Description: Food uptake follows rules defined by feeding behaviour that determines the kind and quantity of food ingested by fish larvae as well as how live prey and food particles are detected, captured and ingested. Feeding success depends on the progressive development of anatomical characteristics and physiological functions and on the availability of suitable food items throughout larval development. The fish larval stages present eco-morpho-physiological features very different from adults and differ from one species to another. The organoleptic properties, dimensions, detectability, movements characteristics and buoyancy of food items are all crucial features that should be considered, but is often ignored, in feeding regimes. Ontogenetic changes in digestive function lead to limitations in the ability to process certain feedstuffs. There is still a lack of knowledge about the digestion and absorption of various nutrients and about the ontogeny of basic physiological mechanisms in fish larvae, including how they are affected by genetic, dietary and environmental factors. The neural and hormonal regulation of the digestive process and of appetite is critical for optimizing digestion. These processes are still poorly described in fish larvae and attempts to develop optimal feeding regimes are often still on a ‘trial and error’ basis. A holistic understanding of feeding ecology and digestive functions is important for designing diets for fish larvae and the adaptation of rearing conditions to meet requirements for the best presentation of prey and microdiets, and their optimal ingestion, digestion and absorption. More research that targets gaps in our knowledge should advance larval rearing.

Description: The management of recreational fisheries benefits from good collaboration between scientists, managers and recreational fishers. However, the level of collaboration largely depends on the levels of effective communication among the different stakeholders. This paper presents the views of scientists, managers and fishers concerning the quality of communication in eleven case studies of recreational fisheries. Case studies were synthesised and common reasons why communication did not always flow as intended were identified. The prevalent barriers to good communication, and therefore collaboration included a lack of rigorous scientific information transfer from scientists to fishers and managers, a fear from fishers that management actions will limit fishing opportunities, pre-existing antagonism between commercial and recreational fisheries, and fishers' suspicion of science. Overcoming these issues is paramount to improve collaboration and participatory processes that help lead to robust, well-accepted management actions

Description: The early life-history of Chinese rock carp Procypris rabaudi was investigated during a 56-day rearing period: 318 artificially propagated P. rabaudi larvae were reared throughout metamorphosis in a small-scale recirculation system (345 L water volume, 10 × 18 L rearing tanks, 150 L storage and filter compartment with bioballs, 20–30 larvae L−1) at the Institute of Hydrobiology, Wuhan, Hubei Province, China. The newly hatched larvae had an initial total length of 8.93 ± 0.35 mm SD (n = 10) at 3 days post-hatch and reached an average total length of 33.29 mm (±1.88 mm SD, n = 10) 56 days after hatching. Length increment averaged 0.45 mm day−1, resulting in a mean growth of 24.4 mm within the 56-day period. High mortality rates of up to 92% derived from an introduced fungus infection and subsequent treatment stress with malachite green. Our results indicate that Chinese rock carp can be raised successfully from artificially fertilized eggs. We therefore assume this species to be a candidate for commercial aquaculture.

