Estuarine Fisheries Research Articles

Monitoring data poor small-scale estuarine fisheries: a proposal from the striped mullet (Mugil cephalus) fishery in the Rapel River, Chile

Chile has a relatively long history of monitoring and managing large-scale commercial fish stocks. However, many other small-scale fisheries, particularly those operating in estuaries, usually lack basic fisheries and biological information. International experience indicates that a monitoring system designed for large-scale stocks cannot simply be resized to address the complexity, relatively low total economic value, and the large number of actors and supply chains in small-scale fisheries. This article proposes a strategy to monitor data-poor fisheries operating in estuaries. The striped mullet (Mugil cephalus), locally known as “lisa”, in the Rapel River, central Chile, was selected to establish a pilot monitoring program for small-scale fish resources. From May 2022 to May 2023, fisheries information, including fleet description, catch and effort data, and fish biological attributes such as length and weight, were collected and described for the first time in the region. Drawing insights from this case study, we propose developing a generic monitoring system tailored specifically for monitoring fish stocks in estuaries. This conceptualization is based on: i) change agents, who are individuals trained to work with both the social and biological dimensions of each coastal fish stock; ii) experienced fisheries scientists outside government agencies; and iii) local fishers' knowledge to provide constant feedback for adapting temporal and spatial scales for monitoring. This monitoring scheme is cost-effective and can be efficiently replicated in other estuarine fisheries in Chile.

Boosting spring runoff into the sea by reservoir regulation and its potential for estuarine fishery recovery

Boosting spring runoff into the sea by reservoir regulation and its potential for estuarine fishery recovery

Delineating the fish-based ecosystem services of a small tropical Indian estuary: Identification, evaluation and management

In this study, we evaluate the fish-based ecosystem services (ES) of Chettuva, a small tropical estuary (CE) on the south-west coast of India. Besides the direct benefits (provisioning and cultural), the primary regulatory and supporting services provided by fish in estuaries were also documented using secondary data and focused group discussions (FGD). The major obstacles impeding the fisheries-based ES were also identified, and priority-based management options were proposed. The annual economic value of the major fish-based ES of the estuary was estimated to be ₹814.55 million (₹36.96 million for provisioning, ₹569.52 million for supporting, ₹177.6 million for regulating and ₹30.47 million for cultural and information services including recreation, tourism, scientific and information services, respectively). The estuarine fishery in CE is still traditional, employing non-motorized boats and supporting the livelihood of about 300 active fishers. Our findings revealed that stakeholders rated higher values on provisioning, supporting, and cultural services while providing little significance on the regulating services. The current findings indicated that, as the primary means of livelihood, fisheries not only provide a pragmatic overview of the economic value of estuarine systems but also signifies the use of fisheries-based ES as a valuable tool in developing an ecosystem-based management plan. Based on the findings, it would be reasonable to highlight the need for ES-based approach for resource conservation in fisheries management of the small tropical estuaries.

Biological processes in seagrass beds of coastal lagoons to maintain estuary-dependent marine fisheries

Following the planned FAO Ecosystem Restoration Programme for estuarine habitats to support estuarine fisheries and early life stages of estuary-dependent marine fish, direct relationships of total seagrass and eelgrass Zostera m. capricorni areas and biomass with fish harvest were derived for a range of slightly to highly urbanized coastal lagoons that are expected to support the larvae and juveniles of estuary-dependent marine fisheries. Fish harvest and seagrass area and biomass in the lagoons increased with moderate catchment total suspended sediment and total phosphorus loads due to lagoon flushing rates directing excess silt and nutrients out to sea via the lagoon entrances. Well managed, sewered catchment management works are shown that could assist estuary managers maintain seagrass for estuarine and offshore estuary-dependent fisheries by maintenance of seagrass and fishery ecological processes. Further research is suggested to investigate estuary-dependent post-juveniles leaving estuaries and lagoons migrating to nearshore, offshore and shelf marine fisheries.

