The potential of the unicellular green algae Chlorella vulgaris and Scenedesmus obliquus and the filamentous green algae Cladophora glomerata and Hydrodictyon reticulatum as protein sources in Oreochromis niloticus and Tilapia zillii diets was investigated. When O. niloticus and T. zillii were fed with fresh C. vulgaris and S. obliquus, a high percentage of the ingested algae was found to be undigested. Heat treatment of the algae at 40°, 60°, 80° and 100°C produced increased growth and protein utilizations in the fishes compared to those fed the untreated algae. Feeding C. vulgaris treated at 100°C for 30 minutes and S. obliquus treated at 100°C for 15 minutes was found to have produced the best growth responses in O. niloticus and T. zillii. C. glomerata meal and H. reticulatum meal were each fed separately as fishmeal substitutes in pelleted rations formulated to contain 30% protein with varying proportions of this supplied by the fishmeal and the algal meal. A diet containing 25% protein supplied by the algal meal alone was also fed. When 5% of the fishmeal protein was replaced with algal protein (both C. glomerata and H. reticulatum) and fed to T. zillii, the growth and protein utilization values recorded were superior to those obtained for the control 30% fishmeal protein diet. Higher levels of algal protein substitution were, however, found to produce poorer growth and protein utilization values in both fish species. Diets containing only algal protein (both C. glomerata and H. reticulatum) produced the poorest growth responses in both fish species. Hydrodictyon reticulatum was found to be limiting in methionine and histidine. Supplementation of these essential amino acids produced improved growth in both O. niloticus and T. zillii. It was concluded from these studies that the green algae evaluated may be suitable partial dietary protein sources for tilapias.

A study has been carried out to investigate some aspects of the feeding and digestion of the parasitic copepod Lepeophtheirus salmonis (Kreyer, 1837), a serious pathogen of wild and farmed marine salmonids. The alimentary canal consists of a cuticularised foregut and hindgut and a midgut, the latter comprising most of the length of the alimentary canal. It consisted of an anterior diverticulum, and anterior midgut, mid midgut and posterior midgut. All the midgut is lined in the luminal side with a monolayer of digestive epithelium. The latter is supported by a porous basal membrane. Mesenteries suspend the gut in the haemocoel and attach to the basal membrane by means of extensions of their cytoplasm that interlock with the pores of the basal membrane and are intimately associated with the cellular basal membrane of the enterocytes. Four types of cells could be recognised ultrastructurally and were named according a widely accepted nomenclature for the types of digestive epithelial cells found in decapod crustaceans. R-cells were the most abundant type and were believed to be involved in the absorption of nutrients, storage of lipids and probably excretion of waste material. Once the R-cells have finished their useful life, it is proposed that they finally die after passing through a stage, called A-cell stage, comparable to apoptosis or programmed cell death, after which the A-cell is finally sloughed off the epithelium and discarded in the faeces. F-cells constituted the second cell type, in charge probably of the secretion of digestive enzymes. Once this stage is finished, F-cells are believed to transform into the third type of cells, the B-cells, which engage in intracellular digestion of nutrients. At the end of their useful life they are sloughed off the epithelium. The last cell type, the E-cells, are believed to be embryonic cells that differentiate either into R- or F-cells. A revised mode of feeding is proposed, in which the louse scoops up strips of host skin epithelium of relatively constant size and shape, by means of the structures associated with the mouth cone. Analysis of the gut contents and the faecal pellets revealed that the main food item was host skin epithelium. The feeding activity usually reaches the dermal layer, suggested by the common occurrence of host melanin in the gut and in the faecal pellets. Two types of faecal pellets were found. The first type was a cylindrical one which was made of the ingested host's epithelial cells with little signs of having being digested. Cylindrical pellets could be clear or dark depending on the amount of host melanin present in them. The second type of pellet was a tape- or ribbon-like gelatinous pellet produced mainly when the lice were not eating (as during starvation) or sometimes associated to the end of the cylindrical pellets. Pellets were always surrounded by a delicate peritrophic envelope composed of several peritrophic membranes. Blood was believed to be another important food item. Blood feeding was commonly associated with the production of lipids in the R-cells and it is proposed (but not confirmed) that this alternative food item could be associated with some physiological process that requires lipogenesis, like vitellogenesis. A method for manually feeding the lice was devised. Salmon blood and milk were fed in this way. No sign of digestion of these food items was observed suggesting that possibly an endogenous factor different from the presence of food in the gut is necessary to trigger the digestive process. An analysis of type of gut contents, peritrophic membranes and cell type occurrences during a digestive period was carried out. The results suggested that some digestive processes take place preferentially in one or another gut region. Mid and posterior midgut are probably associated with the production of faecal pellets, production of digestive enzymes, intracellular digestion and excretion of waste materials judging by the higher occurrence of peritrophic membranes, B- and A-cells in these regions. Absorption of nutrients probably takes place throughout the midgut. The morphological changes in the topography shown by the midgut epithelium suggest that it is a very active and plastic tissue. The results of this study were discussed and compared with similar studies of other crustaceans, including other parasitic and free living copepod species. Suggestions were made of the implications of the present findings in the search for a control method for this parasite.

