Galaxias Argenteus Research Articles

Evaluating intra- and inter-life stage density-dependent dynamics for management of perennial amphidromous fish.

Compensatory density-dependent (DD) processes play an integral role in fisheries management by underpinning fundamental population demographics. However, DD processes are often assessed only for specific life stages, likely resulting in misleading evaluations of population limitations. Here, we assessed the relative roles of intra- and inter-life stage DD interactions in shaping the population dynamics of perennial freshwater fish with demographically open populations. Specifically, we monitored populations of amphidromous banded kōkopu (Galaxias fasciatus), giant kōkopu (Galaxias argenteus), and shortjaw kōkopu (Galaxias postvectis) in five streams where migratory post-larvae are fished and in three no-take ("closed") streams located on New Zealand's South Island for two years. Using mark-recapture data, we investigated whether fishing altered densities of "small" (non-territorial recruits ≤1-year-old) and "large" (territorial fish >1-year-old) kōkopu size classes, and how subsequent density shifts affected the apparent survival and growth of each class while controlling for other confounding factors (e.g., habitat characteristics). We found that closed areas had substantially greater biomass of small kōkopu, particularly following the two-month fishing season. Despite this greater influx of recruits, there was no difference in the biomass of large kōkopu at the species level, or as a combined assemblage between stream types. This indicated that although fishing of post-larvae reduced recruit influxes into adult habitats, there was no subsequent evidence of recruitment-limitation within adult populations. Instead, kōkopu demographics were underpinned by intra- and inter-life stage DD competition and predation. Greater large fish densities played a key role in regulating the survival, growth, and/or presence of various kōkopu classes. In contrast, greater small fish densities had positive effects on the growth of opportunistic and insectivorous congeners, likely due to cannibalism and altered foraging behaviors, respectively. Our study details the prominent role of intra- and inter-life stage DD interactions in regulating the population dynamics of perennial migratory freshwater fishes, even in populations with inhibited recruit and juvenile availability. We emphasize the importance for fisheries management to implement recruitment dependencies and complex interactions between distinct life stages to avoid deleterious DD responses and ensure population persistence.

Tracing transgenerational plasticity through ova fatty acid biomarkers in Giant Kōkopu (Galaxias argenteus)

ABSTRACT Broodstock management has traditionally focused on heritable traits and diet-induced gamete quality. However, the potential of transgenerational plasticity (TP) underscores the importance of understanding adaptive trait transfer in aquaculture, where the sustainability of production can be hampered by mortality arising from disease and stress. Notably, the role of fatty acids (FAs) as important biomarkers is an untapped area of TP research with implications for the management of new aquaculture species. We assessed TP in Giant Kōkopu (Galaxias argenteus) by comparing the ova FA profiles of broodstock across five captive generations; wild-caught, F1, and three successive F2s. Our study revealed intergenerational shifts in ova FA profiles. We encountered a significant decline in C18:1 (n-9) (Oleic Acid, OLA) and C20:4 (n-6) (Arachidonic acid, ARA), and an increase in C16:0 (Palmitic acid, PAL) from wild-caught to captive-bred broodstock. These shifts reveal that latter generations of captive-bred G. argenteus are reducing the provision of FAs associated with stress (OLA) and lower reproductive success (ARA), while increasing those linked to improved immune response (PAL), signalling a significant adaptation to captivity. Our findings help elucidate the theoretical understanding of TP through the use of FAs as biomarkers, providing practical insight for broodstock management.

Opportunistic discovery of giant kōkopu (Galaxias argenteus) spawning in a tidal reach: site description and implications

ABSTRACT This paper reports the first observation of a giant kōkopu (Galaxias argenteus) spawning site in a tidal waterway and illustrates the usefulness of DNA barcoding for opportunistic discoveries that in this case involved the collection of a single egg. We describe key characteristics of the spawning site and compare them with the only other recorded giant kōkopu spawning location which was found in a much different environmental context far inland. This is also a novel observation of giant kōkopu and īnanga (G. maculatus) spawning on the same section of riverbank. Eggs from the two species occupied the same vertical elevation band, which together the consideration of tidal heights and the egg development stage suggest that the spawning event was triggered by a tidal cue. We discuss the implications of more widespread giant kōkopu spawning in tidal waterways, including historical perspectives contributing to their decline and the potential to reverse these trends.

