Optimal dietary carbohydrate‐to‐lipid ratios for silvery‐black porgy (Sparidentex hasta) juveniles

Four isonitrogenous diets containing different carbohydrate:lipid (CHO:L) ratios (0.3, 0.6, 1.1 and 1.8) were tested in triplicate groups (16 fish per replicate) of silvery‐black porgy juveniles for 8 weeks. Growth performance was not affected by different dietary CHO:L ratios (P > 0.05); however, the viscerosomatic index, the intraperitoneal fat, whole‐body lipid, energy and n‐3 long chain polyunsaturated fatty acids levels increased with decreasing dietary CHO:L ratios (P < 0.05). Fish fed with 1.8 CHO:L diet had the lowest apparent digestibility coefficients of protein and lipid, as well as the lowest plasma haemolytic and lysozyme activities (P < 0.05). Red blood cell counts and plasma glucose levels were higher in fish fed with 1.1 and 1.8 CHO:L ratio diets than in the other groups (P < 0.05). Plasma alkaline phosphatase and alanine aminotransferase, as well as the level of lipid peroxidation and total antioxidant capacity in the liver and plasma increased as dietary CHO:L ratios decreased (P < 0.05). The results of the current study indicated that the diets with CHO:L ratios between 0.6 and 1.1 are optimal for silvery‐black porgy, whereas higher ratios may result in hyperglycaemia and immune suppression, and lower CHO:L ratios may lead to oxidative stress and liver dysfunction.     

Choline supplementation increased total body lipid gain,while surplus methionine improved growth and amino acid retention in adult Atlantic salmon (Salmo salar)

Methionine–choline‐deficient (MCD) mammals are known to accumulate liver TAG probably due to phosphatidylcholine (PC) deficiency and thus assembly of VLDL and transport of lipids from liver to peripheral organs. To assess whether supplementation of choline could spare methionine and secure a healthy liver metabolism, by reducing the endogenous PC synthesis without interfering with lipid transport and distribution, Atlantic salmon with initial BW of 700 g were fed adequate (1.9 g Met/16 gN) or surplus methionine (2.5 g Met/16 gN) diets of which were supplemented with choline or not for a period of 19 weeks. Fish fed the low‐methionine diets had reduced growth (p = .013) due to reduced protein gain (p = .007), while lipid gain slightly improved in fish fed the choline‐supplemented diets (p = .047). Also, feed conversion improved when fed surplus methionine (p < .001), while choline supplementation had no impact on feed conversion. No interaction between choline and methionine on growth performance or retention existed. Phospholipid status in liver and muscle was not affected by treatments, and no liver TAG accumulation occurred at the methionine levels used. Gene expression of ApoB100 necessary for assembling VLDL or pemt necessary for endogenous PC synthesis was unaffected by treatments. Capacity of methylation (MAT, BHMT) within the liver was not affected by treatment nor was the gene expression of enzymes in liver transsulfuration (CBS or CDO). Methionine status within liver was unaffected by treatments, while free methionine reduced in those fish fed the low‐methionine diets in muscle and plasma. Cystathionine and taurine were elevated when fed surplus methionine. Choline supplementation had no impact on sulphur amino acid metabolites in either tissue. Neither did choline supplementation improve TAG mobilization from liver to muscle. To conclude, choline does not improve endogenous phospholipid synthesis or transport of TAG from liver to muscle depot when added to diets containing 1.9 g Met/16 gN, while surplus methionine improved growth and protein retention, indicating that 1.9 g Met/16 gN is enough to support a healthy liver metabolism, but too low to support muscle protein deposition in adult salmon fed high plant protein diets for longer periods of time.     

Isolation of infectious microalga Prototheca wickerhamii from a carp (Cyprinus carpio) – a first confirmed case report of protothecosis in a fish

Protothecosis is a rare infection caused by environmentally ubiquitous achlorophyllic microalgae of the genus Prototheca. Here, we describe a first case of protothecosis in a carp (Cyprinus carpio), which is at the same time the first case of protothecosis in a fish, confirmed by phenotype‐ and molecular‐based methods, including PCR sequencing of the rDNA cluster and protein profiling using matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry.     