Many studies have been conducted on the effect of size-grading in other fish species. However, there is a paucity of scientific information on the effects of size variation on cannibalism of juvenile dusky kob. Thus, a study focusing on the effect of size variation on juvenile dusky kob aggressive and feeding (browsing) behaviours was conducted. Three separate groups of hatchery-reared juvenile dusky kob of were obtained from Oceanwise (Pty) Ltd for use in a series of three experimental trials. In all trials, juvenile fish of the same age were size-graded and the COV-value was used to determine the size variation. The focal fish (largest fish) was exposed to groups of fish with different size variation for 30-min. behavioural observations before and after feeding in randomised trials. The first experimental trial (Chapter 2) quantified the effect of increasing size variation and observation time on the aggressive and browsing behaviours of juvenile dusky kob. On average, juvenile dusky kob weighed 3.60 ± 0.68 g fish-1 and measured 5.8 ± 0.41 mm. Each focal fish was observed (a) before feeding in the morning, (b) 2 h after feeding, (c) 6 h after feeding and (d) 12 h after feeding. Fish increased browsing behaviours (averaging 6.60 ± 0.56) and decreased intimidating aggressive behaviours (18.60 ± 1.39) 12 h after feeding. Other aggressive behaviours occurred but did not differ between observation times. Aggressive and browsing behaviours positively correlated with size variation variables, predominantly, 12 h after feeding. An average frequency of 19 chases were observed positively correlated with size variation, followed by average frequencies of 17 body bites and browses, and 11 tail bites per 30 min. Some behaviours including average frequencies of 0.2 chases, 4 tail bites, 2.4 intimidating and 0.3 browsing behaviours negatively correlated with the size variation, generally closer to the last meal. These preliminary observations thus showed that fish have become hungry approximately 6-12 h after feeding and substituted certain behaviours for others as time after feeding passed and as size variation increased. The second experimental trial (Chapter 3) consisted of the observations further testing the relationship between aggressive behaviours and size variation of juveniles of dusky kob averaging 0.43 ± 0.27 g fish-1. The focal fish was exposed to groups of fish of four size variation (COV) treatments for observations before and 12 h after feeding. Aggressive behaviours positively correlated with size variation both before and 12 h after feeding. An average frequency of 437 body bites positively correlated more often with COV, followed by average frequencies of 365 intimidating behaviours and 199 tail bites per 30 min., respectively, before and 12 h after feeding. The least often exhibited aggressive behaviours averaged 26 chases while positively correlating with size variation on the times specified. An average frequency of 311 intimidating behaviours before and after feeding including average of 28 tail bites after feeding negatively correlated with size variation. This may relate to shift of behaviours depending on the needs and capacity of the fish. Apparently, aggressive fish can change its behaviour as a function of COV-values rather than the mean size of the other fish. The third trial (Chapter 4) investigated the effect of the aggressor’s (focal fish) size in relation its aggressive and browsing behaviours to other fish (non-focal fish). Juvenile fish used for this trial, on average, weighed 30 ± 7.63 g fish-1. Aggressive and browsing behaviours were observed in four treatments of a) high COV and mean weight below, b) low COV and mean weight less, c) high COV and mean weight equivalent to and d) low COV and mean weight higher than that of the focal fish. Increased frequencies of aggressive and browsing behaviours per 30 min. occurred in treatment A, sharing similar frequencies in treatment C, compared to the other treatments (B and D) which shared certain frequencies. The intimidating behaviours predominated, followed by browsing, body bites, chases and tail bites, respectively. The results of the overall study suggest that the time passed after feeding and increasing size variation and differences facilitated aggressive and browsing behaviours in juvenile dusky kob. Dusky kob showed increasing aggressive behaviours as early as in the first two weeks after hatching, averaging 0.43 ± 0.27 g fish-1 with the frequency correlating with size differences. Consistent size-grading technique in the same-age fish should be used to manage size variation associated with aggressive behaviours. The period of about 4-6 h after feeding may explain the noticeable increased aggressive and browsing behaviours. Thus, fish should be fed immediately before or after evacuation of their guts to maintain less-aggressive behaviours of juvenile dusky kob. Fish generally increased aggressive and browsing acts before and long time after feeding than closer to after feeding. The study has provided the fundamental scientific groundwork for fish farmers and future researchers can further explore size variation, time after feeding and gut evacuation rate as critical components of aggressive behaviours. The scientific knowledge of aggressive and cannibalistic behaviours has essential application in farming management to achieve improved survival and growth rates in juvenile fish.