Optimization of Artemia Feed Regimes for Larval Giant Kōkopu (Galaxias argenteus)

Optimizing the initial live feed is critical to success in fish larviculture in terms of both larval health and productivity. It is also vitally important due to the significant cost of provisioning live feeds. Glaxiids are high-value diadromous fish species found in parts of the Southern Hemisphere, which are wild-harvested and sold for human consumption in their larval form. In the emerging aquaculture of galaxiids, the live feed makes up a great proportion of the production cycle and is therefore a significant factor in achieving the economic viability of their production. In New Zealand, the endemic galaxiid species giant kōkopu (Galaxias argenteus) is considered suitable for aquaculture; however, little is known of their larval-feeding requirements. This study compares the growth performance and survival of giant kōkopu larvae over a four-week period when fed different proportions of first-molt Artemia nauplii (instar-I) and enriched, second-molt-onward Artemia (instar-II+) for different durations. The larvae in the treatment group which received the greatest proportion of Instar-I Artemia for the longest duration had the lowest mean wet weight and survival, leading to the production of the lowest total biomass of fish larvae when compared to the other feed treatments. The feed treatment that received only instar-II+ Artemia achieved an equally best total productivity. While the treatment fed a partial initial duration of mixed instar-I and instar-II+ Artemia achieved the same total productivity, the individual larvae were heavier and their body length was longer. The latter feed treatment appears to offer the best balance between the availability of feed particles in the optimum size range and a higher level of digestibility given that instar-I Artemia had higher levels of highly unsaturated fatty acids and polyunsaturated fatty acids.

Comparison of Three Artificial Diets for the Larviculture of Giant Kōkopu (Galaxias argenteus)

The selection of artificial feed is critical to the success of larviculture of fin fish and requires knowledge of the varied species-specific dietary and nutritional requirements. With the emergence of commercial aquaculture of giant kōkopu, Galaxias argenteus, there is a need to understand the species-specific needs for artificial feeds in larviculture. Consequently, this study compares three commercial artificial dry feeds; Otohime, Artemac and O.range on the growth of recently weaned giant kōkopu. Larvae fed with Otohime outperformed both Artemac and O.range treatments by achieving the highest wet weight after 67 days, greater by at least 47% on average than both Artemac and O.range. These differences in larval performance are likely to be due to the higher protein:energy ratio and EPA content of Otohime. High DHA and ARA in the diets in absolute terms or in relation to EPA did not result in added benefit for growth performance. This study provides an important first step in identifying the nutritional needs of larval giant kōkopu which can assist in improving their commercial aquaculture production.

Improving the weaning of larval giant kōkopu, Galaxias argenteus: An emerging aquaculture species

AbstractUsing live feed in fish larviculture is more expensive and challenging than formulated feeds, incentivizing the early weaning of larvae. In New Zealand, the aquaculture of larval giant kōkopu, Galaxias argenteus, is being commercialized because of its high value and to supplement the wild fishery. As an emerging aquaculture species, inefficiencies remain in the production process, inhibiting financial viability. This study reports on the ability of these larvae to consume formulated larval diets across four ages (18, 21, 25, and 28 days after hatching, DAH) at each of the three daily feeding events (Morning, Midday, and Afternoon) during commercial production. At 18 DAH, little to no formulated feed was consumed at either of the three feeding events throughout the day. At 21 DAH, mean gut fullness increased and the number of fish with empty stomachs reduced by the end of the Morning and Afternoon feeding events. Both variables improved further for larvae at 25 and 28 DAH. Formulated feed consumption did not differ between larvae aged 25 and 28 DAH indicating that 3 days of feeding live feed could be removed from the feed regime. This change would save 13% on the cost of live feed; however, further research is required to determine the potential impacts on growth and survival.

First observations and early life-history aspects of lake rearing galaxiid larvae in the lower Waikato River Basin, New Zealand

ABSTRACT Larval behaviour for many of New Zealand’s diadromous freshwater fish is inadequately described. Diadromy for many amphidromous species is not obligatory however, and where conditions are suitable, freshwater larval rearing may be facilitated. Where this occurs in lakes, opportunities to document the composition and conditions supporting larval rearing exist. Boat trawling was undertaken across nine lowland lakes in the Lower Waikato over four consecutive winters with a focus on larval galaxiids. Galaxiid larvae were captured in surface water habitats in all but one lake, with banded kōkopu (Galaxias fasciatus) and giant kōkopu (Galaxias argenteus) the most common species detected. One lake, Lake Waahi, consistently resulted in the most galaxiid captures for effort expended. Analyses of larvae from this and other lakes indicated that two sizes predominated in catches and that larger, older larvae were predominantly G. fasciatus while smaller, younger larvae were predominantly G. argenteus. Stomach contents indicated that two non-native zooplankton species predominated in the diet of larvae, the Holarctic daphnia, Daphnia galeata, and the Australian calanoid copepod Boeckella symmetrica. This study provides new information regarding the timing, movement and predicted recruitment of native fish species in this river basin that has important implications for lake and river management.