Description: The studies which form the background for this synoptic presentation aimed to contribute to the investigation of the reason for great yearly fluctuations in recruitment in marine fish stocks. In order to evaluate if mass mortality due to starvation in the larval stage contributes to these fluctuations, trypsin activity was suggested as an appropriate indicator to assess individually both the nutritional condition and feeding activity of fish larvae of all age stages. Based on the principle of conventional chromogenic methods a highly sensitive fluorometric measurement was developed, which allows the individual assessment of tryptic activity even in the youngest larval stages. In order to evaluate species-specific features of tryptic activity, larvae of six different marine species were reared under laboratory conditions (herring, Clupea harengus, turbot, Scophthalmus maximus, cod, Gadus morhua, sea bass, Dicentrarchus labrax, gilthead seabream, Sparus aurata, and Brazilian sardine, Sardinella brasiliensis). The exemplary application of the laboratory calibration in field surveys clearly demonstrates that the tryptic activity is appropriate to evaluate the nutritional condition of larvae from field samples. Examples for some species are presented (herring, cod and sprat). The most significant results from laboratory experiments: Larval age and larval size were chosen as the standard for comparison to relate to tryptic activity. Tryptic activity was found even in yolk sac stages of the investigated species. Tryptic activity increases with age in continuously fed larvae following a non-linear pattern which is supposed to be determined in the ontogenetic development of each species. Increase in tryptic activity persists until larvae develop a functional stomach. The amount of maximum tryptic activity at a given size and age is species specific: turbot larvae show the highest whereas herring larvae have the lowest values at a given age. The amount of trypsin which has its origin in the ingested food oganism is of minor significance for the measurement. Tryptic acticity reacts very sensitive on variations in food density. Not only fed and starved larvae can be separated but also larvae kept at high and low food concentration. Differences in tryptic activity between fed and starved larvae are statistically significant in the majority of the investigated species, but differences in larvae kept at high and low food densities are not always significant. In yolk sac stages and beyond, while adapting to exogenic food sources, differences in tryptic activity are insignificant in larvae with and without food supply. This stage can last until ten days after hatching, depending from the species. When relying completely on external food sources, differences in tryptic activity occurs within hours when fed and starving larvae are compared. However, significant differences arise only after 1- 3 days, depending on species, size and age. Species with their origin in temperate latitudes shows a slower decrease in tryptic activity compared to species from subtropical or tropical areas. If food deprivation persists, tryptic activity levels off to zero within days; the number of days is depending from the species, age and size. Individual variability of tryptic activity is large in continuously fed larvae, moderate in larvae kept on low food density and disappears in starving larvae. A diurnal rhythm in tryptic activity was identified. In addition, tryptic activity increases as a consequence of active feeding and decreases thereafter within hours to the pre-feeding level; however, those level is always well above the tryptic activity level of starving larvae. Starving larvae show a very weak diurnal oscillation in tryptic activity. 196 Laboratory calibration was used to estimate the number of starving larvae in field samples. For this purpose, tryptic activity was related to the larval size and the values for starving larvae were fitted to a linear regression. The upper 99% prediction limit of the regression analyses fitted to starving larvae was used as threshold value to assess the nutritional condition of field samples. Larval length was chosen as reference value for tryptic activity, since tryptic activity rather depends on the developmental stage (size) than on larval age; further it is easy to measure the length in larvae from field samples and moreover, the length is not much affected when larvae are in a bad condition (compared to larval weight or protein content). Ideally, the species from field surveys should have a calibration background under laboratory conditions; however the application of laboratory results appears to be valid within the same taxa (e.g. Clupeidae). An example is given in this presentation. Results from experiments with turbot larvae indicate that tryptic activity measurements can be used to optimize the food ration and the time of feeding in growing larvae in aquaculture. The exemplary application of the laboratory calibration in field surveys clearly demonstrates, the tryptic activity is appropriate to evaluate the nutritional condition of larvae from field samples. Examples for some species are presented (herring, cod and sprat). The most significant results from field studies: Nutritional condition of herring larvae from two different, but typical spawning locations (Hebrides-Orkney-Shetland in autumn season, English Channel in January) were evaluated and compared. Starving larvae in the range of 0-80% were found for the autumn spawners, however only small larvae around 10mm were concerned; about 27% of the larvae caught in the English Channel were rated as starving larvae, but larvae of all sizes were concerned. The results are in accordance with the usually expected environmental conditions in those areas (food availability and hydrographic conditions). In the context of a a large scale study on sprat recruitment (Sprattus sprattus) in the North Sea (SARP, Sardine-Anchovy-Recruitment-Program), a survey on the condition of sprat larvae throughout the whole spawning season was conducted (sprat are batch spawners). The tryptic activity of sprat larvae were assessed from May to August and compared to the abundance of juvenile sprat in the related area in autumn of the same year. There was a clear positive relation between the periods with larvae in a fair nutritional condition and the number of juvenile sprat and vice versa. Results on the abundance of food availability in the investigated area confirmed these observations. Nutritional condition of cod larvae from field samples from the Baltic were rated in accordance with the laboratory calibration. About 30% of starving larvae of all sizes were calculated. The results show, that not only the youngest larval stages are concerned from weak nutritional conditions. Investigations on the diurnal rhythm of tryptic activity in field samples of sardine larvae showed a clear periodical day and night pattern. Low tryptic activities were measured in samples from afternoon to dusk, whereas high activities were measured in samples from midnight to dawn. In accordance with related laboratory results it can be concluded, that feeding activity is responsible for the clear pattern. Concluding, the results suggest that mortality due to starvation is of significance in marine fish larvae.

