Foraging strategy of the mudskipper Periophthalmus sobrinus Eggert in a Kenyan mangrove

The feeding behaviour of Periophthalmus sobrinus was studied in a population living along the channels of the Tana river delta. In November 1993 mudskippers were sampled every 2 tidal h for two consecutive spring and neap tides both during the day and night. The fishes were sexed and their stomach contents analysed. The results indicated that the mudskipper has a carnivorous diet and forages during both day and night although feeding greatly decreases after dark. Quantitative and qualitative differences in diet were found during the day and night of the two synodic and tidal phases. These differences were also demonstrable in the two sexes. The study showed that females of P. sobrinus are more selective than males and that differences between the two sexes may be related to reproductive condition. Furthermore, the mudskippers showed a tidal rhythm in feeding behaviour with peaks of activity around low tide (LT) on spring tides and around high tide (HT) on neap tides. Foraging activity seems to be influenced by the different spatial and temporal distributions of the mudskipper's prey caused by synodic, tidal and diel changes in the environment.     

Diel feeding rhythms and daily food consumption of juvenile Atlantic salmon in the River Alta, northern Norway

Atlantic salmon fry (0+) sampled from the River Alta exhibited only minor differences in stomach content weights and feeding rates throughout diel periods, but feeding rates were generally lowest at night. In contrast, salmon parr (1+ to 3+) had large diel fluctuations in stomach content weight, with the largest weights usually being recorded during the night and early morning. Accordingly, their feeding rates were highest at night. This nocturnal feeding pattern was consistent throughout all sampling occasions, and appeared to reflect a persistent feeding periodicity in the salmon parr. The daily food consumption rates of both fry and parr were highest during midsummer and decreased towards autumn.     

Fluorescence analysis of zooplankton gut contents and an investigation of diel feeding patterns

A method is described for measurement of the in situ feeding rate of planktonic herbivores. Freshly caught Zooplankton are washed with filtered sea water and frozen. The gut contents are later analysed using acetone extracts of the entire sample. Fluorescence peaks due to ingested chlorophyll are easy to quantify for sample sizes of 20–200 animals. This method obviates some of the problems, such as confinement and previous feeding history, associated with extrapolation from laboratory experiments to field conditions. The method is illustrated by an investigation of diel feeding patterns of marine copepods. Initial results indicate the complexity of these patterns, with either a single night peak or dawn and dusk peaks for adult copepods. Diel variations in feeding activity appear to occur in addition to, but closely interacting with, the diel vertical migrations of the animals.     

Diel shifts in the structure and function of nearshore estuarine fish communities

Day–night shifts in the nearshore fish fauna of a temperate microtidal estuary were assessed using a holistic suite of structural and functional community attributes. Mean fish species richness and diversity (taxonomic distinctness) were higher at night across all regions of the estuary and seasons, concurring with the findings of numerous comparable studies reviewed worldwide, while the diel period in which mean abundance was higher varied among seasons. Likewise, species and functional guild compositions (the latter based on feeding modes and habitat use) both differed significantly between day and night, with the extent of the diel shift again varying seasonally. Daytime fish communities were characterized by higher abundances of Atherinidae, Sillaginidae and Mugilidae, while Gobiidae were far more abundant at night. Marked shifts in size composition were also evident, with smaller fishes (<100 mm total length, L_T) being more prevalent during the day and larger fishes (≥200 mm L_T) proportionally more abundant at night. The above diel shifts were feasibly related to a range of predator–prey interactions and feeding‐related movements, namely a nocturnal decrease in top‐order avian piscivory coupled with an increase in invertebrate prey availability, resulting in changes in the presence and catchability of certain fish species in shallow estuarine waters.     

Diel vertical migration and feeding rhythm of Daphnia longispina and Bosmina corexoni in Lake Toya, Hokkaido, Japan

Diel vertical migration (DVM) and diel feeding rhythm of two cladocerans, Daphnia longispina and Bosmina coregoni were investigated at the pelagic area of Lake Toya (Hokkaido, Japan) in May, August and October 1992. Both species performed nocturnal DVM. The amplitude of DVM, however, became smaller from May to October. Such seasonal variations in DVM could not be explained by light penetration and/or water temperature. The two species had a clear feeding rhythm; they fed at night in May and October but also after sunrise in August. These feeding rhythms appeared to be related to the light-dark cycle, but were not necessarily associated with their DVM. We suggest that the diel feeding rhythm and DVM are regulated independently by light cues.     