Haematological and metabolic profiles of brooder giant kokopu, Galaxias argenteus (Gmelin 1789) based on sex and temperature

This study assessed the selected peripheral blood haematological parameters and metabolite profiles linked to liver, serum and muscle samples in 3-year-old male (weight = 131.19 ± 29.24 g; total length = 21.33 ± 1.20 cm; n = 5) and female (122.96 ± 27.04 g; total length = 21.09 ± 1.09 cm; n = 5) giant kokopu (Galaxias argenteus) broodstock cultured at 12°C and 16°C. Temperature and sex did not influence haematocrit values or counts of total blood cells, erythrocytes and leucocytes. However, fish reared at 16°C had higher thrombocyte counts, whereas those kept at 12°C exhibited the highest proportion of lymphocytes. At the metabolic level, sex was the main factor that influenced metabolite levels across tissues, with particularly higher amino acid metabolites in liver of females. Changes linked to the interaction between temperature and sex showed significant differences in fatty acid profiles of liver, and in amino acids in muscle and serum samples. Males kept at 16°C exhibited decreased levels of myristic acid and nonadecanoic acid linked to homeoviscous adaptation. In females, levels for energy metabolites including tyrosine and aspartic acid (in muscle), and alanine (in serum) were disturbed at 16°C. The study provides insights into preliminary haematological and metabolic effects associated with sex and temperature in galaxiids.

Freshwater reserves for fisheries conservation and enhancement of a widespread migratory fish

AbstractAs management tools, freshwater reserves are under‐represented in protected area networks for fisheries conservation and enhancement. This is surprising considering that freshwater ecosystems, and the biodiversity they support, are among the most threatened worldwide.We compared freshwater reserve types established to prevent overexploitation of migratory galaxiids (mostly īnangaGalaxias maculatus) from fishing and evaluated their performance as reproductive reservoirs. We studied 10 streams classified into three a priori types: (a) closed, (b) partially closed and (c) open streams.Closed streams had greater abundances, biomasses and egg production ofG. maculatusdespite having a greater proportion of smaller fish compared to partially closed and open streams. Community‐level analyses indicated differences in fish assemblages between closure types. Large, native, predatory fish (longfin eelAnguilla dieffenbachii, shortfin eelAnguilla australisand giant kōkopuGalaxias argenteus) were more common in closed streams.Overall, there were notable reserve effects related to closed streams. There was slight evidence that partially closed streams conferred some fisheries benefits compared to streams open to fishing. While the limited number of reserve streams warrants some caution in conclusions, partial closures may still be worthwhile as a management tool where complete closure to fishing is not feasible.Closures can be effective in increasing fish numbers, albeit at a cost of smaller sized individuals, most likely because of density‐dependent processes relating to food and habitat. Despite clear benefits in total egg production of populations in closed streams, it remains unclear how these benefits may translate across the full life history of the annualG. maculatus.Synthesis and applications. We demonstrate that freshwater reserves have many of the ‘reserve effects’ observed in more common marine reserves, but there are also important differences. Stream closure should be considered as one potential management tool that is unlikely to be effective unless stream habitats are returned to more pristine states. Our effort to evaluate the explicit effects of different reserve types across different spatial scales is the first we know of for migratory freshwater fishes, providing useful insights for adjusting the current reserve network and establishing new reserves.

