Influence of hatch duration and individual daily growth rates on size structure of age-0 smallmouth bass cohorts in two glacial lakes

Abstract –  We assessed hatch dates and daily growth rates of age-0 smallmouth bass from two glacial lakes over a 3-year period. Hatching durations (19–27 days among years) of smallmouth bass occurred from late May until late June. Mean daily growth rate of age-0 smallmouth bass ranged from 0.56 to 1.56 mm·day⁻¹. Correlation analysis indicated that hatch date had little effect on daily growth rates. Hatch date was significant in explaining variation in total length (TL) of age-0 smallmouth bass at time of capture in only three of six cases and hatch date never explained >50% of the variation in bass length. Daily growth rate significantly explained variation in smallmouth bass TL at time of capture in all six models, accounting for 31–86% of the variability in bass length. Our findings suggest that size structure of age-0 cohorts in some populations may be more strongly regulated by variation in individual daily growth rate than by hatch timing.     

Ontogenetic diet shifts of age-0 smallmouth bass (Micropterus dolomieu Lacepède) in the New River, West Virginia, USA

Larval and juvenile smallmouth bass (Micropterus dolomieu Lacepède; 8.5–85.0 mm total length (TL)) were collected from 2 sites in the New River, West Virginia, in the late spring and early summer to document diet shifts during early ontogeny. The first foods of smallmouth bass (TL = 9 mm) were primarily Chironomidae and microcrustaceans (primarily Copepoda). Other aquatic insects, primarily Ephemeroptera, became more abundant in the stomachs as TL increased. A shift in the proportions and types of prey consumed began at approximately 15 mm TL and was primarily attributed to fin development and increased mouth size. Foraging success, measured by number of prey per stomach, stomach fullness, and average prey volume was lower for first-feeding smallmouth bass than for later life stages. Mouth width appeared to restrict the size of prey consumed by larval smallmouth bass, but the maximum prey width never approached the mouth width for fish longer than 35 mm TL.     

Larval Rearing and Weaning Techniques for White Bass Morone chrysops

The effects of culture parameters of tank color and feeding regimes were examined on larval white bass Morone chrysops during 1994–1995. Under high surface illumination (998 lux), dark tank walls were essential for effective prey capture. Larvae reared in clear glass aquaria did not grow and had died by day 6 of the study. In contrast, 48.7% of the larvae reared in black-walled tanks were alive on day 24 and had grown to 17.2 mm total length (TL). In another study, larvae were fed rotifers Brachionus plicatilis and Artemia nauplii in different feeding protocols. In one treatment only rotifers (10/mL) were fed day 1 (4 d post-hatch), rotifers and Artemia (3/mL) were fed days 2–4, and Artemia fed days 5–15. This protocol produced similar growth (mean size 11.7 mm TL) and survival (mean 30.3%) as slower weaning times from rotifers to Artemia . Juveniles (27-day-old, 17.2 mm TL) were converted to a dry crumble diet over a 14-d period by slow transfer from a combination diet consisting of live Artemia nauplii, frozen adult Artemia , plankton flakes and dry crumbles. Survival offish weaned to the dry diet was 64.5%. Most of the mortalities during the weaning period were fish with uninflated swim bladders which were cannibalized by larger fish. Using the above tank culture techniques, white bass were reared to a mean size of 73.2 mm TL (mean weight 5.8 g) over a 73-d period. This essentially closes the life cycle of white bass.     

Competition between hatchery‐raised and wild brown trout Salmo trutta in enclosures – do hatchery releases have negative effects on wild populations?

