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In degraded coral reef ecosystems, allelopathic macroalgae have received increasing attention from marine ecologists because their secondary metabolites (also known as allelochemicals) kill corals that grow adjacent to them and weaken the recovery of degraded reefs. One well‐known coral‐killing macroalga is the calcareous red seaweed Galaxaura. However, our knowledge of how coral reef fishes interact with allelopathic algae like Galaxaura is very limited. Here, we documented novel observations of feeding interactions of 17 species of coral reef fishes (herbivorous and carnivorous) with the filamentous Galaxaura divaricata on degraded lagoon patch reefs in Dongsha Atoll (South China Sea). Video analyses showed that territorial farming damselfishes (i.e., Dischistodus perspicillatus, D. prosopotaenia, Hemiglyphidodon plagiometopon, Pomacentrus grammorhynchus, P. adelus, and Neoglyphidodon nigroris) and juvenile parrotfishes (Scarus schlegeli, S. ghobban, S. rivulatus, and Chlorurus spilurus) likely used G. divaricata as a feeding substratum. Further, microscopic analyses revealed that the filamentous surface of G. divaricata harbored a wealth of epiphytic microalgae, such as filamentous cyanobacteria (i.e., Leptolyngbya, Lyngbya, Rivularia, Oscillatoria, and Stigonema), diatoms (i.e., Synedra, Nitzschia, Mastogloia, and Pleurosigma), and filamentous red algae (i.e., Heterosiphonia), suggesting that these fishes targeted the nutrient‐rich microscopic epiphytes rather than the nutrient‐poor host. Juvenile benthic carnivores (i.e., Labridae, Parupeneus multifasciatus, and Meiacanthus grammistes) form feeding assemblages with roving parrotfishes to feed on small invertebrates (i.e., amphipods, copepods, isopods, gastropods, and polychaetes) associated with G. divaricata. Given that coral reef fishes appear to target the epiphytes associated with Galaxaura rather than the alga itself, these observations thus substantiate the threat posed by the overgrowth of G. divaricata to coral recovery in degraded reef systems due to the lack of natural grazers. Chemical‐rich allelopathic macroalgae are competing with corals in sub‐/tropical reef ecosystems. According to the prevailing view, these algae deter herbivores with their secondary metabolites. Contrary to this view we observed that allelopathic macroalgae like Galaxaura divaricata  can provide a substratum for nutrient‐rich epiphytes that in turn present a food source for coral reef fishes. These observations suggest that Galaxaura may play an ecological role that has been overlooked and deserves our attention in the context of the resilience of coral reef ecosystems.

Environmental pollution by pharmaceuticals is increasingly recognized as a major threat to aquatic ecosystems worldwide. A variety of pharmaceuticals enter waterways by way of treated wastewater effluents and remain biochemically active in aquatic systems. Several ecotoxicological studies have been done, but generally, little is known about the ecological effects of pharmaceuticals. Here we show that a benzodiazepine anxiolytic drug (oxazepam) alters behavior and feeding rate of wild European perch (Perca fluviatilis) at concentrations encountered in effluent-influenced surface waters. Individuals exposed to water with dilute drug concentrations (1.8 micrograms liter -1 ) exhibited increased activity, reduced sociality, and higher feeding rate. As such, our results show that anxiolytic drugs in surface waters alter animal behaviors that are known to have ecological and evolutionary consequences.

The oligotrophic open ocean of low latitudes is larval fish habitat for a diversity of resident and migratory species. It is hypothesized that these waters, relative to coastal regions, yield reduced predation mortality, but little is known regarding the feeding and feeding environment of these larvae and the extent to which a nutritional tradeoff may exist, whereby lower predation mortality is accompanied by poor feeding conditions. Monthly sampling of larval billfishes (Istiophoridae) across the Straits of Florida over 2 yr allowed for an investigation of the temporal, spatial and ontogenetic variability in the feeding of sailfishIstiophorus platypterusand blue marlinMakaira nigricans. Consumed prey were numerically dominated (90%) by 2 crustaceans: a copepod (Farranula; mainlyF. gracilis) and a cladoceran (Evadne; mainlyE. tergestina), with relative proportions displaying marked spatial variability. These prey were consumed throughout early larval ontogeny, from first feeding through piscivorous lengths (>5 mm), until piscivory became exclusive near 12 mm. High daytime feeding incidence (0.94) and rapid digestion (~3.5 h) support generally frequent and successful feeding by billfish larvae. Prey selectivity was illustrated by preference forEvadneoverFarranulaand a near absence of calanoid copepods from diets despite high environmental concentrations. Gut fullness exhibited a distinct sunset peak and also differed significantly with larval length and year, but not with season or location. A gut evacuation rate was used to estimate a daily ration of 29 to 75% of gut-free body weight, varying greatly with model selection but also with daylight length. Although potentially unique to the Straits of Florida and larval billfishes, these results contradict the general presumption that the subtropical open ocean is nutritionally constraining for larval fish.