Morphometric and energetic development of artificially reared giant kōkopu (Galaxias argenteus)

The larvae of some freshwater fish species of the Galaxiidae family are highly-prized in local cuisines in parts of the Southern Hemisphere, however, supplies from wild fisheries are limited. In New Zealand, the larval form of giant kōkopu, Galaxias argenteus, has long been held as a potentially viable aquaculture species due to its high market price (US$70–115 kg−1) and the limited supply of ‘whitebait’ from the wild fishery. However, little is known about the larval stages of this species and the current culture techniques result in poor growth performance and high mortality. This study describes aspects of the morphological development, and larval feeding requirements of giant kōkopu to assist in advancing their aquaculture. Morphometric characteristics of larval giant kōkopu that are critical to the success of larviculture were measured over the 77 day production period, from hatch to harvest. The initial slow growth of the larvae appears to be a result of rapid depletion of endogenous energy reserves prior to initiation of first feeding, while the extent of eye pigmentation and the presence of an open mouth upon hatching indicate that initiating feed provision should be brought forward from 3 DAH. Mouth gape width at hatch was 348 μm and increased rapidly in the first four weeks to 651 μm suggesting that larger live feed items could be used as the initial feed, such as instar-II Artemia. At harvest, the larvae varied enormously in size and condition, with larger fish showing early signs of metamorphosis, such as increasing opacity of flesh and coloration of internal organs. The extent of this variability reduces productivity, increases waste and results in a lower quality product. The results confirm that an improved understanding of the developmental biology of the larvae can assist in providing a more effective feeding regime, particularly for determining the timing of first feed provision and the feed particle size requirements throughout larval development. Consequently, heterogenous growth performance is an aspect of production that needs further attention for developing the efficient aquaculture production of this species.

Effect of anticoagulants on farmed giant kokopu, Galaxias argenteus (Gmelin 1789) haematological parameters and erythrocyte fragility.

We sought to determine a compatible anticoagulant for routine haematological and physiological assessments with giant kokopu (Galaxias argenteus), an endemic New Zealand fish. We observed that blood treated with lithium heparin (LH) rapidly coagulated and haemolysed, making it unsuitable for G. argenteus. Dipotassium ethylenediaminetetraacetic acid (K2 EDTA) and trisodium citrate (citrate) effectively prevented blood coagulation. K2 EDTA-treated erythrocytes exhibited the least mean haemolysis and mean corpuscular fragility. Further studies into prolonged storage effects of citrate and K2 EDTA are recommended to find a compatible anticoagulant for use with G. argenteus blood.

Haematological and metabolic profiles associated with age and sex in giant kokopu (Galaxias argenteus) (Gmelin 1789) broodstock

This study characterized selected peripheral blood (PB) haematological parameters, liver, serum and muscle metabolic features in 3- and 5-year-old male and female giant kokopu (Galaxias argenteus) broodstock reared indoor at 16°C. Sex and age did not affect PB total cell count and haematocrit values. Nonetheless, higher erythrocytes in 5-year-old fish, elevated thrombocyte and lymphocyte counts in 3-year-old fish indicate age-specific cellular regulation. Higher thrombocyte counts in female fish suggest sex-specific regulation. At a metabolic level, liver abundance for long chain saturated fatty acids (FAs) was higher in males, whereas females had elevated levels of polyunsaturated FAs. Essential and non-essential amino acids (AAs) in liver and serum were also elevated in females compared to males. These findings suggest differential allocation of FAs and AAs to reflect requirements for gonadal, development and provisioning. Similarly, age significantly resulted in higher liver and serum abundances of some non-essential AAs in 3-year-olds compared to 5-year-old fish, suggesting higher metabolism in younger fish. Overall, results enhance our understanding of sex- and age-based differences in fish haematology, muscle, liver, and serum metabolite profiles in healthy G. argenteus. Future studies should carefully consider potential age- and sex-specific differences in metabolic responses.

The effects of broodstock generation on ova fatty acid profile in Giant Kokopu Galaxias argenteus

ABSTRACT The ability of different broodstock generations to provision lipids to their gametes is often overlooked in aquacultured freshwater fish. In this study we investigated the ability of two generations (F1 & F2) of Giant Kokopu (Galaxias argenteus) to provision fatty acids into their eggs. Here we show that eggs of captive-bred females (F2) displayed different relative fatty acid concentrations compared with eggs of females bred from wild fish (F1). F2 generation eggs showed significantly lower total mono unsaturated fatty acids (MUFA) concentration, predominantly through lower C18:1(n−9) Oleic acid, and higher total poly unsaturated fatty acids (PUFA) concentration, predominantly through higher 22:6(n−3) docosahexaenoic acid [DHA]. Furthermore, Oleic to n−3 fatty acid ratio, and Oleic to DHA ratio, both declined significantly from F1 to F2 generation. Our results suggest an elevated capacity of F2 females to provision better ratios of essential fatty acids during reproduction, most likely due to a transgenerational adaptive response, either to the fed diet or to a predictable laboratory environment. The findings of this study have important implications for aquaculture management in new captive freshwater species, particularly in aiding identification of more adapted broodstock generations.

