuming that 1 opaque zone and 1 translucent zone (TZ) form per year. However, the periodicity of zone formation is often un-validated and susceptible to interpretation errors and uncertainties, which propagate into age-structured calculations. The western Baltic cod Gadus morhua (WBC) stock is currently evaluated through an age-based assessment, using the typical, temperate area assumption that TZs form in autumn/winter. The periodicity of zone formation was evaluated through a mark-recapture experiment with juvenile and young adult WBC. During 2014-2017, 9111 wild cod were tagged externally (T-bar anchor tag) and internally (injection with tetracycline-hydrochloride induced a permanent fluorescent mark on their otoliths) and released. Timing of TZ formation was reconstructed through examination of otoliths from recaptured age 0-3 cod for which all required information and otoliths were available (n = 59, length range: 173-500 mm). Contrary to the assumption that TZs are formed during winter, recaptured cod consistently formed 1 TZ per year, between summer and autumn, in both juveniles (age 0-1) and young adults (age 2-3). A calendar year in the otolith is therefore composed of a TZ with opaque material on either side. Coincidence of TZ formation and recent evidence of shallow-water avoidance and reduced feeding and growth in WBC during peak summer suggests that TZs are formed when metabolic demands cannot be met. The results improve accuracy of WBC age estimates and highlight the feasibility and importance of conducting age validation experiments.

Can structural enrichment reduce predation mortality and increase recaptures of hatchery-reared Atlantic salmon Salmo salar L. fry released into the wild?

Captive-reared fish often have poor survival in the wild and may fail to boost threatened populations. Enrichment during the nursery period can in some circumstances generate a broader behavioural repertoire than conventional hatchery production. Yet, we do not know if enrichment promotes survival after release into the wild. We conducted a field experiment during three field seasons using age 0+ year Atlantic salmon Salmo salar to investigate if enrichment during rearing, in the form of structural complexity (shelters), reduced immediate (within 2 days after release) predation mortality by piscine predators (brown trout Salmo trutta) and if such rearing environments improved long-term (2-3 months after release) post-release survival. In addition, we investigated if predation mortality of released fry was size-selective. S. salar fry were reared in a structurally enriched environment or in a conventional rearing environment and given otolith marks using alizarin during the egg stage to distinguish between enriched and conventionally-reared fry. The outcome from the field experiments showed that structural enrichment did not consistently reduce immediate predation mortality and it did not improve, or had a negative effect on, the recapture rate of fry from the river 2-3 months after release. The data also showed that enriched rearing tended to reduce growth. Additionally, we found that S. trutta predators fed on small individuals of the released fry. Overall, the data suggest that structural enrichment alone is not sufficient to improve long-term survival of hatchery-reared fish after release and that other factors might affect post-release survival.

北海道南西部の遊楽部川における産卵後斃死サケの耳石温度標識から推定した自然産卵サケの起源

放流種苗に耳石温度標識魚と無標識魚が混在し，遡上期の捕獲施設が中流域にある北海道南西部のサケ増殖河川，遊楽部川において，2015年度の遡上時期に上流域および下流域で自然産卵後斃死した親魚（ホッチャレ）の耳石温度標識の割合からふ化場魚と野生魚を推定した。その結果，上流域では，期間を通じて自然産卵個体のほとんどがふ化場魚であると推定された。下流域では，標識魚は期間を通じて放流時の標識率を下回り，自然産卵由来の野生魚とふ化場魚が自然産卵していることが示された。

Can calcein and alizarin complexone be used for double immersion marking of juvenile qingbo Spinibarbus sinensis?