Differences in Recreational Fishers’ Motivations for Utilising Two Estuarine Fisheries

Effective fisheries management requires an understanding of human dimensions. This study elicited the salient motivations for recreational blue swimmer crab and black bream fishing in Western Australia and whether these views differed depending on the fishing location and/or the characteristics of the fisher. Crab fishers were strongly consumption-orientated and aimed to “catch big crabs” and “catch enough crabs to eat”. Furthermore, 91% consumed their catch, with only 2% practicing catch-and-release fishing. In contrast, 81% of black bream fishers did so for the sport/challenge, with the strongest motivation being to catch a bream considerably above legal size and with food only selected by 15% of respondents; most fishers released caught fish. The marked differences between the fisheries for the two species, which co-occur in the same estuaries, are likely driven by the accessible nature of the crab fishery, ease of catching crabs, the low cost of fishing equipment, and their taste. Fishing for black bream, however, requires more expensive equipment, patience, and a greater skill level. Fishers considered crabbing to be as important as other fishing and outdoor activities, whereas bream fishers considered bream fishing considerably more important, reflecting the trophy nature of this fishery.

Spatial management of estuarine fisheries resources: Do recreational-only fished estuaries provide conservation to harvested species?

Spatial management of estuarine fisheries resources: Do recreational-only fished estuaries provide conservation to harvested species?

An extreme climate event and extensive habitat alterations cause a non-linear and persistent decline to a well-managed estuarine fishery

An extreme climate event and extensive habitat alterations cause a non-linear and persistent decline to a well-managed estuarine fishery

Mapping essential habitat of estuarine fishery species with a mechanistic SDM and Landsat data

The identification and monitoring of essential fishery habitat (EFH) is primary and important for the conservation of estuarine fishery habitat and sustainable fisheries management. However, mapping EFH of estuarine fishery species with generally statistical species distribution model (SDM) remains difficult due to their complex life histories and the extensive spatiotemporal variability of habitat variables. Thus, we proposed a mechanistic SDM by analyzing a more direct and certain relationship at a pre-selected suitable life stage with prior knowledge of species life history, not a rough statistical analysis of overlapping cause–effect relationships operating across multiple life history stages in reverse. Landsat data was used to describe the extensive spatiotemporal variability of estuarine habitat variables. A window filtration was contributed most to select the suitable life stage with a score scheme. As mapping EFH needs to feasibly locate the representative and essential habitats over large estuarine scale, we constructed two indicators to represent “habitat importance” and “descriptor predictability” in the score scheme, which was semi-quantified with three primary factors (habitat function, duration of life history stage, inversion limitation of critical descriptors from Landsat data). Through selecting the suitable life stage for the mechanistic SDM, the usage of Landsat archives could be extended, which is beneficial from a few optically / thermally active determinants. The applicability of the mechanistic SDM was tested by mapping EFH of Eriocheir sinensis in the Yangtze River Estuary (YRE), China. The window filtration of E. sinensis’ life history stages in the YRE showed that the berry stage was filtered as the suitable stage with the highest scores both in habitat importance and descriptors predictability. Then the distribution of E. sinensis was modelled, predicated, and assessed at berry stage by comparing outward in a generally statistical way and inward with other filter window. The mechanistic model at berry stage showed the best explanatory and predictive power in both occurrence and abundance models, validating that the optimized SDM had much stronger capability in model fit and prediction. The score scheme was also verified to set reasonably and effectively through the model comparisons at different filter window stages. With the predicated distribution of E. sinensis, the core ranges of EFH were mapped at berry stage, which were mostly distributed in sub-tidal areas neighbored to wetlands, showing the habitat requirement of shallow water for hiding. Meantime, the determinants’ variance partitioning, in which dissolved oxygen (DO) and total suspended sediment (TSS) exceeded over 65%, complementally illustrated that core EFH may also require high water quality. The identification of EFH locations with our mechanistic SDM would provide spatial-explicit information and guidance to fishery habitat protection and fishery resources maintenance. Additionally, this study also explored a new way to utilize a few predictors from the extensively used Landsat data in an alternative way. This study could extend the limitations of SDM in EFH mapping and bridge gaps between spatiotemporal explicit modelling and remote sensing data accommodations, which is meaningful for fishery habitat conservation.