The three components of the aerobic respiratory metabolism of sablefish, digestion (SDA), activity, and standard metabolism, were examined separately and together as dependent variables responding to the independent variable, feeding frequency. All fish were similar in size and held within a temperature range of 8.5 - 9.5 C on a 12 hr photoperiod. Fish were studied in both 4000 L mass respirometers equipped with activity meters and in a tunnel respirometer. Identical meals were given every 4, 7, and 14 days. A fourth series of starved fish served as controls. In the mass respirometers, oxygen consumption, ammonia nitrogen excretion, and activity were monitored continuously before, during, and after acclimation to the different feeding frequencies. This permitted estimation of total metabolism, the activity and feeding components of total metabolism, standard metabolism, and protein and lipid catabolism. In the tunnel respirometer, energy expenditures at similar levels of Imposed activity were compared before and after eating to examine repartitioning of locomotor and feeding metabolism. It was found that swimming energy expenditures and standard metabolism are a sigmoid functions of ration frequency. The lowest metabolic rates are associated with the least frequent feedings and the greatest with the most frequent meals. Consequently, total and routine metabolic rates are also direct functions of ration history. The lowest metabolic rates are based on lipid oxidation as an energy source. The fish primarily oxidize proteins to meet metabolic needs when on higher rations. It is also shown that apparent specific dynamic action (SDA) results to a greater extent from catabolic rather than anabolic processes. When the dual metabolic load of locomotion and digestion threatens to exceed the aerobic metabolic scope of the fish, a physiological mechanism exists whereby oxygen supply is preferentially shunted to locomotor requirements. When spontaneously active in the mass respirometers, the activity component of metabolism is generally less than 25% of the standard metabolic rate and digestion and locomotion can proceed synchronously. When swimming spontaneously, the sablefish move at a single, probably optimal velocity regardless of ration history. The better fed fish in the experiments were active most of the day despite the low contribution of the activity component to the routine metabolic rate. These results have significance regarding assumptions often made in bioenergetic models, specifically that activity energy expenditures and standard metabolic rates are independent of ration. They reveal an adaptable physiology which applies different energy partitioning strategies to meet the changing metabolic needs of fish in a dynamic environment with a variable food supply. / Science, Faculty of / Zoology, Department of / Graduate