To sea or not to sea? Multiple lines of evidence reveal the contribution of non‐diadromous recruitment for supporting endemic fish populations within New Zealand's longest river

Abstract Otolith microchemistry was used to identify marine‐ versus freshwater‐derived recruitment of three native freshwater fish species belonging to the southern hemisphere family Galaxiidae, in New Zealand's longest river system, the Waikato River. Water chemistry data for trace elements and 87Sr/86Sr isotope ratios were collected from five lentic and 10 lotic water bodies throughout the lower river floodplain. Potential spawning sites for galaxiids were compared with values obtained by laser ablation inductively coupled mass spectrometry (LA‐ICPMS) depth profiling of young‐of‐the‐year otoliths sampled from fish in nine lower river catchment sites. Otolith chemical signatures from the larval rearing period indicated that catchment‐scale recruitment for two species, Galaxias argenteus (Gmelin, 1789) and Galaxias fasciatus Gray, 1842, was driven predominantly by non‐diadromous recruitment from one lake (Lake Waahi). In contrast, diadromous recruitment appeared to be more common for Galaxias maculatus (Jenyns, 1842); however, non‐diadromous specimens were also identified for the first time from a New Zealand river. Reversing lake outlet flows linked to river stage appears be important in facilitating the dispersal of rheotactic larvae out of lakes, suggesting that lake outflow management at key times could be used to sustain this ecologically important function. This study highlights that some water bodies can supply a disproportionately large number of recruits to support fish populations within the wider riverscape. Identifying these water bodies and managing them to sustain recruitment is key to the conservation of non‐diadromous Galaxiidae in this modified lowland environment

Assessing sperm membrane viability using flow cytometry in farmed New Zealand giant kokopu Galaxias argenteus

ABSTRACTWe employed flow cytometry to assess plasma membrane viability of sperm cells in farmed giant kokopu Galaxias argenteus, an endemic amphidromous New Zealand fish. Specifically, the variables of fish size (TL mm) and weight (grams) were assessed against sperm viability. We found no significant difference (P < .05) in sperm viability when compared across size and weight distribution of G. argenteus. This study shows that flow cytometry is an effective, accurate and rapid method for analysing sperm viability in G. argenteus.

Efficacy of 12‐mm Half‐Duplex Passive Integrated Transponder Tags in Monitoring Fish Movements through Stationary Antenna Systems

AbstractGlobally, many freshwater fishes are declining in distribution and abundance, but for many species conservation measures are hindered by a limited knowledge of their ecology. Recent development of 12‐mm half‐duplex (HDX) passive integrated transponder (PIT) tags has broadened the potential application of this technology for studying habitat selection and migration of freshwater fishes. However, the limited read range of the smaller 12‐mm PIT tags can limit their functionality in ecological studies. The present study used four migratory fish species to test the efficacy of different PIT antenna designs for detecting 12‐mm HDX tags in small‐ and medium‐sized rivers. Three types of pass‐through antennae were created and coupled to either a single reader or multiplexor board. Across single‐reader and multiplexor systems, the detection efficiencies for Giant Kokopu Galaxias argenteus, Shortfin Eel Anguilla australis, and New Zealand Longfin Eel Anguilla dieffenbachii ranged between 87% and 97%. Adult Pouched Lamprey Geotria australis also had a high detection rate of 74%, even though several other migration routes existed that were unmonitored. Overall, the present study shows that with appropriate antenna design, the 12‐mm HDX PIT tag can be effective for monitoring a variety of fish species. Although the antennae in the present study had a maximum width of 6.1 m, the spaced double‐coil antenna design may increase efficacy of the 12‐mm tag in larger rivers.Received April 27, 2017; accepted September 1, 2017 Published online October 30, 2017

First observations on the timing and location of giant kōkopu (Galaxias argenteus) spawning

The giant kōkopu, Galaxias argenteus (Gmelin, 1789), is the largest of the galaxiid species and is endemic to New Zealand. While it was the first of the galaxiid species to be described, knowledge of its ecology remains relatively poor, particularly with respect to the reproductive phase of its life-cycle. This article describes the first observations of giant kōkopu spawning sites in the natural environment. A total of nine spawning sites have been discovered across two spawning seasons in an urban stream in Hamilton, New Zealand. Giant kōkopu are confirmed to follow a similar spawning strategy to the other whitebait species. Eggs are deposited in riparian habitats while temporarily submerged by elevated water levels. Eggs then develop terrestrially before hatching when the egg deposition sites are re-inundated during later high flows. This spawning strategy leaves giant kōkopu highly susceptible to flow regime and riparian alterations.