This book addresses current information on the effects of micronutrients and other efficacious substances from plants, animals and bacteria, with regard to quality and health of cultured fish. Each chapter contains tables, figures and is packed with many new references to help expand your knowledge of various aspects of fish culture technology. With fisheries scientists and students in mind, this book serves as a useful manual for your field of research.

Aquaculture's pressure on forage fisheries remains hotly contested. This article reviews trends in fishmeal and fish oil use in industrial aquafeeds, showing reduced inclusion rates but greater total use associated with increased aquaculture production and demand for fish high in long-chain omega-3 oils. The ratio of wild fisheries inputs to farmed fish output has fallen to 0.63 for the aquaculture sector as a whole but remains as high as 5.0 for Atlantic salmon. Various plant- and animal-based alternatives are now used or available for industrial aquafeeds, depending on relative prices and consumer acceptance, and the outlook for single-cell organisms to replace fish oil is promising. With appropriate economic and regulatory incentives, the transition toward alternative feedstuffs could accelerate, paving the way for a consensus that aquaculture is aiding the ocean, not depleting it.

Classical models of phytoplankton-zooplankton interaction show that with nutrient enrichment such systems may abruptly shift from limit cycles to stable phytoplankton domination due to zooplankton predation by planktivorous fish. Such models assume that planktivorous fish eat only zooplankton, but there are various species of filter-feeding fish that may also feed on phytoplankton. Here, we extend these classical models to systematically explore the effects of omnivory by planktivorous fish. Our analysis indicates that if fish forage on phytoplankton in addition to zooplankton, the alternative attractors predicted by the classical models disappear for all realistic parameter settings, even if omnivorous fish have a strong preference for zooplankton. Our model also shows that the level of fish biomass above which zooplankton collapse should be higher when fish are omnivorous than when fish are zooplanktivorous. We also used the model to explore the potential effects of the now increasingly common practice of stocking lakes with filter-feeding fish to control cyanobacteria. Because omnivorous filter-feeding fish forage on phytoplankton as well as on the main grazers of phytoplankton, the net effect of such fish on the phytoplankton biomass is not obvious. Our model suggests that there may be a unimodal relationship between the biomass of omnivorous filter-feeding fish and the biomass of phytoplankton. This implies that to manage for reductions in phytoplankton biomass, heavy stocking or strong reduction of such fish is best.