Abstract –  We compared the growth and prey consumption of juvenile hatchery and wild brown trout of similar genetic origin in 12 wire mesh cages in a natural river in North-Eastern Finland. Wild trout started feeding shortly after the start of the experiment, and clearly earlier than novel hatchery trout, but ate less in the presence of hatchery trout. When accompanied with wild trout, novel hatchery trout started to feed earlier, consumed more live prey, and lost less weight than when in allopatry. Hatchery trout grew more slowly than wild trout. To our knowledge, this is the first study to show that hatchery trout benefit from the presence of wild, experienced trout in a complex semi-natural environment. However, our results also indicate that the benefits to hatchery fish are not transferred to wild fish, and ultimately that care should be exercised in management actions when using hatchery trout to supplement wild populations. On the other hand survival potential of the novel hatchery brown trout could be better in the wild when also undomesticated trout are present.     

Size-dependent predator–prey relationships between pikeperch and their prey fish

Abstract –  Predator–prey interactions in aquatic food webs depend on the sizes of both predator and prey. In the present study, size-dependent interactions between >70 mm total length pikeperch Sander lucioperca (L.) and four different prey species in the biomanipulated Bautzen Reservoir were investigated. Gape widths of 597 pikeperch were measured, and the stomach contents of 806 specimens were analysed. Additionally, total lengths (TL) and body depths of 1448 prey fish were determined. The highest prey length to predator length ratio (PPR) was 0.63. Total lengths of piscivorous pikeperch and total lengths of prey fish [pikeperch, ruffe Gymnocephalus cernuus (L.) and roach Rutilus rutilus (L.)] were positively and linearly related. This was not the case for prey perch ( Perca fluviatilis L.) as all size groups of pikeperch fed strongly on age-0 perch. This study coupled with results of previous studies suggests that predation by pikeperch can have a major impact on the population dynamics of especially perch.     

Hooking mortality of white crappie, Pomoxis annularis Rafinesque, and spotted bass, Micropterus punctulatus (Rafinesque), in Texas reservoirs

Abstract. This study was conducted to estimate spring hooking mortality of white crappie, Pomoxis annularis Rafinesque, in Buchanan Reservoir, Texas, USA and summer hooking mortality of spotted bass, Micropterus punctulatus (Rafinesque), in Eagle Mountain Reservoir, Texas, USA. Reservoir surface water temperatures averaged 19 and 31°C, during white crappie and spotted bass experiments, respectively. White crappie (mean total length (TL) 267mm, range TL 190–340mm, standard error (SE) TL 6mm) were caught with size 5 single hooks baited with golden shiner, Notemigonus crysoleucas (Mitchill), and spotted bass (mean TL 220mm, range TL 143–326mm, SE TL 7mm) were caught with artificial lures (spinners) fitted with size 4 or 5 treble hooks. Fish were held in cages for 72 h to observe delayed mortality. Four of 43 white crappie (9·3%, 95% one-tail, upper confidence limit (UCL) = 13·7%) died and four of 47 spotted bass (8·5%, UCL = 15·2%) died. One of the white crappie that died was a sublegal-length fish. The relevance of these findings to the management of white crappie and spotted bass sport fisheries is discussed. It is concluded that under any management strategy necessitating release of some portion of the catch of white crappie and spotted bass, high survival of that portion could be expected.     

The effects of water depth on prey detection and capture by juvenile coho salmon and steelhead

Abstract –  We used three-dimensional video analysis of feeding experiments to determine the effects of water depth on prey detection and capture by drift-feeding juvenile coho salmon ( Oncorhynchus kisutch ) and steelhead ( O. mykiss irideus ). Depth treatments were 0.15, 0.30, 0.45 and 0.60 m. Mean prey capture probabilities for both species were constant across all treatments (coho = 0.51, steelhead = 0.39), and did not differ significantly between species. In deeper treatments, capture probabilities were lower nearer the surface than they were nearer the substrate, particularly at the lateral edges of the foraging area. In deeper treatments coho had greater capture probabilities nearer the surface than did steelhead. It is unclear if this was a species difference, or one based on the relative amount of foraging experience the fish had in the wild prior to capture. Prey capture manoeuver characteristics were very similar for both species, including positive relationships between water depth and both prey detection distance and prey interception swimming speed, and no relationship between depth and speed of return to the focal point. Because prey encounter rate is expected to increase with increasing water depth, we used capture probabilities to predict capture rates for coho and steelhead, which increased linearly with water depth. We conclude that any benefit of foraging in deeper water is more likely due to increased encounter rate rather than to increased capture probability.     