The food of brown and rainbow trout (Salmo trutta and S. gairdneri) in relation to the abundance of drifting invertebrates in a mountain stream

Summary The diet of Salmo gairdneri and S. trutta in a Pyrenean stream was very similar, and was also similar to the percentage composition of the drift but not the benthos. There was a good correlation between diel changes in the amount of food (both numbers and biomass) in the stomachs and diel changes in the abundance of drifting invertebrates. The major feeding period was in the early hours of the night when the trout fed chiefly on benthic invertebrates in the drift. This was the only feeding period in experiments 1 and 2 (mean water temperatures 4.7 and 7.3° C) but in experiment 3 (10.8° C), there was a second feeding period in the day when terrestrial invertebrates and emerging aquatic insects formed a large proportion of the diet.Neither species was consuming a greater amount of food than the other. The weight of food consumed/trout/day increased with water temperature, and was close to the daily food requirements for resting metabolism in experiment 1. for twice resting metabolism (active metabolism) in experiment 2, and for four times resting metabolism in experiment 3. Therefore the energy of the second meal in experiment 3 was available for growth.The effect of temperature, on rates of gastric evacuation was the chief factor which determined the number of meals/day; the availability of food organisms in the drift determined the time of feeding; and the requirements for metabolism (affected by temperature and body weight) determined the amount of energy left for growth.     

Short communication. Food availability and diel feeding rhythms in the marine copepods Acartia grani and Centropages typicus

The effects of food availability on the daily feeding pattern of planktonic copepods was studied for two species: Acartia grani (cultured and wild specimens) and Centropages typicus (wild specimens). Both species showed clear diel feeding rhythms at high food concentrations, with significantly higher clearance rates during night hours. However, at limiting food conditions, while C.typicus maintained its daily feeding pattern, A.grani fed continuously, with similar day and night clearance rates. These results could be explained in relation to differences in predation risks and probability of experiencing starvation episodes in their respective habitats, as well as their capacity for dampening food fluctuations. On the other hand, the maintenance (although with less intensity) of the diel feeding rhythm in A.grani, when cultured in the laboratory for long periods of time (>10 generations) and in the absence of predators, suggests the importance of the endogenous control of copepod feeding patterns.      

Temporal Links in Daily Activity Patterns between Coral Reef Predators and Their Prey

Few studies have documented the activity patterns of both predators and their common prey over 24 h diel cycles. This study documents the temporal periodicity of two common resident predators of juvenile reef fishes, Cephalopholis cyanostigma (rockcod) and Pseudochromis fuscus (dottyback) and compares these to the activity and foraging pattern of a common prey species, juvenile Pomacentrus moluccensis (lemon damselfish). Detailed observations of activity in the field and using 24 h infrared video in the laboratory revealed that the two predators had very different activity patterns. C. cyanostigma was active over the whole 24 h period, with a peak in feeding strikes at dusk and increased activity at both dawn and dusk, while P. fuscus was not active at night and had its highest strike rates at midday. The activity and foraging pattern of P. moluccensis directly opposes that of C. cyanostigma with individuals reducing strike rate and intraspecific aggression at both dawn and dusk, and reducing distance from shelter and boldness at dusk only. Juveniles examined were just outside the size-selection window of P. fuscus. We suggest that the relatively predictable diel behaviour of coral reef predators results from physiological factors such as visual sensory abilities, circadian rhythmicity, variation in hunting profitability, and predation risk at different times of the day. Our study suggests that the diel periodicity of P. moluccensis behaviour may represent a response to increased predation risk at times when both the ability to efficiently capture food and visually detect predators is reduced.     

Diel variations in the assemblage structure and foraging ecology of larval and 0+ year juvenile fishes in a man‐made floodplain waterbody

This study investigated diel variations in zooplankton composition and abundance, and the species composition, density, size structure, feeding activity, diet composition and prey selection of larval and 0+ year juvenile fishes in the littoral of a man‐made floodplain waterbody over five 24 h periods within a 57 day period. There was a significant difference in the species composition of diurnal and nocturnal catches, with most species consistently peaking in abundance either during daylight or at night, reflecting their main activity period. There were no consistent diel patterns in assemblage structure or the abundance of some species, however, most likely, respectively, due to the phenology of fish hatching and ontogenetic shifts in diel behaviour or habitat use. There were few clear diel patterns in the diet composition or prey selection of larval and 0+ year juvenile roach Rutilus rutilus and perch Perca fluviatilis, with most taxa consistently selected or avoided irrespective of the time of day or night, and no obvious shift between planktonic and benthic food sources, but dietary overlap suggested that interspecific interactions were probably strongest at night. It is essential that sampling programmes account for the diel ecology of the target species, as diurnal surveys alone could produce inaccurate assessments of resource use. The relative lack of consistent diel patterns in this study suggests that multiple 24 h surveys are required in late spring and early summer to provide accurate assessments of 0+ year fish assemblage structure and foraging ecology.     

