Is Hemoglobin Gelation an Adaptation to the Cold in Boreal Fishes?

Recent studies of fish red blood cells found that a regular paracrystalline array of hemoglobin (Hb) tetamers formed under low oxygen conditions in 2 species of boreal fishes, Atlantic cod (Gadus morhua) and toadfish, (Opsanus tau). This phenomenon is termed hemoglobin gelation and its physiological characteristics and importance to survival of boreal fishes is unknown. The study outlined in this proposal will obtain preliminary data on the frequency and physiological nature of the phenomenon of hemoglobin (Hb) gelation in red blood cells of fishes that inhabit cold-water temperate and Arctic environments. The present study will test the hypothesis that hemoglobin gelation within fish red blood cells may be a feature of normal fish respiratory physiology and might be adaptive in extreme cold-water environments. Twelve fish species have been examined to date, and only the cold-water boreal marine fishes exhibited Hb gelation. In one species, Atlantic cod, gelation was relatively mild and did not result in changes in the gross morphology of the blood cells. In a second species, toadfish, gelation resulted in large crystalline structures that disrupted the red cell membranes and ruptured blood cells. The differences in type and severity of Hb gelation among fish species may directly affect their physiology and ultimately play an important part in their capacity for survival. However, too few species have been assayed to determine the extent of hemoglobin gelation in boreal fishes and no data exists on the physiological conditions that facilitate gelation. Few experimental links have been established between gelation and fish hemoglobin structure or between the variation in hemoglobin type and physiology.In this study blood will be sampled from a large number of boreal and Arctic fishes and tested for Hb gelation and the presence of the Hb paracrystalline matrix. These data will provide an accurate assessment of the distribution of the gelation phenomenon within boreal fishes and any correlation with genetic variation within species. Some species of fishes, such as Atlantic cod, have polymorphic hemoglobin in which multiple hemoglobin allotypes are expressed within the red blood cells of the same species. To determine if gelation is associated with hematocrit or with the physiological characteristics of the isoHb components of a species, blood from a representative boreal fish species, Atlantic cod, will be separated into its Hb components and each component will be characterized for oxygen binding functionality and its gelation capacity. The scientific relevance of this is to determine if there are common morphological and physiological traits among hemoglobins of boreal fishes that exhibit gelation and whether these traits are adaptive in extreme environments characteristic of polar regions

The swimming kinematics of larval Atlantic cod, Gadus morhua L., are resilient to elevated seawater pCO2

Kinematics of swimming behavior of larval Atlantic cod, aged 12 and 27 days post-hatch (dph) and cultured under three pCO2 conditions (control-370, medium-1800, and high-4200 μatm) from March to May 2010, were extracted from swim path recordings obtained using silhouette video photography. The swim paths were analyzed for swim duration, distance and speed, stop duration, and horizontal and vertical turn angles to determine whether elevated seawater pCO2—at beyond near-future ocean acidification levels—affects the swimming kinematics of Atlantic cod larvae. There were no significant differences in most of the variables tested: the swimming kinematics of Atlantic cod larvae at 12 and 27 dph were highly resilient to extremely elevated pCO2 levels. Nonetheless, cod larvae cultured at the highest pCO2 concentration displayed vertical turn angles that were more restricted (median turn angle, 15°) than larvae in the control (19°) and medium (19°) treatments at 12 dph (but not at 27 dph). Significant reduction in the stop duration of cod larvae from the high treatment (median stop duration, 0.28 s) was also observed compared to the larvae from the control group (0.32 s) at 27 dph (but not at 12 dph). The functional and ecological significance of these subtle differences are unclear and, therefore, require further investigation in order to determine whether they are ecologically relevant or spurious

Effects of feeding copepod and Artemia on early growth and behaviour of the self-fertilizing fish, Rivulus marmoratus, under laboratory conditions