Estuarine Ichthyoplankton Studies – A Review

Estuaries are nutrient-rich environments with a gradient of fresh to salt water. They support high primary productivity and an abundance of zooplankton. Estuaries are used by many fish as nursery grounds because their environmental conditions provide abundant food for larval and adult fish. Ichthyoplankton, which comprise fish eggs and larvae, are important for the recruitment of fish species. At present, there are no systematic reviews on ichthyoplankton in estuaries from a global perspective. Here, research on ichthyoplankton over the last 60 years (1951–2022) was reviewed, focusing on three aspects: evaluation of ichthyoplankton published studies, community structure, and factors affecting community structure. The results show that research on estuarine ichthyoplankton has increased, from less than 1 article per year in the 1950s to more than 30 articles per year in the 2020s. The keyword used most commonly was ‘community structure’ and ‘dynamics’ and the word used most recently was ‘climate change’. Regarding the geographical distribution of the studies carried out on estuarine ichthyoplankton, USA had the most (32.9% of all studies), followed by Australia (8.1%), South Africa (6.1%), Brazil (5.6%), Japan (5.1%), China (4.9%), Canada (4.8%), and Portugal (4.8%). Salinity and turbidity were the main factors affecting the ichthyoplankton community structure in estuaries. Climate change indirectly affected the community structure of estuarine ichthyoplankton by changing the spawning time, spawning location, and hatching time of species. The movement of spawning sites poleward and the advance of spawning time showed a consistent trend. In addition, the development of DNA barcoding techniques will be a useful supplement to traditional taxonomic methods for identifying ichthyoplankton and will provide new opportunities for the development of systematic taxonomy in this field. Our review contributes to a broader understanding of estuarine ichthyoplankton and provides theoretical support for estuarine environmental protection and the sustainable use of estuarine fishery resources.

Socio-ecological change in the Ruvu Estuary in Tanzania, inferred from land-use and land-cover (LULC) analysis and estuarine fisheries

Ecosystem goods and services derived from estuaries have sustained coastal livelihoods in the Western Indian Ocean (WIO) region throughout recorded history. Estuaries provide fertile and seasonally irrigated space for planting crops, mangrove products for construction and fuel, and fish as a protein source. Human population growth and an escalating demand for natural resources threaten estuarine critical habitats and their functioning, exacerbated by the effects of climate change. Decadal and seasonal land-use and land-cover (LULC) changes in the Ruvu Estuary in Tanzania were investigated through analysis of Landsat 5/8 and Sentinel-2 satellite images. The estuary is river-dominated and truncated near the coast during high river flow, with tidal influence extending approximately 12 km upstream during low river flow. LULC change detection targeting nine classes (water, developed, barren, forest, grasslands, cultivated, mangroves, wetlands and mudflats) showed that estuary-associated wetlands and mangroves had declined significantly over the past two decades (1995-2016) making way for developed land (growth of Bagamoyo Town), cultivated land (agricultural expansion with increasing population) and grasslands (coastal habitat changes). Seasonal LULC changes were conversion of wetlands to cultivated land after the wet season, and transformation of fallow wetlands to grasslands. The estuarine fishery relied on a small number of mainly freshwater and marine migrant species, compared to a highly diverse mix of mainly marine species in the nearby coastal fishery. The sparsity of quantitative fisheries data, spectral confusion when modelling land-cover change, and absence of household survey data to assess livelihood activities remain major information gaps. Generalized recommendations for improving socio-ecological change studies in WIO estuarine systems are provided.

Small-scale fisheries of the Bons Sinais Estuary in Mozambique with emphasis on utilization of unselective gear

Small-scale fisheries in estuaries of the Western Indian Ocean form a key component of socio-ecological systems (SES) and food security, yet they remain poorly understood. This study describes the estuarine fisheries of the Bons Sinais Estuary in Mozambique based on fisheries and biological data collected by monitors between 2007 and 2016. Multiple gears were used, including beach seines (78 % of sampled fish), chicocota nets (12 %), gillnets (5 %), and hook and line (4 %). Landings were dominated by small pelagic fishes (Engraulidae 29 %, Pristigasteridae 16 %, Clupeidae 11 %) and prawns (Penaeidae 29 %). Monthly averaged fishing effort, landings and catch per unit effort of beach seine and chicocota nets peaked during the dry season, in April and July to October. The proportion of penaeid prawns in landings increased moderately at the end of the wet season, between January and March. The species and size composition selected by beach seine and chicocota nets overlapped, with chicocota nets also retaining marginally smaller individuals. Both gears exploited low trophic level species near the base of the food web, with low trophic values of 2.8 for chicocota and 3.0 for beach seine nets. The small-scale fishery in the Bons Sinais Estuary followed a ‘balanced harvest’ approach in which unselective fishing gear is used to exploit a mix of species and sizes proportional to natural productivity and relative abundance.