Laboratory feeding experiments showed that sympatric Dolly Varden charr (Salvelinus malma) were able to locate and consume prey targets at lower irradiance levels than sympatric cutthroat trout (Salmo clarki clarki) but their acuity was poorer. Reaction distance (RD) of both species to artificial and natural prey targets increased as irradiance level increased from a visual irradiance threshold (VIT), an irradiance level below which prey targets were not detected visually (3.0 x 10¹⁴ photons m⁻²s⁻¹ for charr and 3.0 x 10¹⁵ photons m⁻² s⁻¹ for trout) to a saturation irradiance level (SIL) which produced the maximum RD (3.0 x 10¹⁶ photons m⁻² s⁻¹ for charr and 6.6 x 10¹⁸ photons m⁻² s⁻¹ for trout). The VIT and SIL were independent of prey type and prey characteristics in both species. At all irradiance levels greater than the VIT of trout, the RD of trout exceeded that of charr for the same prey type. At a given irradiance level the largest RD in both species occurred in the presence of red irradiance followed in decreasing order by green, yellow and blue irradiance. Reaction distance of trout and charr increased with increases in prey size, movement and contrast. The percent increase in RD was greatest in trout. Between the VIT and the SIL the percent increase in RD was greater at higher irradiance levels in both species. At or above the SIL the percent increase in RD was constant. The central portion of retinas of trout and charr from sympatric and allopatric populations were examined by light microscopy. The two trout populations had a similar density of cone cells and higher than either charr population. Sympatric charr had the lowest cone cell density and allopatric charr intermediate density. Rod cell density showed the opposite trend, being highest in sympatric charr, lowest in sympatric and allopatric trout and intermediate in allopatric charr. The cone cell mosaic, consisting of a regular array of double and single cones, was the same in all four populations. Both cone types were smallest in the two trout populations, largest in the sympatric charr population and intermediate in allopatric charr. The degree of retinal summation was greatest in sympatric charr, least in the trout populations and intermediate in allopatric charr. In summary, histological studies indicated that sympatric and allopatric trout possessed the highest level of visual acuity while sympatric charr were the most sensitive to low irradiance conditions. Foraging velocity of sympatric trout and charr increased as irradiance increased reaching a maximum at the SIL of each species. From foraging velocity, RD and information on the diel irradiance regime in Loon Lake I estimated the volume of water searched visually for two natural prey types by trout and charr on a mid-summer day. Below the VIT, only charr were able to locate and consume buried prey targets, presumably by employing their chemosensory system. Differences in visual and non-visual feeding behaviour in sympatric trout and charr and in retinal structures of sympatric and allopatric trout and charr are generally as expected based on field studies of their vertical distribution and feeding habits. / Science, Faculty of / Zoology, Department of / Graduate

Sympatric populations of Dolly Varden (Salvelinus malma) and cutthroat (Salmo clarki clarki) are spatially and food segregated in Loon Lake, British Columbia. Dolly Varden are found mainly in the lower water column, while cutthroat are found in the middle and upper water column. Zooplankton, the only major prey type found in both diets, appear more important to the cutthroat. The purpose of this study was to determine whether this segregation was due to behavioural interactive processes or genetically based selective processes. This was investigated by the segregation and transferral of the members of the two populations to separate fishless lakes. In addition, field studies examined selective feeding on zooplankton and laboratory studies compared the feeding behaviour and abilities of Dolly Varden and cutthroat on three different types of zooplankton. Little change occurred during the two year sampling period in either the diet or the vertical distribution of the two species, an indication that the fish were not interactively segregated. However, the physical and biological characteristics of the lakes may have reinforced, at least initially, previous behaviour patterns. As a result, more time may be required to properly assess the final results. Laboratory results indicate that primarily Chaoborous larvae and secondarily Daphnia pulex were the preferred prey types to both fish predators, mainly because of their poor escape response when compared to that of Diaptomus kenai. The abundance of these prey types in the diet of lake-caught fish was generally in accordance with the laboratory preferences. These results also demonstrated that cutthroat were more efficient planktivores than were Dolly Varden. / Science, Faculty of / Zoology, Department of / Graduate

The Bat Ray, Myliobatis californica Gill, occurs from Oregon to the Gulf of California and is common in California bays during the spring and summer. MacGinitie (1935) observed that during its feeding activities, the Bat Ray can dig channels up to 1 meter wide, 50 cm deep and 4.5 meters long in benthic substrates. In intertidal sand flats in Tomales Bay, California, circular pits up to 1 meter in diameter and 20 cm in depth are made by Bat Rays in late summer. In some areas over 50% of the sand flat surface is covered with Bat Ray pits. This recurrent seasonal disturbance of the substrate due to Bat Ray predation on benthic communities may be important in affecting their structure and faunistic composition. In preliminary studies of the effects of predation on benthic communities in Tomales Bay, we were interested in obtaining information about changes in diets of Bat Rays in relation to size.

