Rearing of Bitterling (Rhodeus amarus) Larvae and Fry under Controlled Conditions for the Restitution of Endangered Populations

Among the several dozen European freshwater fish species, only European bitterling (Rhodeus amarus Bloch) and Rhodeus meridionalis belong to the group of ostrakophilous fish. The embryonic and larval development of the fish in this reproductive group until the time of the yolk sac resorption takes place in the gill cavity of river mussels (Anodonta sp. or Unio sp.). This paper presents the results of the European bitterling Rhodeus amarus being reared under controlled conditions. Bitterling larvae were caught together with river mussels in the natural environment and subsequently placed in a tank for behavioural observations. Bitterling larvae were seen swimming in the water within a week of placing the bivalves under controlled conditions. The bitterling larvae were 8.6 ± 0.11 mm long when they started to swim actively. The rearing was conducted in water at 20 and 26 ± 0.5 °C and lasted for 6.5 months (200 days) in both variants. Initially, the larvae were fed with live nauplii of Artemia salina and subsequently with fodder. The bitterlings in tanks with water at 26 ± 0.5 °C were 66.2 ± 3.0 mm long and weighed 3389 ± 548 mg. For comparison, bitterlings kept in water at 20 ± 0.5 °C were 64.48 ± 3.4 mm long and weighed 3242 ± 427 mg. No larval malformities or mortality were observed during the larvae and fry rearing. The bitterlings had well-developed secondary sexual characteristics and exhibited pre-spawning behaviour at the end of the rearing. This produced suitable bitterling stocking material to be used in the conservation of small or endangered populations.

Saltwater spawning grounds of sea-run brown trout (Salmo trutta) in tidal waters of a major Norwegian river

Sea-run brown trout (Salmo trutta) have a highly phenotypically plastic life history that allows them to be effective colonizers and competitors in freshwater. This paper documents a previously unknown spawning behaviour in a brackish, tidally influenced estuary 14 km from the mouth of the Vosso River, a major Atlantic salmon- and sea-run brown trout–producing river in western Norway. Putative spawning gravel was observed, and sea-run brown trout deposited eggs that hatched in April. Survival of recruits was high (> 95%) in the tidal spawning gravel. These areas are strongly tidally influenced with a peak of 23.17 psu recorded at the lowest spawning ground. The observation of spawning so far from the river mouth may be unique in such a system with a long estuary but provides important insight into the biology of sea trout. Invasion of pink salmon, also known to spawn in estuaries, may negatively affect the competitive balance of sea trout with other salmonids in rivers where sea trout populations rely on recruitment from these relatively extreme spawning areas. Restoration of estuaries that have been modified by dredging or channelization may be important to ensure quality and heterogenous habitat for sea trout spawning given that haline spawning grounds could contribute to population resilience.

Field observations on the behavioural ecology of the stout bobtail squid Rossia macrosoma (Cephalopoda: Sepiolidae) from Scottish waters

Bobtail squids (Cephalopoda: Sepiolidae) are emerging model organisms for a wide range of genetic, anatomical, neurophysiological and behavioural studies. However, the knowledge about their behavioural ecology is scarce and derives mainly from laboratory-based studies, whereas observations from the wild are rare. Here, we use photo and video footage collected through the Cephalopod Citizen Science Project to describe the hunting, burying, mating and spawning behaviour of the stout bobtail squid Rossia macrosoma (Delle Chiaje, 1830) from Scottish waters. Based on our long-term observations, we were able to determine a spawning period from August to November based on different behavioural traits for this species. Furthermore, we observed R. macrosoma to be able to adhere a sand grain layer (‘sand coat’) to its dorsal mantle. This behavioural feature has only been reported for two genera of the sepiolid subfamily Sepiolinae so far, and therefore represents the first of this kind for the subfamily Rossiinae. Lastly, we identified a local sea urchin species as an active predator of egg batches of R. macrosoma and discussed the cryptic egg laying behaviour of this bobtail squid species in terms of its protective traits to avoid egg predation.

Wild and farmed burbot Lota lota: differences in energy consumption and behavior during the spawning season

Farmed fish released in a native environment can display different spawning behaviour compared to their wild conspecifics. In our study, farmed and wild burbot, a species recently introduced for aquacultural production, were equipped with electromyogram (EMG) radio tags. EMG biotelemetry allows a description of the spatial distribution of fish together with simultaneous measurements of individual energy consumption. Farmed burbot were released into the wild to simulate stocking or hatchery escape and were observed over a nocturnal phase during November to January. The observational period was assumed to cover the whole spawning season, including an expected peak of spawning activity determined according to egg production by naturally spawning burbot in an experimental seminatural river channel. We detected increased energy consumption and lower movement activity at the time of expected peak spawning for wild burbot only. Across the whole spawning season, farmed females showed lower movement activity and energy consumption than wild females, whereas the opposite results were found for farmed males. Farmed and wild fish kept larger distances between each other than the individuals within a group (farmed and wild) across the whole spawning season. The closest positions occurred between males and females in the wild group, while for farmed fish, the closest position was found within the same sex. Sexually conditioned energy consumption and spatial distribution differed between wild and farmed fish.