Growth of 0+ perch (Perca fluviatilis) predating on 0+ bream (Abramis brama)

Abstract – Larvae and juveniles of perch Perca fluviatilis and bream Abramis brama of Lake Speldrop, a highly eutrophicated gravel-pit lake in the floodplain of the Lower Rhine, were used in laboratory experiments to study predation of perch on bream. In the first series of experiments (control), 0+ perch of 30 mm total length (TL) did not prey on 0+ roach of about 24 mm TL. The perch fed only on zooplankton, resulting in low growth rates of 0.17 mm  ·  day⁻¹. In the second series of experiments, perch (30 mm TL) were combined with 0+ bream with an average TL of 14 and 19 mm at different ratios. As in the first series, even a nine-fold higher amount of zooplankton food had no significant influence on the growth rate of perch, regardless of the perch:bream ratio. At a perch: bream ratio of 7:1 and 4:4 all bream were eaten by the perch and restocked twice daily. At the end of the experiment, the TL of perch at a perch:bream ratio of 7:1 was significantly lower compared to a perch:bream ratio of 4:4 (mean growth rates at 7:1 of 0.16 mm  ·  day⁻¹ and at 4:4 of 0.35 mm  ·  day⁻¹). At the perch:bream ratio of 1:7, perch fed on bream in varying amounts, averaging between 3 and 12 bream per day and per individual. After 20 days, the final length of these fish was always significantly higher than the TL of perch at other perch:bream ratios and increased in correlation to number of bream eaten per day (mean growth rate 1.13 mm  ·  day⁻¹). The results are discussed with respect to the piscivore-dominated fish community of the eutrophied Lake Speldrop. ^Note     

Ecological significances of ontogenetic shifts in the stream-dwelling catfish, Hatcheria macraei (Siluriformes, Trichomycteridae), in a Patagonian river

Abstract –  The relationship between ontogenetic changes and both feeding and habitat preferences was studied in a stream catfish population of Argentine Patagonia. Fish capture, as well as habitat data recording, was performed during a 1-year long period. Larvae–juvenile transition was determined between 22.4 and 29.4 mm standard length (SL), on the basis of the relative growth changes and morphogenesis, and juvenile–adult shift was established between 61 and 65 mm SL using a macroscopic criterion of gonadal development and gonadosomatic index. Spawning period was estimated to be in the summer season, from December to February. Larvae preferred shallow marginal pools and fed mainly on small Chironomidae larvae, while juveniles and adults inhabited riffles and preyed on Ephemeroptera nymphs and Chironomid larvae. Morphological constraints during the larval period were related to habitat and feeding preferences. A complete development of fins allowed juveniles to colonise faster water habitats while a bigger mouth gape permitted them to prey on new items and on a larger size prey range.     

Comparison of visual acuity and visual axis of three flatfish species with different ecotypes

ABSTRACT:   The visual acuity, visual axis and visual accommodation of pointhead flounder, slime flounder, and red halibut were determined to obtain basic knowledge for developing appropriate fishing gear and fishing methods for sustainable fisheries. Each of these species has a different ecotype in terms of habitat, depth and prey species. Thus, it was hypothesized that they may differ in terms of visual acuity, visual axis and visual accommodation. Few studies have compared these characters in flatfishes from different ecotypes. We used histological methods to determine visual acuity (i.e. cone cell density) and visual axis (i.e. cone cell distribution) in each of these species. The maximum visual acuity was 0.127 in pointhead flounder (total length, TL 344 mm), 0.092 in slime flounder (TL 372 mm) and 0.109 in red halibut (TL 336 mm). Based on the cone cell distribution in the retina, the visual axis was upward and forward in pointhead flounder, forward and downward in slime flounder, and downward in red halibut. Finally, the mean angle of lens movement was −2° in pointhead flounder, −13° in slime flounder and −32° in red halibut. This measurement of lens movement indicated that the average near-point distance was 0.87 × TL in pointhead flounder, 0.65 × TL in slime flounder and 1.02 × TL in red halibut. At similar TL (336–355 mm), the visual acuity of these species differs depending on the direction in which they are looking.     