Effects of salinity and temperature on artificial cultivation and early ontogeny of giant kokopu, Galaxias argenteus (Gmelin 1789)

Attempts at artificial propagation and rearing of juvenile galaxiids (‘whitebait’) have been hindered by low fecundities and survival. To circumvent these issues, we subjected wild and captivity-acclimated giant kokopu (Galaxias argenteus), a hitherto unexplored galaxiid, to captive breeding protocols and evaluated the effects of salinity and temperature on egg fertilisation, incubation duration and hatching. Eggs sourced over several spawning seasons were subjected to different salinity (0, 9, 15, 20 and 30–35 PSU) and temperature (4, 10, 15 and 17°C) combinations. Average fertilisation rates were highest (95%) when gametes were activated in fresh water (0 PSU) and declined as salinity increased. Average hatch rates were highest (71–68%) when eggs were incubated in fresh water (0 PSU) at 10°C and decreased as salinity and temperature increased. Sequential stages of embryonic development were documented and several year classes of offspring were produced to form a captive breeding colony. We conclude that the giant kokopu has notable reproduction-related qualities that may be useful for future aquaculture exploitation of this species.

Conservation breeding of Shortfin eels Anguilla australis and Giant kokopu Galaxias argenteus at Mahurangi Technical Institute using aquarium and aquaculture techniques

Mahurangi Technical Institute (MTI) operates a commercial fish hatchery that conducts aquaculture research, acts as a teaching tool for aquaculture students, breeds native fish for reintroduction projects, and for supply to zoos and public aquariums for display, as well as breeding selected introduced species for biological control of aquatic weeds throughout New Zealand. This research arm has a long and successful history in the breeding and rearing of a number of fish species, including New Zealand native threatened freshwater‐fish species. The Shortfin eel Anguilla australis, Giant kokopu Galaxias argenteus, Banded kokopu Galaxias fasciatus, Shortjaw kokopu Galaxias postvectis, Koaro Galaxias brevipinnis, Redfin bully Gobiomorphus huttoni, Common bully Gobiomorphus cotidianus, Giant bully Gobiomorphus gobioides, Cran's bully Gobiomorphus basalis, Freshwater shrimp Paratya curvirostris and Freshwater crab Amarinus lacustris have all been bred successfully at MTI. Of these native species, MTI has successfully closed the lifecycle of Giant kokopu, Banded kokopu, Cran's bully, Common bully, Freshwater shrimp and Freshwater crab. This paper focuses on work so far conducted to close the lifecycle of the Shortfin eel and the Giant kokopu.

Ovarian biopsy: a non-terminal method to determine reproductive status in giant kokopu, Galaxias argenteus (Gmelin 1789)

AIM: To establish a method of gonad biopsy for ovarian tissue collection in the declining giant kokopu Galaxias argenteus (Gmelin 1789) as an alternative to lethal sampling in order to understand the species' reproductive biology. METHODS: Six female giant kokopu weighing between 200 and 350 g were caught from the wild in early December of 2009 and transferred to a holding facility (Department of Zoology, University of Otago, Dunedin) where they were kept under a simulated natural photo-thermal regime for 10 months. Fish were repeatedly biopsied for ovarian tissue at near-monthly intervals (mean number of days between biopsies = 33) until ovulation. RESULTS AND CONCLUSIONS: Ovarian samples were successfully collected from giant kokopu by biopsy for use in downstream analyses. Among a total of 23 biopsy events, a single death occurred when a two-layered suturing approach was used, highlighting the value of this method for study of the reproductive biology of valuable fish. CLINICAL RELEVANCE: This biopsy method may have implications for veterinary research on fish physiology, pathology, conservation and development, when repeated tissue samples need to be collected over a prolonged period of time or for general surgical manipulations on fish when accessing the coelom. Furthermore, this approach allows the implementation of a more powerful experimental design, as repeated measures reduces the variability of estimates due to the removal of inherent stage differences among individuals.