Nocturnal hatching timing of mouthbrooding male cardinalfish Apogon niger

We observed hatching behavior by mouthbrooding males of the cardinalfish, Apogon niger. Mouthbrooding males showed no feeding activities at night, in spite of their nocturnal feeding habit. On the day of hatching, they released newly hatched larvae from their mouths on average 81 min after sunset. Semilunar hatching periodicity was significant, but its diel pattern was independent of the tidal rhythm. Sunset hatching may be advantageous not only to offspring because of their low predation risk but also to parental males because they can resume feeding sooner, thereby reducing the energetic loss from fasting while mouthbrooding. Received: August 22, 2000 / Revised: November 28, 2000 / Accepted: January 12, 2001     

Ontogenetic shifts in drift periodicity and benthic dispersal in elmid beetles

1. There is a paucity of information on ontogenetic changes in the dispersal of benthic invertebrates, which is an important aspect of their ecology. This study quantifies ontogenetic changes in diel periodicity in drift, and in upstream–downstream dispersal on the substratum for Elmis aenea, Oulimnius tuberculatus, Esolus parallelepipedus and Limnius volkmari (Coleoptera: Elmidae). Three drift nets were emptied every 3 h over 24 h in each month (October 1965–December 1968) at two contrasting sites: one in a deep section with abundant macrophytes, the other in a shallow stony riffle. Comparisons of periodicity between life‐stages of the same species were limited to months when numbers in the drift were highest. Dispersal was evaluated in six experimental stream channels, placed above the stream, with initial numbers of each life‐stage varying from 20 to 80. 2. Drift numbers were always highest at night with few or no animals in the day samples. Ontogenetic shifts in diel periodicity were similar for all four species. Drift catches were similar throughout the night for the early and intermediate larval instars and for mature adults, but were highest in the early hours of the night with a gradual decline thereafter for later larval instars and immature adults. These patterns were unaffected by a severe spate, even though drift numbers increased considerably. 3. Dispersal was density‐independent; the number of dispersing animals was a constant proportion of the initial number for each life‐stage. The relationship between dispersal distance and the number of animals travelling that distance was well described by an inverse power function. Median and maximum distances (m day^?1) were estimated for each life‐stage. 4. Ontogenetic shifts in dispersal in the stream channels matched those shown in diel drift periodicity. For all four species, the later larval instars and immature adults showed little movement in either direction, whereas early and intermediate larval instars and mature adults dispersed predominantly upstream, adults travelling further than any other life‐stage. 5. Ontogenetic shifts in diel drift periodicity and dispersal were related to seasonal changes in drift density and critical periods in the life cycle. Such shifts have not been quantified in other stream invertebrates, but should be considered when evaluating the role of dispersal in their population dynamics and their colonization ability.     

马鞍列岛多种生境中鱼类群聚的昼夜变化

为了解岛礁水域鱼类群聚的昼夜变化特征,以便更全面地设计采样方法和掌握采样的时间尺度,于2009年9月对马鞍列岛7种生境进行了共计24网次的刺网昼夜采样,结合排序和聚类方法,从种类组成、相对生物量和丰度、种类丰富度、多样性和相似性等方面对研究海域鱼类群聚特征的昼夜变化作了探讨.在采获的55种鱼类中,昼夜出现的分别为41和46种,数量差别不大,但其昼夜组成却随栖息水层的变化而不同,底层鱼类更趋向于夜间在硬相生境集群活动;近底层鱼类的昼夜集群随生境变化而变化,在同一生境中既有偏向白天也有趋向夜间的;中上层鱼类更多地出现在白天的人工生境(AH).AH白天的丰度渔获率显著大于晚上,而天然生境(NH)昼夜差别不大;生物量渔获率无论NH还是AH皆无显著昼夜差异.具体到种类,仅有小黄鱼Larimichthys polyactis和赤鼻棱鳗Thryssa kammalensis等少数种类的数量在AH有显著的昼夜差别,其他多数种类虽然昼夜的出现率大多有别,但渔获率昼夜差异皆不明显.多样性差异更多的表现在不同生境之间,而同一生境的昼夜差异往往不甚显著.各个生境中鱼类的昼夜种类交替现象非常明显,形成了以褐菖(鲐)Sebastiscus marmoratus和鳗鲇Plotosus anguillaris为代表的夜间优势类群为主的硬相生境群聚格局、以丝背细鳞鲀Stephanolepis cirrhifer和细刺鱼Microcanthus strigatus为代表的白天优势类群为主的硬相生境群聚格局以及缺乏底层优势类群、以石首鱼科鱼类为代表的近底层鱼类为绝对优势类群的软相生境群聚格局.因此,采用被动性渔具在近岸典型生境进行鱼类等相关生物调查时,应使采样时间覆盖昼夜两个时段,且至少保证24h.     