Calcein (CAL) from 50 to 250 mg/l and alizarin complexone (ALC) from 100 to 300 mg/l were used for double immersion marking of juvenile qingbo Spinibarbus sinensis. With the exception of the scales, double immersion for 24 h produced detectable double marks in otoliths (sagittas and asterisci), barbs, fin rays (dorsal, pectoral, ventral, anal, and caudal), and fin spines (dorsal, pectoral, ventral, and anal) after 90 days in a laboratory growth experiment. Green fluorescent rings produced by CAL were considerably closer to the inside of the bony structures (including otoliths, barbs, fin rays, and fin spines) than red fluorescent rings produced by ALC. Sagittas, asterisci, and barbs showed acceptable fluorescent marks at higher concentrations (250 mg/l CAL and ≥ 200 mg/l ALC, ≥ 200 mg/l CAL and 300 mg/l ALC, 150–250 mg/l CAL and 250–300 mg/l ALC, respectively). Fin rays and fin spines treated by 200 mg/l CAL and 250 mg/l ALC and 250 mg/l CAL and 300 mg/l ALC simultaneously had both acceptable CAL and ALC marks. There was no statistically significant difference on the survival or growth of marked fish compared to the controls throughout the experiment (p > 0.05). The results suggest that double immersion with CAL and ALC is suitable for double mass-marking of juvenile S. sinensis, and these double marks are useful in the experimental development of biological research or restocking methodologies.

Tetracycline marks visible in Baltic cod Gadus morhua otoliths stored for 40 years.

Baltic cod Gadus morhua otoliths marked with oxytetracycline (OTC) in 1974-1975 had been sectioned and the sections stored in paper envelopes at room temperature in dry, dark conditions. After 40 years of storage, the historic OTC marks were still clearly visible showing that OTC is suitable for long-term chemical marking of otoliths. They were, however, noticeably paler than marks in recently recaptured and archived Baltic G. morhua otoliths, chemically tagged with tetracycline at similar dosage to the historic otoliths.

Otolith fluorescent and thermal marking of elongate loach (Leptobotia elongata) at early life stages

The elongate loach (Leptobotia elongata) is an important fish species for artificial release program during the development of hydropower stations in upper Yangtze River drainage. We explored the chemical and thermal marking of otoliths for the species in this study, hoping to provide appropriate marking approaches for it. Chemical marking was conducted by immersing elongate loach in alizarin complexone (ALC) of concentrations 50–250 mg L−1 or alizarin red S (ARS) of concentrations 30–150 mg L−1. The results demonstrated that all concentrations of ALC and ARS treatments had 100 % fluorescent marks in sagittae and lapilli (grade ≥ 3), and that mark quality and mortality increased with increasing of fluorochrome concentration, while decreased with increasing of total length. The optimal conditions of otolith fluorescent marking for larval and juvenile elongate loach were to immerse in 50–100 mg L−1 ALC or 30–90 mg L−1 ARS solutions for 12–24 h. Larvae thermally marked by being exposed to five water temperature regimes represented different patterns of otolith increment. The control of duration in the heated water could produce some narrow or wide increments, and there was a significantly positive relationship between increment width and duration in heated water in each cycle of water temperature fluctuation. More and complicated otolith mark patterns could be produced by combining thermal marking with fluorescent immersion. Considering efficiency, operability and low-cost, the ARS immersing and thermal marking methods are recommended for mass-marking elongate loach at early life stages.

The Effect of Water Hardness on Mortality of Zebrafish (Danio rerio) During Exposure to Oxytetracycline.

Marking of fish otoliths with oxytetracycline and tetracycline is a widely used method to evaluate the effectiveness of stocking operations. Available protocols for the labeling of fish specify a number of factors influencing mark quality and potential risk for fish during marking. This study investigates the influence of water hardness on mortality of freshwater fish during marking with OTC. In order to pursue this question complexation of OTC with Mg(2+) and Ca(2+) cations was measured spectrophotometrically. Furthermore, zebrafish (Danio rerio) were immersed in OTC solutions (1200 mg/L; 48 h immersion) combined with varying levels of water hardness (5.5, 15.5, 25.5, 32.5°dH). The amount of OTC-Mg-Ca-complexes was positively correlated to water hardness. Moreover, it could be demonstrated that mortality of zebrafish during marking varied as a factor of water hardness. Highest mortalities occurred at the lowest (5.5°dH) and the highest (32.5°dH) tested levels during marking with OTC.