Immunostimulatory effects of dietary poly‐β‐hydroxybutyrate in European sea bass postlarvae

The stable production of high‐quality fry in marine aquaculture is still hampered by unpredictable mortality caused by infectious diseases during larval rearing. Consequently, the development of new biocontrol agents is crucial for a viable aquaculture industry. The bacterial energy storage compound poly‐β‐hydroxybutyrate (PHB) has been shown to exhibit beneficial properties on aquatic organisms such as enhanced survival, growth, disease resistance and a controlling effect on the gastrointestinal microbiota. However, the effect of PHB on the developing immune system of fish larvae has so far not been investigated. In this study, the effect of feeding PHB‐enriched Artemia nauplii on survival, growth and immune response in European sea bass (Dicentrarchus labrax) postlarvae was examined. Amorphous PHB was administered to 28‐day‐old sea bass postlarvae over a period of 10 days. The survival and growth performance were monitored, and the expression of 29 genes involved in immunity, growth, metabolism and stress‐response was measured. While the expression of the insulin‐like growth factor 1 (igf1), an indicator of relative growth, was upregulated in response to feeding PHB, the larval survival and growth performance remained unaffected. After 10 days of PHB treatment, the expression of the antimicrobial peptides dicentracin (dic) and hepcidin (hep) as well as mhc class IIa and mhc class IIb was elevated in the PHB fed postlarvae. This indicates that PHB is capable of stimulating the immune system of fish early life stages, which may be the cause of the increased resistance to diseases and robustness observed in previous studies.     

What the past tells us about the future of Pacific salmon research

The Larkin lectures are held every two years at the University of British Columbia in recognition of Dr. Peter Larkin's contributions to fisheries science. The lecture I presented in November 2015 coincided with an announcement that the Institute of Fisheries that Peter Larkin founded in the 1960s would be restructured as the “Institute for Oceans and Fisheries” with an emphasis on fisheries and oceans issues important to British Columbia as well as the rest of the world. I decided to look back at research issues that Peter Larkin thought would be important for Pacific salmon (Oncorhynchus spp.) in the future and see what has happened as a way of identifying the complexity that the Institute for Oceans and Fisheries in particular and the science community in general will face. I chose five themes from Peter Larkin's talks: 1 understanding marine survival, 2 ocean carrying capacity, 3 aquaculture, 4 climate, Pacific salmon and climate change and 5 informing the public, and then added my opinion about research priorities for the future. Peter Larkin recognized the future relevance of these examples, but he probably could not have imagined how these and related issues will challenge his renamed institute and the rest of the research community over the next 50 years.     

Understanding farmers’ potato production practices and use of improved varieties in Chencha,Ethiopia

This study was carried out to better understand non-adoption of improved varieties of potato (Solanum tuberosum) and associated technologies by smallholder farmers in Chencha, Ethiopia. Data were collected through a survey (n = 47) and in-depth interviews (n = 20). It shows how wealth status was a factor of major importance. Most wealthy and some medium-wealthy farmers adopted improved potato varieties and many of the improved production practices; they had access to seed, associated knowledge and support, and sufficient resources that were necessary to apply the improved practices. Non-adoption was common among many medium-wealthy and most poor farmers: they lacked—next to access to the technologies and knowledge—cash, land, and labor. Results indicated the need to rethink research and intervention efforts. Next to paying attention to differences in the access to technology and the related knowledge, there is a need to consider the variation in technology needs, supporting microcredit services, and room to experiment. As a result, different combinations of improved production practices may be adopted.     

Apparent digestibility coefficients of animal and plant feed ingredients for juvenile Pseudobagrus ussuriensis

A study was conducted to determine apparent digestibility coefficients (ADCs) of dry matter (DM), crude protein (CP), lipid, gross energy, phosphorus and amino acids (AAs) from Peruvian fish meal (PFM), native fish meal (NFM), meat bone meal (MBM), dried daphnia meal (DDM), soybean meal (SBM), full‐fat soybean (FSBM), cottonseed meals (CSM), rapeseed meal (RSM) and corn gluten meal (CGM) for Pseudobagrus ussuriensis (7.8 ± 0.06 g). Test diets were formulated to contain a 70:30 mixture of reference diet to test ingredient with chromic oxide (5 g kg^–1) serving as the inert marker. ADCs of DM ranged from 49.94% (CGM) to 87.11% (PFM), the highest ADCs of DM were observed in PFM and the lowest was found in CGM. ADCs of CP in the test ingredients ranged from 74.92% (CGM) to 93.41% (SBM). ADCs of crude lipid ranged from 51.80% (CGM) to 94.07% (PFM) for fish. ADCs of energy ranged from 56.42% (CGM) to 90.09% (PFM). ADCs of phosphorus ranged from 21.81% (CSM) to 65.70% (PFM). AA availability for the test ingredients followed a similar pattern to ADCs of CP, in which values for PFM, NFM and MBM were generally higher (p < .05) than those of other protein ingredients. Among all plant meals, the AA availability values in SBM were higher (p < .05) than those in CGM, CSM and RSM. The availability of most AAs in CGM was the lowest (p < .05) among all tested ingredients. In conclusion, PFM and NFM are good sources of available protein and AAs. When fishmeal supply is limited, MBM and DDM are substitutes for fishmeal reduction in P. ussuriensis diets; at the same time, SBM and FSBM are also very acceptable protein feedstuffs. However, CSM, RSM and CGM could not be used at high levels in P. ussuriensis diets because of their inferior digestibilities.     