Description: We reconstructed marine fisheries catches for the Federal Republic of Germany within the North Sea (specifically ICES area IVb) from 1950-2010. ICES landings statistics are used as a reported baseline, and then adjusted using information from ICES stock assessment working group reports, national data, and expert knowledge to estimate unreported landings, recreational and subsistence catches and major discards. Brown shrimp (Crangon crangon) contribute the most to unreported landings and discards. Atlantic herring (Clupea harengus), Atlantic cod (Gadus morhua) and European plaice (Pleuronectes platessa) are also important fisheries for the period 1950-2010. The reconstructed total catch of 8.5 million t from 1950-2010 was approximately 63% higher than the baseline reported ICES landings of 5.2 million t. The reconstructed total catch of invertebrates is almost 4 million t, which is 2 times the ICES baseline catch which is just over 1.9 million t. The reconstructed catch for all finfish species is 4.6 million t and is 41% higher than the ICES baseline catch of 3.3 million t. These discrepancies are largely driven by discarded catches that are not accounted for in officially reported (ICES) data, which also form the globally reported data as presented by the Food and Agriculture Organization of the United Nations. Our results demonstrate the importance of comprehensively accounting for and disclosing fisheries data to the public (including discarded catches), and effectively monitoring Illegal, Unreported and Unregulated (IUU) catches.

Description: In developmental studies of fish species (especially physostomians) it could be demonstrated, that the lack of haemoglobin during larval and juvenile stages is a relatively common phenomenon. Generally it is linked with body translucency. In representatives of the families Galaxiidae, Osmeridae and Clupeidae, partly reared, partly observed immediately after being caught in the wild, it turned out, that this condition coincides with a considerable delay in swimbladder inflation. To determine the moment of its first inflation, larvae placed in a hermetic chamber were observed under a dissecting microscope. While lowering the pressure, the expanding swimbladder showed whether or not its content is really gaseous. The reason postulated to be responsible for the delayed inflation is that larvae lacking haemoglobin do not have the possibility of oxygen transport to their buoyancy organ by means of the blood. Apart of this, capillarity force calculations and body force estimations show that with decreasing size the constraints linked with surface tension increase overproportionally. While in larger sized larvae like trout we could demonstrate inflation by swallowing air, in species with small larvae this was not the case. Below a certain size, even in physostomians, the ductus pneumaticus is no alternative to the blood pathway for swimbladder inflation.

Description: The aim of this study was to evaluate the potential of a compound diet as a live prey substitute for feeding European sea bass larvae (Dicentrarchus labrax L.). The effect of a commercial diet (Nippai ML feed) and live prey (Artemia nauplii) on tryptic enzyme activity, protein content, growth (standard length) and survival rates of sea bass larvae were tested during a 27-day rearing experiment. Sea bass larvae were divided into two groups. The live food group (control group) was fed exclusively on newly hatched Artemia nauplii (Inve AF grade), the test group was fed exclusively with the compound diet from day 15 onwards. As trypsin has been demonstrated to be a useful indicator for evaluating digestibility of food and the nutritional condition of fish larvae, individual tryptic enzyme activity was determined in both feeding groups. Larvae older than 14 days after hatching and fed on live food showed a significantly higher tryptic enzyme activity than larvae fed the compound diet. A similar relationship between tryptic activity and standard length in both test groups was detected only in small larvae (standard length 〈 7 mm). The usefulness of proteolytic enzyme activity measurements in larval fish research, as well as its use in aquaculture nutrition research, was confirmed. Protein content, increase in length and survival rates of the sea bass larvae were additionally determined in order to evaluate an influence on the diet. The protein content of larvae fed the Artemia nauplii was higher and the growth of larvae fed the compound diet was reduced. Larval mortality was not affected by the diet given.