Diel and density-related changes in food consumption and prey selection by brook charr in a New Hampshire stream

Synopsis We report the results of a field study testing influences of both density and changes over the diel cycle on food consumption and prey selection by brook charr,Salvelinus fontinalis. Charr density in replicate 35 m long sections of a New Hampshire stream was adjusted to either medium or high levels (relative to natural densities). Diets of charr and the availability of drifting prey were then sampled every four hours for 24 hours. There were no significant diel changes in the weight of prey consumed by charr per four hours, though there was some indication of reduced feeding at night. Chary fed selectively on different prey taxa, showing most preference for cased caddis larvae. Several species of mayflies and stoneflies were selected more strongly during the day than at night. Charr fed selectively on larger prey during the daytime but showed no size-selection at night. The density of charr had no significant effects on either their rate of food consumption or on selection for prey of different taxa or sizes.     

Influence des variations de la composition faunistique d'une population zooplanctonique sur l'expression des activités enzymatiques digestives au cours d'un cycle nycthéméral

Diel changes in the digestive enzyme activities of a Zooplankton population, captured with a Regent type net (700 μm mesh size) have been studied. During the period considered, the population was dominated by the appendicularian Oikopleura dioica Fol and several species of copepods. A clear rhythmicity was observed for most carbohydrases (laminarinase, amylase, cellulase, disaccharidases) but not for proteases. Changes in population composition explained a significant part of the enzymatic variability, although part of it still corresponded to nutritional rhythmicity. These results stress the importance of the physical and biological conditions of the environment when considering metabolic rhythmic changes at the population or the individual level.     

Diel variation in diet composition of a riverine fish community

Although diel food habit studies have been undertaken on a number of individual species, few studies have examined diel variation in the diets of fish communities. We examined the diel diet variation and feeding periodicity of a fish community in the Juniata River, Pennsylvania. Nine species, totalling 1,098 fish, were collected at 4-h intervals over a 24-h period in October 1989, in numbers sufficient to describe their diel variation in diet composition. Diel variation in diet composition was evident in all species, as no single prey taxon was dominant in the diet of any species during any 4-h interval. Ephemeropterans were the most important prey taxa for four species of centrarchids, whereas chironomids were the main prey of banded killifish, mimic shiners, and spotfin shiners. Algae was the major component in the diet of spottail shiners, whereas bluntnose minnows contained mostly detritus. Feeding activities of rock bass, redbreast sunfish, and pumpkinseed occurred at low levels throughout the day; peak feeding occurred from 2000 to 0400 hours. Food consumption of smallmouth bass increased throughout the day with peak consumption occurring at 2000 hours. Non-centrarchids fed little during daylight hours and showed peak activity at 2000–2400 h. Construction of a 24-hour diet from six 4-h interval estimates and feeding periodicity data provided a comprehensive representation of the diel feeding ecology of all species collected.     

Fish sampling in the marine-dominated Kariega Estuary,South Africa,using a demersal otter trawl: day/night effects

Very few demersal fish assemblage studies using otter trawls in estuaries have been done in South Africa and none of these have tested for the effects of diel period. This study aimed to test whether diel period affects otter trawl catches in the clear, permanently open Kariega Estuary in terms of both species composition and abundance. Fish were sampled by day and night from 30 October to 1 November 2007 at 15 sites using an otter trawl. More species were collected at night, when there were higher catch rates for all key species, with the exception of Rhabdosargus holubi, which was more abundant during the day. Overall assemblages collected by day and by night were similar, with six species accounting for over 90% of the catch in both day and night samples. Both day and night samples reflected differences related to region, with the highest mean CPUE during day and night sampling being recorded in the head region.     