Aquaculture production is increasing annualy and wild fisheries for fishmeal production remain stagnant. As a consequence, extensive research has been deployed to reduce dietary fishmeal inclusion in feeds of farmed species. Usage of alternative protein sources derived from plants continues to increase with the most popular sources being oilseeds, legumes and cereal grains. The downside of these sources is that most of them could directly be used for human consumption arising legitimate criticism from voices referring to countries where protein shortages lead to malnutrition among the population. Jatropha curcas is a tropical oilseed with upcoming popularity for sustainable fuel sourcing. The plant is thought to thrive in semi-arid and arid areas, not just producing oil, but at the same time reclaiming previously eroded land for the local population. For these reasons, annual cultivation of Jatropha curcas is thought to rise over the next decades. After oil is extracted from the seed, the remaining press cake, is currently used as a fertilizer or energy source. This is mostly due to toxic phorbol esters that until recent- ly limited any nutritional applications. In 2011, a method to detoxify Jatropha press cake was developed and paved the way for nutritional research on the resulting detoxified Jatropha curcas kernel meal (JKM) to be launched. JKM offers very high protein content with a balanced amino acid composition suggesting opportunities for usage as a feedstuff in aquaculture diets. JKM further has higher mineral content than comparable oilseeds. However, potential anti-nutritional factors (ANFs) present in the meal could lead to impairment of nutrient availability or other adverse effects. Previous research has already started to evaluate JKM as a protein source for a variety of aquaculture species. This thesis attempts to further identify the potential of JKM as a protein source and assess the effects of JKM on the development of two model cultured teleost species, common carp (Cyprinus carpio) and Nile tilapia (Oreochromis niloticus), as they represent two of the most farmed species, particularly in the tropics. The work comprises growth trials on both species using fishmeal as a subject of replacement in solely fishmeal protein-based diets and on more practical fishmeal/plant protein-based diets. It engages with the effects of phytate, a prominent component of JKM with potential anti-nutritional attributes and commercially available phytase feed supplements to diminish these attributes, as well as oxalate, another plant-specific component with high concentrations in JKM and with limited attention in aquaculture nutrition research. Carp and tilapia showed varying results with different inclusion levels of JKM. For carp 50% fishmeal replacement was possible without losses in growth in diets where fishmeal was the only bulk protein source (Chapter 3.1), Tilapia showed slightly worse growth at a 30% replacement level (Chapter 3.2). A steep decline in growth could be observed when replacing 100% fishmeal with JKM in carp (Chapter 3.1), while tilapia showed no difference at that level compared to 30% replacement (Chapter 3.2). In practical diets, 100% of fishmeal could be replaced by JKM without any adverse effects on growth of carp (Chapter 3.3), while tilapia showed a slight, but significant linear negative correlation with higher inclusion levels of JKM (Chapter 3.4). Phytase addition in tilapia feeds was identified as having no obvious impact on growth in JKM based diets where enough available phosphorus was provided through mineral supplementation (Chapter 4.1). In JKM based diets where available phosphate was not added, phytase addition showed a tendency to increase growth and significantly increased mineral retention and decreased phosphorus effluent contamination (Chapter 4.2). Phytase application through pre-incubating JKM along with citric acid exerted a positive effect of growth on carp when fishmeal protein was replaced by 50% (Chapter 3.1). Phytase was further shown to completely hydrolyze phytate in vitro; however, incomplete hydrolysis was observed in vivo in tilapia (Chapter 4.3). Dietary soluble oxalate added to fishmeal based diets for carp showed better growth parameters, nutrient and mineral retention at inclusion levels 1.5% and higher (Chapter 5.1). For tilapia, a trial could demonstrate adverse effects of oxalate on potassium, calcium, manganese and zinc digestibilities, in this case without negative effects on growth (Chapter 5.2). For both, carp and tilapia, an impact of oxalate on lipid metabolism was evident, lowering body lipid content and blood cholesterol in inclusion levels from 1.5% or higher. JKM can become a valuable alternative to present dietary protein sources in aquaculture feeds. The nutritional attributes of JKM need further research, especially longer-term testing in a commercial scenario and application in commercially produced feeds. Results of this thesis pose a useful addition to previous research and can be referred to for realizing these next steps.

No description available.

Distribution, diet, and food availability for young-of-the-year (YOY) largemouth bass (Micropeterus salmoides), YOY bluegill (lepomis macrochirus) and threadfin shad (Dorosoma petenense) were studied to reveal any potential interactions in Patagonia Lake, a 170 ha (265 acre) recreational impoundment in Santa Cruz County, Arizona. Threadfin shad, a forage species, were stocked to enhance the growth of bass. As shad became abundant, limnetic zooplankton declined, reducing the primary food supply of the YOY game fish. Diet analysis showed very little food overlap between YOY gamefish and threadfin shad. Shad ate phytoplankton when zooplankton became scarce, and continued to grow well and reproduce. As zooplankton decreased, YOY gamefish shifted their diets to aquatic insects. After the shift, the gamefish did not grow well. The continuous overgrazing of zooplankton by large numbers of threadfin shad had an impact on the growth of the juvenile largemouth bass and bluegills. This impact may result in weak year classes in the future.