Fish feeding habit determines the digestive tract structure and intestinal microflora. However, the relationship between feeding habit, digestive intestinal morphology, and microbial diversity of omnivorous, herbivorous, plankton feeder, and carnivorous fish from the same environment has not been compared. This study compared the digestive enzyme activities, intestinal morphology, and intestinal microflora of omnivorous (Carassius auratus), herbivorous (Ctenopharyngodon idellus), carnivorous (Siniperca chuatsi), and plankton feeder (Schizothorax grahami) fishes and predicted the potential functions of specific microflora on different nutrients. Twelve intestine samples were collected from each of the four fishes from Dianchi Lake. The composition and diversity of microbial communities were determined by using high‐throughput sequencing of 16S rDNA. The results showed that the carnivorous fish (S. chuatsi) had higher trypsin and pancrelipase activities in the hepatopancreas and enteropeptidase in the intestine, but lower amylase activities in the intestine. The carnivorous fish intestine had more microvilli branches and complex structures than other fish species in the order carnivorous > herbivorous > plankton feeder > omnivorous. The intestinal microflora diversity was higher in the omnivorous fish and followed the order omnivorous > herbivorous > plankton feeder > carnivorous. Acinetobacter species and Bacteroides species were the most dominant flora in the carnivorous and herbivorous fishes, respectively. Acinetobacter species and Pseudomonas species might help the host to digest protein, while Bacteroidetes species may help the host to digest cellulose. Taken together, feeding habit determines the digestive enzyme activities, intestinal tissue morphology, and differential colonization of fish intestinal flora. The knowledge obtained is useful in feed formulation and feeding practices for the studied fish species. Feeding habit determines the digestive tract structure and intestinal microflora. However, the relationship between feeding habit, digestive physiology intestinal, and microbial diversity of omnivorous, herbivorous, filter‐feeder, and carnivorous fish reared in the same pond has not been compared. This study compared the digestive enzyme activities, intestinal morphology, and intestinal microflora of omnivorous (Carassius auratus), herbivorous (Ctenopharyngodon idellus), carnivorous (Siniperca chuatsi), and filter‐feeder (Shizothorax grahami) and predicted the potential functions of specific microflora on different nutrients.

The importance of copepods in aquaculture has long been recognized, especially in the larval rearing of many marine fishes. This timely publication provides a single source of information on copepod biology, culture methods and practical use in marine finfish hatcheries. Originating out of a workshop held on copepods by the Oceanic Institute in Hawaii, this proceedings includes review articles and papers presented by leading international experts in copepod biology and aquaculture. It is a seminal work that integrates the most up-to-date information on selecting copepod species, effects of algal species on reproduction, ways to increase production, the nutritional value of copepods, behavioral characteristics of copepods, potential use of copepod nauplii and eggs, and their application to larval rearing of various marine finfish species.

This paper reviews current knowledge on two feedstuffs, that is, insect meal and fish by-products, as alternatives to conventional animal protein sources. After an introductory part that highlights the need for sustainable development of animal production, the alternative protein sources are discussed. In particular, after providing some indications on their production and supply focussing on EU, a SWOT (Strengths, Weaknesses, Opportunities, and Threats) analysis was performed to identify the key factors that could help or impair the development of both protein sources production sectors. Finally, future perspectives are presented. The use of processed animal proteins derived from insects in farmed fish feeding is recognised by the EU legislation that authorises the use of proteins from seven insect species and the allowed substrates to rear insects. Insects have several advantages in nutritional value and the amino acid composition of their proteins generally meet animal requirements for good growth and health. The SWOT analysis indicated that insect meals can be considered as feed functional ingredients with beneficial properties that depend on the insect species, rearing system adopted, and the substrate used for their growth. Insects are expected to be increasingly used as a replacement for conventional animal-derived proteins, especially in aquafeeds. In the section regarding fishery and aquaculture by-products, the potential use of raw materials obtained during seafood processing is discussed. Peptides and amino acids recovered from as hydrolysed proteins can be used in animal feeds to partially substitute conventional protein feedstuffs thus providing nutrients, bioactive compounds and feed additives for animals. The SWOT analysis identified opportunities and weaknesses. Both the alternative protein sources are promising alternative feed ingredients for livestock production. Highlights The sustainable development of animal production sector needs alternative protein sources for feeds formulation. Insects and fishery- and aquaculture by-products represent optimal alternative protein sources. A SWOT analysis has identified the key factors for the development of both protein sources production sectors.

The oceanic convergence zone in the North Pacific Subtropical Gyre acts to accumulate floating marine debris, including plastic fragments of various sizes. Little is known about the ecological consequences of pelagic plastic accumulation. During the 2009 Scripps Environmental Accumulation of Plastics Expedition (SEAPLEX), we investigated whether mesopelagic fishes ingest plastic debris. A total of 141 fishes from 27 species were dissected to examine whether their stomach contents contained plastic particles. The incidence of plastic in fish stomachs was 9.2%. Net feeding bias was evaluated and judged to be minimal for our methods. The ingestion rate of plastic debris by mesopelagic fishes in the North Pacific is estimated to be from 12 000 to 24 000 tons yr–1. Similar rates of plastic ingestion by mesopelagic fishes may occur in other subtropical gyres.