Diel feeding patterns of the congiopodid fishHypodytes rubripinnis in Aburatsubo Bay,Japan

Diel changes in the feeding intensity and diet composition of the congiopodid fishHypodytes rubriphnnis were studied in Aburatsubo Bay, Miura Peninsula, Japan, on July 24 and 25, 1985. In samples taken at night, the ratio of stomach content weight to body weight was high and the frequency of occurrence of fish with empty stomach was very low, while the reverse was the case in the daytime, suggesting that this species feeds intensively at night, instead of during the day. Gammarids were the most dominant prey and isopods and caprellids were next important. These three prey items accounted for 91% of the total diet by number. The proportion of isopods in the total diet showed the most remarkable diel change. They amounted to about 30% at night, but were not consumed in the daytime.     

A comparative study on the regulation of C3 and C4 carboxylation processes in the constitutive crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana and the C3-CAM intermediate Clusia minor

A comparison of carbon metabolism in the constitutive crassulacean acid metabolism (CAM) plant Kalanchoë daigremontiana Hamet et Perr. and the C₃-CAM intermediate Clusia minor L. was undertaken under controlled environmental conditions where plants experience gradual changes in light intensity, temperature and humidity at the start and end of the photoperiod. The magnitude of CAM activity was manipulated by maintaining plants in ambient air or by enclosing leaves overnight in an atmosphere of N₂ to suppress C₄ carboxylation. Measurements of diel changes in carbonisotope discrimination and organic acid content were used to quantify the activities of C₃ and C₄ carboxylases in vivo and to indicate the extent to which the activities of phosphoenolpyruvate carboxylase (PEPCase), ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) and decarboxylation processes overlap at the start and end of the photoperiod. These measurements in vivo were compared with measurements in vitro of changes in the diel sensitivity of PEPCase to malate inhibition. The results demonstrate fundamental differences in the down-regulation of PEPCase during the day in the two species. While PEPCase is inactivated within the first 30 min of the photoperiod in K. daigremontiana, the enzyme is active for 4 h at the start and 3 h at the end of the photoperiod in C. minor. Enclosing leaves in N₂ overnight resulted in a two-to threefold increase in PEPCase-mediated CO₂ uptake during Phase II of CAM in both species. However, futile cycling of CO₂ between malate synthesis and decarboxylation does not occur during Phase II in either species. In terms of overall carbon balance, C₄ carboxylation accounted for ≈ 20% of net daytime assimilation in both species under control conditions, increasing to 30–34% after a night in N₂. Although N₂-treated leaves of K. daigremontiana took up 25% more CO₂ than control leaves during the day this was insufficient to compensate for the loss of CO₂ taken up by CAM the previous night. In contrast, in N₂-treated leaves of C. minor, the twofold increase in daytime PEPCase activity and the increase in net CO₂ uptake by Rubisco during Phase III compensated for the inhibition of C₄ carboxylation at night in terms of diel carbon balance.     

Diel vertical migration and gut pigment rhythm of Paracalanus parvus,P. crassirostris,Acartia erythraea and Eucalanus subcrassus (Copepoda,Calanoida) in Tolo Harbour,Hong Kong

Diel vertical migration and gut pigment rhythm of calanoid copepods were studied in the highly eutrophic waters of Tolo Harbour, Hong Kong in summer between July 30 and August l, 1991 and in winter between January 24 and 25, 1992. Paracalanus parvus and P. crassirostris showed neither diel vertical migration nor diel gut pigment rhythm during the summer study. Acartia erythraea and Eucalanus subcrassus exhibited prominent diel vertical migration and diel gut pigment rhythm. Diel changes in gut pigment content of surface dwelling individuals and increase of gut pigment content before the onset of nocturnal upward migration suggest that gut pigment rhythm in E. subcrassus was not the result of animals moving in and out of a food-rich surface layer. During the winter study, the harbour was affected by a bloom of Noctiluca scintillans. P. parvus and P. crassirostris resided in deeper waters presumably to avoid the dense populations of N. scintillans at the surface. P. crassirostris remained non-migratory during the winter study. There was a nocturnal increase in the number of P. parvus in the surface waters, although no diel change in the mean depth of the population was observed. Both Paracalanus species showed diel gut pigment rhythm. The presence of diel gut pigment rhythm in the non-migratory P. crassirostris during the winter study suggested the presence of an independent feeding rhythm.