Cyprinid herpesvirus 3 as a potential biological control agent for carp (Cyprinus carpio) in Australia: susceptibility of non‐target species

Carp (Cyprinus carpio L.) is a pest species in Australian waterways, and cyprinid herpesvirus 3 (CyHV‐3) is being considered as a potential biological control (biocontrol) agent. An important consideration for any such agent is its target specificity. In this study, the susceptibility to CyHV‐3 of a range of non‐target species (NTS) was tested. The NTS were as follows: 13 native Australian, and one introduced, fish species; a lamprey species; a crustacean; two native amphibian species (tadpole and mature stages); two native reptilian species; chickens; and laboratory mice. Animals were exposed to 100–1000 times the approximate minimum amount of CyHV‐3 required to cause disease in carp by intraperitoneal and/or bath challenge, and then examined clinically each day over the course of 28 days post‐challenge. There were no clinical signs, mortalities or histological evidence consistent with a viral infection in a wide taxonomic range of NTS. Furthermore, there was no molecular evidence of infection with CyHV‐3, and, in particular, all RT‐PCRs for viral mRNA were negative. As a consequence, the results encourage further investigation of CyHV‐3 as a potential biocontrol agent that is specific for carp.     

Fluorescence of Extracts from Argentine Hake (Merluccius hubbsi) Muscle and Its Correlation with Quality Indices During Chilled Storage

Argentine hake (Merluccius hubbsi) was stored chilled for 8 days. The evolution of fluorescence of the aqueous and organic extracts of muscle during storage at 4°C was studied and correlated with common damage indices; pH, total volatile basic nitrogen, free fatty acids, and the fluorescence intensity of the aqueous phase showed a good correlation with storage time. The excitation-emission matrices of the aqueous extracts were also obtained. A fluorescence landscape that could be attributed to tryptophan decreased with storage time, meanwhile a peak (around 340 and 400 nm for excitation and emission wavelengths, respectively) is developed during chilled storage.     

Interactions of baseflow habitat constraints: Macroinvertebrate drift,stream temperature,and physical habitat for anadromous salmon in the Calapooia River,Oregon

1. The Calapooia River in western Oregon supports a small winter steelhead trout (Oncorhynchus mykiss) population and historically supported spring Chinook salmon (Oncorhynchus tshawytscha). Early timber harvesting removed the riparian forest, and log transportation practices simplified the channel. Those disturbance legacies continue to affect fish habitat by limiting shade and channel complexity, complicating conservation efforts.
2. To evaluate juvenile salmonid rearing potential, macroinvertebrate drift, thermal regime and physical habitat were measured at eight sites in 24 km of the upper river during late summer baseflow.
3. Overall physical habitat was simple, with few functioning instream structures or pools. During the 22‐day drift study, flows declined and maximum site stream temperatures ranged from 23.1°C at the lower end to 16.4°C 24 km upstream.
4. Macroinvertebrate drift concentrations ranged from 0.7–13.7 ind. m^?3 with biomasses from 0.02–1.23 mg m^?3. Drift concentration biomass was higher upstream (P  = 0.006) than downstream and declined overall (P  < 0.001) during the study. Drift biomass was dominated by five taxon groups – Baetis tricaudatus, Calineuria californica, Hesperoperla pacifica, Simulium spp., and Chironomidae, which were 65% of total biomass. During twilight, total biomass and biomass of B. tricaudatus, Simulium spp., and Chironomidae (both larvae and adults) were higher.
5. Total drift declined dramatically over the study period owing to decreases in drift concentration and a 58% decline in discharge, greatly reducing overall drift and available food resources for juvenile‐rearing salmonids.
6. The upper catchment, both with cooler temperatures and higher food availability, provided the best conditions for juvenile anadromous salmonids to survive late summer conditions. Conservation consequences of climate change‐induced alterations in flow and temperature may further affect habitat quality for juvenile salmonids in this catchment in the coming decades.