Maturation Biology and Spawning Ethos of A Hillstream Loach Lepidocephalus Guntea (Ham-Buch) From River Mandal, Pauri Garhwal, Uttarakhand

The paper deals with studies on maturation biology and spawning behaviour of an important hill stream loach Lepidocephalus guntea (Ham-Buch) from river Mandal in District Pauri Garhwal Uttarakhand. It was observed that there was a continuous growth of ova throughout the year. Seven maturity stages in the fish were observed with single mode each month. Gonado-somatic index (GSI) and Dobriyal Index (DI) were calculated to find out the month of peak maturity, spawning frequency and spawning season. It was confirmed by tabulation of fishes in different maturity stages each month and also by physical observations in the field. It was concluded that June was the month of peak maturity and spawning takes place during July- August. Rare spawning was seen even in First week of September. Size at first maturity was 60-61 mm.

Reefing Viability Index for Rigs-to-Reefs (R2R) in Malaysia

Decommissioning of the offshore platform as an artificial reef, known as Rigs-to-Reefs (R2R), has become a sustainable approach for oil companies. The platform was reused to serve the underwater ecosystem as an artificial reef for a new marine ecosystem which helps to tackle food security issue. This paper presents the findings of the formulation of the reefing viability index to recognize an offshore region that can be used for R2R projects within the South China Sea. The combined effects of spatial data, numerical modelling, and geographic system (GIS) are proposed to study the relationship of spawning ground coral reefs, diversity, and planula larvae in the process of colonization to establish a map of the reef potential environment. Coral connectivity and spawning behaviour were studied to determine the possible source of coral seedling released during the spawning season, twice a year. A geographic reef viability index was established consisting of seven parameters which are coral larval density, pelagic larval length, sea currents, temperature, chlorophyll-a, depth, and substrate availability. The ocean hydrodynamic model was designed to resemble the pattern of larval scattering. By using the simulations and rankings, there were 95 (21%) sites which could probably be used for in situ reefing, whereas 358 (79%) sites were likely ideal for ex situ reefing. Validation of the viability index was carried out using media footage assessment of remotely operated vehicle (ROV).

Nests placements and spawning in the endangered horseshoe crab Tachypleus tridentatus (Leach, 1819) (Merostomata: Xiphosurida: Limulidae) in Sabah, Malaysia

Horseshoe crab populations are declining worldwide, and Tachypleus tridentatus (Leach, 1819) has recently been classified as Endangered in the IUCN Redlist. Among the keys for species survival is successful reproduction. Although there are reports on the reproduction, particularly details on the spawning behaviour, of the American species, Limulus polyphemus (Linnaeus, 1758), information on Southeast Asia species is very scant. This field study reports the nesting activities of T. tridentatus at Jambongan Island, Sabah, Malaysia. Observation were carried out on 16 spawning pairs that were spotted during full and new moon from April-July 2016 in Sabah. Nest placements, number of nests, number of eggs, time spent at each nest, and nest widths, depth, and distance from the highest tide line were recorded for each pair. Tachypleus tridentatus generally laid an average of 967 ± 54.1 eggs/nest (171–2,282) in as many as nine nests on the intertidal zone between 125 and 940 cm from the highest tide. The first nest was dug once the tide began rising, followed by the consecutive nests towards the highest tide line with nest depths ranging between 13 and 22 cm. The complete spawning session (first nest to the last) ended in less than two hours. Time spent in spawning correlates positively with the number of nests and the total number of eggs laid by each spawning female. The spawning area, which is made up mainly by fine and medium-size sediment grains, also experience stable temperature, salinity, and dissolved oxygen conducive for egg-laying and larval development for successful reproduction. The details of spawning are important for planning successful future conservation initiatives for the species, especially in tropical regions.

Trends in the size and age structure of marine fishes

Size-selective harvesting is expected to reduce the average age and weight of commercially exploited fishes. The loss of larger, older fish has been hypothesized to negatively affect metrics of population viability, such as spawning behaviour, recruitment, and adult survival. Most studies to date have focussed on individual stocks. Here, we examine trends in average age and weight at broad taxonomic and temporal scales, using subsets of data compiled on 95 marine fish stocks. Following moderate declines between 1960 and 1990, we find that the average age has generally increased since 2000, such that 71% of 69 stocks are currently above their long-term average. However, the size of the oldest individuals has generally declined over time; the average weight is currently below average in 75% of 55 stocks. A temporal decline in the mean weight of the youngest constituents within 49 stocks is most evident in the Clupeiformes. Our results indicate that recovery of age structure need not be accompanied by recovery of weights-at-age, evidenced in part by a decline in the size of the oldest individuals within populations. Further study into the drivers of these patterns, and the consequences of declining weights-at-age for population viability, is warranted.