Growth and survival have often been used as parameters to assess the effects of live feeds on marine finfish, however, behavioural effects, which entail energy cost and may have consequences on fish growth have been given less emphasis. Thus, a 20-day feeding experiment was conducted to determine the effects of copepod Acartia tsuensis (104-732 μm), unenriched, and docosahexaenoic acid, DHA-enriched, first instar Artemia franciscana nauplii (656-906 μm) on growth and behaviour of the mangrove killifish Rivulus marmoratus. Growth was significantly higher in Acartia-fed larvae compared with larvae fed Artemia (unenriched and DHA-enriched) until day 10. On day 20, Acartia-fed larvae had significantly lower growth than fish fed DHA-enriched Artemia. Feeding success was highest in larvae fed Acartia on day 1. Ingestion rate and satiation time did not differ among fish fed different types of feeds until day 20. Swimming activity before feeding was significantly lower in larvae fed Acartia compared with larvae fed Artemia (unenriched and DHA-enriched) until day 10. Higher growth in Acartia-fed fish on day 10 is probably due to the suitable size and high DHA content of A. tsuensis, and lower swimming activity of the larvae. However, on day 20, lower growth observed in Acartia-fed fish may be attributed to the shift in the food size preference of the fish. The present study was able to demonstrate the effects of copepods on growth and behavioural development of marine finfish using R marmoratus as a model animal

Swim-Training Changes the Spatio-Temporal Dynamics of Skeletogenesis in Zebrafish Larvae (Danio rerio)

Fish larvae experience many environmental challenges during development such as variation in water velocity, food availability and predation. The rapid development of structures involved in feeding, respiration and swimming increases the chance of survival. It has been hypothesized that mechanical loading induced by muscle forces plays a role in prioritizing the development of these structures. Mechanical loading by muscle forces has been shown to affect larval and embryonic bone development in vertebrates, but these investigations were limited to the appendicular skeleton. To explore the role of mechanical load during chondrogenesis and osteogenesis of the cranial, axial and appendicular skeleton, we subjected zebrafish larvae to swim-training, which increases physical exercise levels and presumably also mechanical loads, from 5 until 14 days post fertilization. Here we show that an increased swimming activity accelerated growth, chondrogenesis and osteogenesis during larval development in zebrafish. Interestingly, swim-training accelerated both perichondral and intramembranous ossification. Furthermore, swim-training prioritized the formation of cartilage and bone structures in the head and tail region as well as the formation of elements in the anal and dorsal fins. This suggests that an increased swimming activity prioritized the development of structures which play an important role in swimming and thereby increasing the chance of survival in an environment where water velocity increases. Our study is the first to show that already during early zebrafish larval development, skeletal tissue in the cranial, axial and appendicular skeleton is competent to respond to swim-training due to increased water velocities. It demonstrates that changes in water flow conditions can result into significant spatio-temporal changes in skeletogenesis

Feeding behaviour and digestion physiology in larval fish – current knowledge and gaps and bottlenecks in research

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

Review of the projected impacts of climate change on coastal fishes in southern Africa

The coastal zone represents one of the most economically and ecologically important ecosystems on the planet, none more so than in southern Africa. This manuscript examines the potential impacts of climate change on the coastal fishes in southern Africa and provides some of the first information for the Southern Hemisphere, outside of Australasia. It begins by describing the coastal zone in terms of its physical characteristics, climate, fish biodiversity and fisheries. The region is divided into seven biogeographical zones based on previous descriptions and interpretations by the authors. A global review of the impacts of climate change on coastal zones is then applied to make qualitative predictions on the likely impacts of climate change on migratory, resident, estuarine-dependent and catadromous fishes in each of these biogeographical zones. In many respects the southern African region represents a microcosm of climate change variability and of coastal habitats. Based on the broad range of climate change impacts and life history styles of coastal fishes, the predicted impacts on fishes will be diverse. If anything, this review reveals our lack of fundamental knowledge in this field, in particular in southern Africa. Several research priorities, including the need for process-based fundamental research programs are highlighted