Cranial osteological development and abnormalities in northern palm ruff,Seriolella violacea (Guichenot, 1848), larvae and juveniles

Seriolella violacea, a new species to be potentially farmed in Chile and Peru, has shown cranial malformations during farming that could adversely affect its commercial development. This study seeks to generate early knowledge of the osteological development and type of cranial abnormalities that this species presents under culture conditions. Larvae from wild caught broodstock were reared from 1 to 60 days post hatching (DPH) (4.8 ± 0.1 mm TL and 11.8 ± 1.0 mm TL respectively). Larvae samples were collected throughout the experimental trial for recording cranial osteological development and abnormalities in cartilage and bone. At 5.7 ± 0.1 mm TL, coraco‐scapular, sclerotic, ethmoid plate and quadrate cartilages were present. At 8.0 ± 0.6 mm TL, early ossification was observed in the jaw, premaxilla and maxilla. At 11.8 ± 1.0 mm TL, the branchiostegal rays, jaw, maxilla and opercular complex were ossified. The first cartilaginous structures observed were the Meckel's cartilage, the branchial arches and the suspensory ligament. The first cranial malformations were detected at 5.7 ± 0.1 mm TL, coinciding with mouth opening. The most frequent malformations were a curvature of the lower jaw (23.1%), abnormal separation between branchial arches and the Meckel's cartilage (19.4%) and bulging jaws (15.7%).     

Diet composition of largemouth black bass, Micropterus salmoides (Lacepède), in southern Portuguese reservoirs: its relation to habitat characteristics

Abstract  During the summer of 1990 the diet of Micropterus salmoides (Lacepède) was studied in four southern Portuguese reservoirs. The dominant food items were insects (especially Odonata and Ephemeroptera naiads, and Odonata and Hemiptera adults), the crayfish, Procambarus clarkii (Girard), and pumpkinseed sunfish, Lepomis gibbosus (L.). There was an increase in the consumption of L. gibbosus as bass changed from 100–200 mm total length to over 200 mm, and a corresponding decline in the insect and crayfish components. Carp, Cyprinus carpio L., and other benthic cyprinids were absent from the stomach contents. The association between the different prey consumed and the habitat characteristics are discussed in relation to the feeding ecology of largemouth bass, an exotic species in Portugal.     

Differences in head shape of the European eel, Anguilla anguilla (L.)

Differences in eel, Anguilla anguilla (L.), head shape were the result of greater increases in head width, rather than changes in head length. The ratio of head width:total length (HW:TL) increased significantly ( t -test, P < 0.05) from the glass-yellow eel stage. Cultured yellow eels were exclusively narrow headed (mean HW:TL = 0.027, range = 0.023–0.032), while wild yellow eels displayed an array of head shapes (mean HW:TL = 0.033, range = 0.023–0.046). Therefore, broad heads (HW:TL 0.033) occurred only among wild yellow eels sampled and may have resulted from diet. Cultured yellow eels consumed only small pellet material. Of wild yellow eels stomachs containing food, 78% of broad-headed eels consumed large and/or hard-bodied organisms (e.g. beetles, fish, molluscs and Notonecta sp.), while 83% of narrow-headed eels consumed exclusively small/soft-bodied prey (e.g. amphipods and chironomids).     