Small-scale fisheries of the Tana Estuary in Kenya

The role of small-scale fisheries in maintaining socio-ecological systems (SES) in the Western Indian Ocean is well-documented, yet few studies have addressed estuarine fisheries in the region. Small-scale fisheries in the Tana Estuary in Kenya are described in this paper, accounting for location along a salinity gradient, seasonality, gear types used, species composition and relative abundance of landings. Monthly shore-based sampling was undertaken at four locations in 2017 – Ungwana Bay near the estuary mouth, lower and mid-estuary, and upper estuary at Ozi village, ⁓10 km upstream. Fishing gear comprised of seine nets, gillnets, hook-and-line and traditional gear such as self-made traps, sticks and spears operated from the shore (foot fishers), dugout canoes, dhows and fibreglass boats with outboard engines. A total of 12,840 fish and crustacean specimens belonging to 89 species in 45 families were sampled. Landings were dominated by catfishes Arius africanus (31 %) and Clarias gariepinus (21 %), small pelagic fishes Pellona ditchela (10 %) and several sardine species (⁓5 %), croaker Otolithes ruber (10 %), eel catfish Plotosus limbatus (6 %), mullet Mugil cephalus (4 %) and Nile tilapia Oreochromis niloticus (4 %). Multivariate analyses (nMDS and ANOSIM) found that fishing gear (p < 0.05) and location (p = 0.001) significantly influenced catch composition, but season (p = 0.146) was not significant. Traps were used in the upper and mid estuary only and were selective for three catfish species. Seine nets (54 species) and gillnets (40 species) were least selective and used at all four locations. Rarefaction curves indicated that species diversity was higher at the bay and lower estuary than the mid and upper estuary, and that diversity was highest for canoe-gillnet and canoe-encircling net combinations. Catch rates (avg. of 2.3 to 8.4kg.fisher-1.day-1) depended on gear type and was highest for monofilament gillnets. Catches comprised a broad size range of multiple species, but on average, seine nets selected smaller individuals than traps, gillnets and long lines. The high complexity and organization of the fishery at an estuary-scale makes it a good example of a relatively intact SES suitable for regional comparative analyses.

Coastal winds and larval fish abundance indicate a recruitment mechanism for southeast Australian estuarine fisheries

AbstractCoastal winds transport water masses and larval fish onshore or offshore which may influence estuarine recruitment, yet our understanding of the mechanism underlying this relationship is limited. Here, we combine datasets from a historical database of larval fish off southeast Australia with a high‐resolution atmospheric reanalysis model to show that normalised abundance of coastally spawned larvae increased with weak to moderate upwelling favourable winds 14 days prior to sampling. The increase in abundance may reflect increased nutrient and plankton availability for larval fish. Normalised larval abundance decreased following strong upwelling favourable winds but increased after onshore (downwelling favourable) winds, due to wind‐driven transport. By combining a commercial estuarine fisheries catch‐rate dataset (4 species, 8 estuaries, 10 years) and the high‐resolution atmospheric reanalysis model, we show that negative effects of upwelling favourable winds during the spawning period can be detected in lagged estuarine commercial fisheries catch rates (lagged by 2–8 years depending on species' growth rates), potentially representing the same mechanism proposed for larval fish. Upwelling favourable winds in the southeast Australian region have increased since 1850 while onshore winds have decreased, which may have reduced larval recruitment to estuaries. Coastal winds are likely an important factor for estuarine recruitment in the southeast Australian region and future research on the estuarine recruitment of fish should incorporate coastal winds.

Applying systematic conservation planning to improve the allocation of restoration actions at multiple spatial scales