Natural growth, otolith shape and diet analyses of Odontesthes nigricans Richardson (Atherinopsidae) from southern Patagonia

Age and growth, otolith shape and diet of Odontesthes nigricans were analysed in order to provide an insight into the life history of the species and furthermore, to assess their possible use as a tool for discriminating silverside populations from the South Atlantic Ocean (Punta María) and Beagle Channel waters (Varela Bay). The age and growth analysis was performed by counting daily increments and annual marks in sagittae otoliths. Length-at-age data of individuals <65 mm standard length (SL) were fitted to the Laird–Gompertz model (SLt = 6.22 exp 2.45 [1−exp (−0.02t)]), which provided an excellent description of the pattern of daily growth for O. nigricans juveniles from Varela Bay. The spawning period was also assessed through back-calculation of hatching dates and it extended from November to February. The count of annual marks in larger individuals identified 7 year classes (0+ to 6+) in Varela Bay and 6 year classes (0+ to 5+) in Punta María. The von Bertalanffy growth model explained more than 95% of the growth patterns observed in O. nigricans from Varela Bay (SLt = 245.49 [1 − exp −0.24(t+0.46)]) and Punta María (SLt = 345.09 [1 − exp −0.15(t+0.31)]). Particularly, k and SL∞ varied significantly between sampling sites; reaching Punta María a larger SL∞ value with a lower k. Otolith shape variation was also explored using elliptical Fourier analysis and it showed significant differences between Varela Bay and Punta María populations. Furthermore, gut content analysis characterized O. nigricans as an invertebrate predator, being benthic organisms the most important components of its diet, which also showed significant site dependence. The use of all these analyses contributed to a holistic approach which maximized the likelihood of correctly identifying both O. nigricans populations in the southernmost limit of the species distribution.

Mass marking of stocked European glass eels (Anguilla anguilla) with alizarin red S

AbstractThis study describes a mass marking method suitable for European glass eel Anguilla anguilla, avoiding osmotic shock and reducing fish stress. During a single day, 360,000 glass eels intended for a stocking operation were bathed into an alizarin red S (ARS) solution, at a density of 346 ind.·l−1 before being released into a freshwater marsh along with unmarked glass eels. After 15 days, examination of marked and unmarked eels kept in enclosures in the marsh showed 100% of otoliths had been successfully marked and that no excess deaths related to marking process had occurred. Seven months after stocking, results from biometric measurements and otolith analysis, carried out on a sample of 53 elvers caught by electrofishing and belonging to the size class of the 0+ cohort, suggest that: (i) the proportions of marked and unmarked remained unchanged, hence suggesting that the marking process had not caused excess mortality, (ii) there was no difference in length, body mass or condition factor between marked and unmarked individuals, demonstrating that marking had caused no harmful effect after 7 months, and (iii) ARS marks in otoliths remained clearly visible. The benefits of this ARS mass marking technique are discussed through a stocking operation.

Osmotic induction improves batch marking of larval fish otoliths with enriched stable isotopes

Abstract Otolith marking with enriched stable isotopes via immersion is a recent method of batch marking larval fish for a range of research and industrial applications. However, current immersion times and isotope concentrations required to successfully mark an otolith limit the utility of this technique. Osmotic induction improves incorporation and reduces immersion time for some chemical markers, but its effects on isotope incorporation into otoliths are unknown. Here, we tested the effects of osmotic induction over a range of different isotope concentrations and immersion times on relative mark success and strength for 26Mg:24Mg, 86Sr:88Sr and 137Ba:138Ba on Atlantic salmon (Salmo salar) larvae. 71% and 100% mark success were achieved after 1 h of immersion for 86Sr (75 µg L−1) and 137Ba (30 µg L−1) isotopes, respectively. Compared with conventional immersion, osmotic induction improved overall mark strength for 86Sr and 137Ba isotopes by 26–116%, although this effect was only observed after 12 h of immersion and predominately for 86Sr. The results demonstrate that osmotic induction reduces immersion times and the concentrations of isotope required to achieve successful marks. Osmotically induced isotope labels via larval immersion may prove a rapid and cost-effective way of batch marking fish larvae across a range of potential applications.