Diet of introduced largemouth bass in Korean rivers and potential interactions with native fishes

Abstract –  A dietary analysis of largemouth bass ( Micropterus salmoides ), an exotic, piscivorous species, was conducted in large South Korean river systems (>third order streams, 31 sites). Micropterus salmoides larger than 100 mm exhibited intense piscivory on native Korean juvenile fishes, with levels of piscivory amongst the highest recorded globally, for native and introduced populations. Largemouth bass exhibited an ontogenetic shift in diet, showing a progressive increase in piscivory with size, typical of this species within its native range but unlike several studies on introduced largemouth bass in Europe and Africa. Sampling of fish communities at the same sites used for diet studies showed that native piscivores and the main food fish species of largemouth bass were significantly less abundant ( P  = 0.049 and 0.045, respectively) at sites where bass were present than at sites where no bass were recorded. Largemouth bass may pose a threat to the structure of fish assemblages in Korean river systems and further study of their population interactions and how to minimise their spread is needed.     

Food and feeding habits of ribbonfish Trichiurus lepturus in coastal waters of south-western Taiwan

ABSTRACT:   The catch of ribbonfish Trichiurus lepturus in the coastal waters of south-western Taiwan has significantly declined in recent years. To examine the effects of exploitation on the feeding habits of ribbonfish, 1570 specimens were collected on a monthly basis during March 2002–March 2003 from the landings by trawlers operating in the coastal waters of south-western Taiwan. The size of the ribbonfish ranged from 83–298 mm preanal length (PL), with a peak at 201–250 mm PL. Although they fed on shrimps and squid, fishes including Benthosema pterotum , Bregmaceros lanceolatus and Encrasicholina heteroloba were their main food items . In particular, B. pterotum was the most important food all year except during summer. No evidence of cannibalism was found in this study. No differences between day and night were found in the feeding activity of T. lepturus . However, B. pterotum and Acetes intermedius were the most important prey in the daytime, whereas B. lanceolatus , B. pterotum and E. heteroloba were at night. Feeding activity and the number of food items increased with increasing size of ribbonfish. Their feeding intensity in February to June, the main spawning season, was significantly greater than in other months. Changes in the food and feeding habits of this species before and after the recent period of heavy exploitation are discussed in detail in this study.     

Selective feeding in a generalist invertivore, age-0 striped bass

Abstract –  Age-0 striped bass ( Morone saxatilis ) and potential benthic and epibenthic invertebrate prey were collected at three sites in the mid-estuarine region of the Hudson River, New York, USA. Diet was related to prey availability to investigate the role of selectivity in feeding behaviour. The effects of prey availability and selectivity on stomach fullness were also examined. Gammarid amphipods and chironomid larvae were most numerous as stomach contents; and chironomid larvae, polychaetes, and isopods were the most numerous invertebrates captured. When selective feeding occurred, gammarid amphipods, Crangon spp. shrimp, and chironomid larvae were most commonly the preferred prey. Selective feeding correlated with higher stomach fullness. Fullness was also higher when the preferred prey was categorized as epibenthic versus benthic. Interaction between prey availability and environmental conditions appears to be an important determinant of age-0 striped bass feeding behaviour.     

Larval feeding behaviour of the endangered fish golden bubblebee goodeid, Allotoca dugesi, implications for conservation of an endangered species

Abstract To improve survival of cultured juvenile fishes, it is important to understand prey preferences and predation behaviour of fish larvae. In this study, the feeding behaviour and prey preference of Allotoca dugesi (Bean), a small fish species endemic to Mexico and currently threatened with extinction are presented. Three zooplanktonic prey, viz. Brachionus calyciflorus (Pallas) , Moina macrocopa (Goulden) and Daphnia pulex (Leydig) were tested. The mean size (standard length ± SE, mm) of the larvae ranged from 9.0 ± 0.1 mm at week 1 to 18 ± 2 mm at the end of the experimental period (8 weeks). The gape size (mean ± SE) increased from 0.125 ± 0.002 mm at the first week to 2.300 ± 0.361 mm by the eighth week. Capture success (capture/attack) ranged from 0.80 to 0.98 with Brachionus , 0.72–0.94 with Moina and 0.17–0.46 with Daphnia . Prey preference experiments were conducted using B. calyciflorus, M. macrocopa and D. pulex at a fixed ratio of 5 : 2 : 2 ind. mL⁻¹, respectively, and revealed a positive selection for rotifers and Moina , but avoidance of Daphnia . The results are discussed with reference to conservation efforts for Allotoca dugesi .     