Ecological restoration is increasingly being upscaled to larger spatial scales of tens to hundreds of kilometers. Yet the complex logistics and high costs of ecological restoration mean that actions must be placed strategically at local scales of tens of meters to maximize ecological benefits and reduce socioeconomic costs. Despite the purported use of systematic planning tools for allocating restoration effort, the uptake and implementation of data‐driven restoration planning and ecological goal setting remains poor in many restoration programs. Here we demonstrate how the sequential workflows of systematic conservation planning can be translated to restoration at two spatial scales to enhance estuarine fisheries in eastern Australia. We select estuaries where restoration is feasible and recommended based on quantitative regional ecological goals (i.e. regional‐scale prioritization), and then identify potential restoration sites at smaller spatial scales within estuaries based on the principles of spatial ecology to ensure that the success and benefits of restoration are maximized (i.e. local‐scale prioritization). At the regional scale, we identified four levels of restoration priorities (very high, high, intermediate, and low) using quantitative ecological goals and the current ecological understanding of each system. At the local scale, we used spatially explicit Bayesian belief networks to identify sites that maximize restoration outcomes based on the environmental niche of habitat‐forming species and the spatial configuration of habitats that maximizes their use by fish. We show that using systematic frameworks can become an essential tool to optimize restoration investments at multiple scales as efforts upscale globally.

Socioeconomic and productive marine and estuarine fishery activity potential index

Considering the need for increased productivity, consequently providing a safe source of quality food and economic sustenance for numerous families, fishing in the State of Rio de Janeiro is configured in an important way, and with a primarily artisanal and professional nature of small bearing. In addition to the fundamental aspect of human subsistence, fishing is an important economic activity, generating several other businesses and income for other economic sectors, such as transport, storage, processing and sale of products, construction and repair of vessels, and construction of artifacts and utensils, among others. Thus, the study of potentialities and vulnerabilities involving the strengths and weaknesses of the coastal region of Rio de Janeiro will assist in actions in favor of a broad development of activity in the coastal municipalities. For this, the analytic hierarchy process was used, a multicriteria analysis method, to construct hierarchies of these municipalities in terms of potential development, and thus the analysis of the environment was performed using a matrix to analyze the scenarios. The results point out that due to the importance accorded by the interviewees to the economic sub-index, the municipality of Angra dos Reis stood out in the order of priority of defining the municipality with the highest socioeconomic and productive potentiality index for fishing activity, presenting quantitative data related to sub-indices of greater importance than the other municipalities. However, when the analysis for each subscript was carried out separately, Angra dos Reis has the lowest classification for vulnerability to environmental and social issues.

Diversity, density, and Importance Value Index of mangroves in the Segara Anakan lagoon and its surrounding area, Cilacap Regency, Indonesia

Coastal mangrove forest habitats in the Segara Anakan Lagoon have become an important area for estuarine fisheries which should be preserved for sustainability. This study aims to analyze diversity, density, and the importance value index of the mangrove in the area. The method used was a plot and path (combination method). To conduct this study, the nine purposely sampled stations ranged from the western Segara Anakan Lagoon to the eastern mangrove area adjacent to the Donan River. The nine station was grouped into 3 (three areas) namely; Mangrove Eastern Area (river influence), Mangrove Middle Area, Mangrove Western Area (seawater influence. The results show the average mangrove density overall stations were dominated by seedlings with 39881 individuals/ha with fraction 75%, followed by saplings with 12311 individuals/ha (23%), and tree category with 711 individuals/ha (1%). Because of the average mangrove density of tree category less than 1000 trees/ha so, the mangrove forest in the Segara Anakan Lagoon and its surrounding area was categorized to be damaged. Meanwhile, the highest Importance Value Index (IVI) was at 221 for R. apiculata and at 220 for Sonneratia caseolaris for all stations.

The Socio-ecological System of Urban Fisheries in Estuaries

Fisheries and urban marine ecology meet within the world’s densely populated estuaries and coasts, where the imperative of dredging, construction and catchment modification occurs alongside the socio-economic characteristics of urban communities. Estuarine fisheries in urban areas have often shifted away from commercial harvest towards recreational fishing, fuelled by a diverse range of motivational factors. These systems are thus often dominated by recreational and subsistence fisheries, with the fisheries system variously impacted by eutrophication, contamination and pollution, altered trophic structure, habitat loss and hard structure. Urban marine ecosystems may be distinguished by the absence of spawning by exploited finfish, coupled with the gradual loss of environmental signals for recruitment, reduced larval supply and loss of nursery habitats for juveniles, but alongside an abundance of hard structure habitats for adults. The shift from commercial fishing to preferential harvest of more predatory “sportfish” means that the historical trophic structure has shifted towards lower trophic levels (e.g. prawns, detritivores, planktivores). We outline urban estuarine fisheries ecology as a developing paradigm defined by the unique ecological attributes of urbanised estuaries, the socio-economic objectives of fishers therein, and bottlenecks to productivity of the species they exploit. We identify goals for future research and management and illustrate these concepts through discussion of stock enhancement with a large estuarine predatory fish.