Stable isotope marking of otoliths during vaccination: a novel method for mass-marking fish

Tagging or marking of fishes enables the collection of population-based information for ecological research, yet few techniques enable 100% mark detection success. We tested a new mass-marking technique: otolith marking with enriched stable isotopes delivered during vaccina- tion. Atlantic salmon (Salmo salar) parr were injected in either the abdominal cavity or muscle with a combination of enriched 137 Ba, 86 Sr and 26 Mg, using 1 of 3 carrier solutions (water, vaccine, vaccine mimic). Laser ablation inductively coupled plasma mass spectrometry of the otoliths indi- cated that 137 Ba and 86 Sr isotope enrichment treatments achieved 100% mark success, with 0 to 34% success for 26 Mg, compared to experimental controls. Mark strength was greater when enriched isotopes were injected into the abdominal cavity compared to muscle. Isotope markers did not affect fish condition or survival. Marks could be differentiated with 100% success from the background levels present in wild parr collected from 22 Norwegian rivers. Stable isotope mark- ing via vaccination with enriched stable isotopes is a mass-marking technique that, once opti- mised, could allow for cost-effective differentiation of wild and escaped farmed fish for each inde- pendent farming area.

Detection of transgenerational barium dual-isotope marks in salmon otoliths by means of LA-ICP-MS

The present study evaluates the use of an individual-specific transgenerational barium dual-isotope procedure and its application to salmon specimens from the Sella River (Asturias, Spain). For such a purpose, the use of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in combination with multiple linear regression for the determination of the isotopic mark in the otoliths of the specimens is presented. In this sense, a solution in which two barium-enriched isotopes ((137)Ba and (135)Ba) were mixed at a molar ratio of ca. 1:3 (N Ba137/N Ba135) was administered to eight returning females caught during the spawning period. After injection, these females, as well as their offspring, were reared in a governmental hatchery located in the council of Cangas de Onís (Asturias, Spain). For comparison purposes, as well as for a time-monitoring control, egg and larva data obtained by solution analysis ICP-MS are also given. Otoliths (9-month-old juveniles) of marked offspring were analysed by LA-ICP-MS demonstrating a 100% marking efficacy of this methodology. The capabilities of the molar fraction approach for 2D imaging of fish otoliths are also addressed.

Growth and age of Atlantic saury, Scomberesox saurus saurus (Walbaum), in the northeastern Atlantic Ocean

The Atlantic saury Scomberesox saurus saurus (Walbaum) is a widely distributed epipelagic nekton species in the north Atlantic. It is considered one of the most abundant small pelagic species in the north Atlantic and is of increasing interest to commercial fisheries in American and European countries.Ageing of Atlantic saury is difficult, annual marks in otoliths, scales and other structures are often not present or are difficult to interpret, resulting in non-robust estimations.Growth of the Atlantic saury, from the northeastern Atlantic Ocean was studied by examining otoliths and scales for the presence of putative annual and daily growth marks. A description of Atlantic saury saggital otolith microstructure is given. No annual structures were observed on scales or otoliths. Counts of otolith micro-increments suggest that Atlantic saury exhibit a much faster growth rate than previously reported. Micro-increment counts ranged from 113 to 258 in fish from 110mm to 288mm of body size, suggesting that Atlantic saury is a short lived species. Assuming that otolith growth increments are deposited at a rate of one per day, average growth rates from hatching up to eight months old exceeded 1mm/day. The saury population available for exploitation in the northeast Atlantic is dominated by fish that are most likely less than one year old. Management of short-lived, forage species require special considerations and represents a challenge to fishery science.