Production and predation rates in a cannibalistic Arctic char (Salvelinus alpinus L.) population

Abstract – Production of cannibalistic Arctic char ( Salvelinus alpinus (L.)) and their prey conspecifics were estimated in an allopatric population, situated in an alpine ultraoligotrophic lake in central Norway. Estimates of population abundance were obtained by mark recapture and successive removal experiments. Assuming stable age distribution, we estimated mean yearly biomass (±95% CL) of char in sampled size groups vulnerable to predation (60 to 150 mm) to 7.93 (5.11–14.30) kg · ha⁻¹. Similarly, mean yearly biomass (±95% CL) of cannibalistic char (> 250 mm) was estimated to 0.62 (0.50–1.06) kg · ha⁻¹. Annual production (±95% CL) of char in length groups 60 to 150 mm was estimated to be 4.31 (2.74–8.03) kg · ha⁻¹ · year⁻¹, and production (±95% CL) of cannibalistic char to 0.19 (0.15–0.33) kg · ha⁻¹ · year⁻¹. Depending on the food conversion factor (set to vary from 0.1 to 0.4), the cannibalistic char removed from 10% to 40% of the production of char in sampled size-classes vulnerable to predation yearly. The overall ecological efficiency in energy transfer between the prey and predator population was 4.4%.     

Effects of Different Feed Habituation Methods on Survival and Feed Habituation Success of Largemouth Bass,Micropterus salmoides,in a Recirculating Aquaculture System

Demand for food size and trophy largemouth bass, Micropterus salmoides, is steadily increasing. However, largemouth bass, a carnivorous species, are more difficult to feed habituate than other commercially produced fish. Improving current feed habituation techniques to increase the percentage of fingerlings successfully feed habituated would increase profits, productivity and efficiency, and available product in the largemouth bass industry. The focus of this research was to evaluate different combinations of automatic feeders and supplemental hand feeding to determine the feed habituation success under commercial largemouth bass production conditions. Hand feeding, using only automatic feeders, or combinations of both, did not result in significant differences with regard to survival or feed habituation success. Initial fingerling size (total length, TL) was found to be the most important factor affecting survival and feed habituation success. Fish ranging from 40 to 50 mm (TL) survived and feed habituated at significantly higher rates than 30–40 and 50–60 mm (TL) fingerlings. Medium‐sized fish provide the best results in terms of feed habituation success and survival. The results suggest any combination of hand feeding and automatic feeders may be used to achieve feed habituating success in largemouth bass.     

Wild origin and enriched environment promote foraging rate and learning to forage on natural prey of captive reared Atlantic salmon parr

Abstract – After release to the wild, captive reared salmon have shown lower foraging rates on natural prey and impaired ability to avoid natural predators and thus lower survival compared with wild‐born conspecifics. Here, we examine whether captive breeding influences learning of foraging on natural prey and how enriched rearing methods may improve foraging on natural prey by Atlantic salmon (Salmo salar) parr. We reared offspring of hatchery or wild salmon of the same population in either a standard or enriched environment at production‐scale densities. The enriched environment featured submerged overhead shelter, varying water current, depth and direction and consequently alterations in food dispersion. Parr reared in the enriched environment expressed higher feeding rates, and parr of wild origin started to forage earlier on natural prey. The enriched method promoted foraging of hatchery reared parr on natural prey and is easily applicable to commercial production of salmonids for reintroduction or stock enhancement purposes.