Physiological stress response and recovery of an important estuarine fishery species, dusky kob Argyrosomus japonicus, after a simulated catch-and-release event

Catch and release (C&R) angling is a popular pastime the world over; however, studies have found that fish can experience considerable stress during a C&R event. To determine the effect of a C&R event on angled fishes, the physiological stress response (PSR) is often assessed. However, the peak PSR only occurs after a delay and is species-specific. The dusky kob Argyrosomus japonicus is a threatened species that is heavily exploited in South African estuarine fisheries. Given its collapsed-stock status, it is critical to understand the effects of C&R angling on the PSR of this species. The aim of this study was to plot the time-course of the PSR of A. japonicus to determine when the peak PSR occurs. Time had a significant effect on blood lactate (p < 0.05) and glucose (p < 0.05) levels, with both peaking 30–40 minutes after a stressor, but time did not have a significant effect on plasma cortisol levels (p > 0.05). Blood lactate and glucose levels reached recovery by 150 minutes. The results suggest that blood sampling should be done 30–40 minutes after a stressor, and although A. japonicus is able to recover quickly from a C&R event, its delayed PSR may render it vulnerable to post-release predation.

Assessing the vulnerability of small-scale fishery communities in the estuarine areas of Central Vietnam in the context of increasing climate risks

Although Vietnam's coastal and estuarine areas are most vulnerable to the impact of climate shocks, very few studies have closely evaluated this vulnerability. This research applied the Livelihood Vulnerability Index (LVI) and the United Nations Intergovernmental Panel on Climate Change vulnerability framework (LVI-IPCC) to estimate the climate vulnerability of small-scale fisheries in the Tam Giang – Cau Hai lagoon, Central Vietnam - recognised as the biggest brackish water lagoon in South East Asia. Mixed methods, including key informant interviews, group discussions and questionnaire surveys (N = 181), were applied to collect empirical data in two estuarine fishery communities of Loc Binh and Huong Phong communes, Thua Thien Hue province. Two important findings emerge from this analysis, (1) the overall results of this study indicate that livelihood strategies and availability of food are the most critical factors in determining livelihood vulnerability for the two surveyed communes in the TG-CH lagoon and (2) the LVI and LVI-IPCC are effective tools to assessing vulnerability at the community level. It is expected that the lessons learnt from this study will assist in designing future studies and help devise intervention strategies to reduce the vulnerability of small-scale fishery communities in developing countries.

Reproductive development of the priapium fish Neosthetus lankesteri Regan, 1916 (Atheriniformes: Phallosthethidae) from Pranburi river estuary, Thailand using the histological approach

Reproduction in the family Phallostethidae is an area that has long been of interest especially in gonadal structure and gametogenesis. However, no published data concerning as mentioned above in Neostethus lankesteri Regan, 1916 from Thailand is noted. This fish is important for rural livelihood in the estuarine fisheries of Pranburi River estuary, Thailand. The construction of the female reproductive system of N. lankesteri composed of the ovary and short oviduct. The mature ovarian morphology is a single organ, which is histologically considered to be an asynchronous development ovary. The differentiating oocytes were observed and classified into oogonia proliferation, primary growth phase, secondary growth phase, post-ovulatory phase and atretic follicle phase. Under the ovarian differentiation, our observation indicated that the ovarian parenchyma of N. lankesteri during 1.8 – 2.4 cm in standard length (SL) was accompanied by the secondary growth phases. Identification of the post-ovulatory phase was detected during our sampling periods, indicating to entire life in the Pranburi River estuary as well as true resident species. In the male reproductive system of N. lankesteri, the mature testicular parenchyma was organized morphologically as a single organ and histologically appeared to be a restricted spermatogonial lobular testis type. The differentiation of the spermatogenetic stage was composed of three phases including spermatogonial, spermatocyte and spermiogenetic phases. It was to identify possible trends that the size at first maturity of the female fish was estimated at 1.8 cm SL. Certainly, results from this study clearly showed on the reproductive pattern of N. lankesteri, which could be applied to further studies (the reproductive cycle, spawning season and histopathology).