Greenback Flounder Rhombosolea Tapirina Research Articles

Reproductive biology and endocrinology of greenback flounder Rhombosolea tapirina (GÜnther 1862)

The relationship between patterns of gonadal development and endocrine changes during reproductive development was examined in the greenback flounder (Rhombosolea tapirina). Oocyte size–frequency distributions showed that female greenback flounder have group synchronous oocyte development, and that there are multiple ovulations. Plasma and ovarian concentrations of testosterone (T) and 17β-oestradiol (E2) were elevated in association with vitellogenesis. Plasma concentrations of 17,20β-dihydroxy-4-pregnen-3-one (17,20βP) were significantly elevated in ovulated females, whereas ovarian concentrations of 17,20βP were elevated in association with final oocyte maturation (FOM) and ovulation. Plasma concentrations of 17,20βP-sulfate but not 17,20βP-glucuronide were elevated in association with FOM and ovulation. Changes in macroscopic testis stage were not accompanied by significant changes in proportions of gamete types in the testis. Plasma concentrations of T were elevated in spermatogenic and partially spermiated males. No significant changes in plasma 11-ketotestosterone (11KT), 17,20βP, 17,20βP-sulfate and 17,20βP-glucuronide were detected with change in testis stage.

The effects of common laboratory and husbandry practices on the stress response of greenback flounder Rhombosolea tapirina (Günther, 1862)

This study examined the stress response of the greenback flounder Rhombosolea tapirina to common laboratory and aquaculture practices. Plasma levels of cortisol in wild fish sampled within 2 min of capture were comparable to plasma cortisol values in other species captured from the wild and sampled immediately. Plasma levels of cortisol were significantly higher in wild fish sampled after capture, confinement and transport. The latency of the plasma cortisol response to stress was approximately 10 min. Cultured greenback flounder, exposed to normal husbandry conditions, had low plasma cortisol levels; however, 3 h of crowding combined with 5 min chasing (simulated grading) resulted in significantly elevated cortisol levels for up to 48 h. Plasma cortisol was significantly higher in fish held at medium and high stocking density than at low density. The plasma cortisol stress response of greenback flounder is similar to that shown by other marine teleosts. Plasma lactate levels in wild fish sampled after capture, confinement and transport, were considerably higher than levels in fish sampled within 3 min of capture, or exposed to 30-min exercise. No significant changes in muscle lactate were observed in response to exercise; however, there were significant increases in plasma lactate, and muscle [H +] and a significant decrease in plasma [H +] following exercise, indicating that muscle and blood physiology of greenback flounder do change in response to exercise. Unlike other flatfish, there was little evidence for in situ glycogenesis within white muscle tissue after exercise and there was some indication that greenback flounder have higher aerobic scope than other flatfish studied to date. This study showed that some routine husbandry practices have the capacity to stress greenback flounder.

Restriction endonuclease analysis of atypical Aeromonas salmonicida isolates from goldfish Carassius auratus, silver perch Bidyanus bidyanus, and greenback flounder Rhombosolea tapirina in Australia

Restriction endonuclease analysis of atypical Aeromonas salmonicida isolates from goldfish Carassius auratus, silver perch Bidyanus bidyanus, and greenback flounder Rhombosolea tapirina in Australia

Spatial variation in feeding, prey distribution and food limitation of juvenile flounder Rhombosolea tapirina Günther

The feeding and prey distribution of juvenile greenback flounder Rhombosolea tapirina Günther was compared between Swan Bay, a sheltered bay with muddy sediments and a well-developed seagrass-detrital system, and an adjacent area of Port Phillip Bay, a more exposed area with coarser sandy sediments. Meiofauna was dominated by benthic harpacticoid copepods in both bays. Harpacticoids in Port Phillip Bay, however, were mainly interstitial while epibenthic species were dominant in Swan Bay. The diet of juvenile flounder in Swan Bay was almost entirely composed of epibenthic harpacticoids. Juvenile flounder in Port Phillip Bay ate epibenthic harpacticoids, harpacticoid nauplii and gammaridean amphipods; interstitial harpacticoids were apparently not susceptible to flatfish predation. In Swan Bay, there was a rapid increase in the number of prey consumed with fish size but the mean size of prey was constant, reflecting the size distribution of harpacticoids in the environment. At one site in Port Phillip Bay, the pattern was similar except that the increase in prey number with growth was much lower. At a second site, prey number decreased while prey size increased with increasing fish size, due to a replacement of harpacticoid nauplii with much lower numbers of gammaridean amphipods. Consumption of prey in terms of weight increased allometrically with fish size at all sites. The rate was significantly higher (80%) in Swan Bay, suggesting that fish in Port Phillip Bay were food-limited. Gut clearance times for juvenile flounder feeding on epibenthic harpacticoids was estimated to be ≈ 13 h. Feeding rate, in terms of prey number, was approximately three to four times higher in Swan Bay relative to Port Phillip Bay. Although abundance of juvenile flounder in Swan Bay was higher than in Port Phillip Bay, prey abundances were also much higher, and predatory impact was estimated to be insignificant. Impact of predation also appeared insignificant in Port Phillip Bay although more data are needed.

Comparative diets, prey selection, and predatory impact of co-occurring larvae of two flounder species

The dominant prey of small larvae of two pleuronectid flounder species, greenback flounder Rhombosolea tapirina Günther and long-snouted flounder Ammotretis rostratus Günther, were bivalve veligers, which were also the most abundant zooplankter in the environment. When large larvae of both species were collected together, the dominant prey of Rhombosolea tapirina was the cladoceran Evadne nordmanni Loven, while paracalanid copepodids were the dominant food of Ammotretis rostratus. The relationship between predator and prey size was similar for both species, with size of prey consumed increasing with larval growth. Smallest feeding larvae consumed larger prey ( x ̄ = 100 μm width) than most larvae of marine fish at this stage. Comparison of diets of flounder larvae with abundances of microplankton in the environment revealed strong selection for prey type as well as prey size. Similar distributions of Evadne nordmanni and paracalanid copepodids in microplankton samples indicated that divergence in prey selection by larger larvae was due to innate preference, rather than fine-scale co-occurrence with prey. From a knowledge of feeding period, average gut contents, and gut evacuation time, I estimated that flexion-stage Rhombosolea tapirina would consume ≈ 75 prey per day. I conclude that at levels of larval fish and prey abundance observed in Port Phillip Bay, Australia, flounder larvae would have negligible impact on prey populations.